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Copyright © 1971, 2009, By Refrigeration Service Engineers Society. -1-

Service Application ManualSAM Chapter 630-31

Section 12

RESIDENTIAL AND LIGHT COMMERCIAL GAS-FIRED HEATING EQUIPMENTBy: Jack Linville

INTRODUCTION

Objectives –This section is intended to provide the Installation and Service Engineer with the background information necessary to supplement the working knowledge he gains on the job as a means to provide his clients with fast, efficiently-installed and well-maintained heating systems and at the same time create confidence on the customers part that this is what he is getting. To further overwork an often misused slogan, “we must service what we sell.” But it does not end here, we must also sell what we service. It is very important that the customer is made to understand before and after the fact just what was involved, why it was necessary for you to perform certain services and what he can reasonably expect in the future for his equipment.

SCOPE

The scope of this section will be confined to the most commonly used automatically controlled vented gas fired heating equipment for residential and light commercial use. This discussion will be limited to units fired at 400,000 or less Btu per unit or per section, as firing rates above this point get us into the complex electronic control and double safeguard systems required by fire insurance associations such as FIA and FM or anything covered by their member companies. We will also assume at this point that all equipment discussed bears the American Gas Association seal indicating that the design has been tested and certification issued in writing to the manufacturer indicating that requirements as adopted by the American National Standards Institute have been met. This seal indicates that the design tested meets safety and performance specifications. It is very difficult to compete in the under 400,000 Btu range without this seal or that of another nationally recognized testing agency.

Also excluded are the combination gas heating electric cooling units widely used for rooftop applications. Generally speaking the heating portion of these units functions and is maintained the same as any other forced air heating unit.

At this point it would be well to go over the various types of equipment and define them before proceeding to more specific discussion of their applications.

CONVERSION BURNERS

(Figures 64F45A & 64F45B)

This is a device used as the name implies, for converting existing boilers or warm air furnaces from oil or coal fired to gaseous fuel such as natural and liquefied petroleum (commonly referred to as LP gases) gases. These

Inshot Conversion Burner For Oil to Gas Conversions.

Upshot Conversion Burner For Coal or Oil to Gas Conversions


units may be atmospheric or powered. A power burner receives gas or air or both at pressures, for gas above line pressure and for air, above atmospheric pressure, this extra pressure being applied at the burner.

DUCT FURNACE

These units are designed for installation in a duct system which is equipped with a blower for movement of air. The unit actually becomes a section of the duct work. The unit itself does not contain a blower. See Figure 64F46A for a view of a typical duct furnace.

UNIT HEATER

All components of a unit heater including heat section, automatic gas controls and air moving devices are self contained. By certification definition a unit heater is used for non-residential heating of the space in which it is installed. Certification under unit heater requirements are sometimes obtained for a high-static pressure unit heater for connection to duct work. In this case it is truly a central forced air furnace. (Figure 64F46B)

Duct Furnace. Propeller Type Unit Heater.

Central Gravity Furnace. Horizontal Forced Air Furnace.

Figure 64F46A Figure 64F46B

Figure 64F47AFigure 64F47B


CENTRAL GRAVITY FURNACE

A heating unit which depends on the principle that causes heated air to rise through the duct distribution system and the cooling air to flow back down to the furnace as it cools. NO mechanical air mover is supplied although booster fans are available if needed. (Figure 64F47A)

CENTRAL FORCED AIR FURNACE

This is a heating unit which uses a self-contained blower for air circulation through a duct system. (Figures 64F47B & 64F48)

Floor Furnace.

Vented Wall Heater.

Vented Room Heater.


Central Forced Air Furnace.


VENTED WALL HEATERS

These are self-contained heating units which are mounted from the floor of the space to be heated. Combustion air is taken from outside this space. Note-due to the burn hazard inherent with the hot register, especially to small children, certification under American National Standards will be discontinued. (Figure 64F49A)

VENTED WALL HEATERS

These are self-contained vented appliances complete with grilles or equivalent designed for incorporation in or permanent attachment to the structure of a building, mobile home or travel trailer. Air may be circulated by gravity or fan. (Figure 64F49B)

VENTED ROOM HEATER

A self-contained, vented free-standing appliance for installation in the space to be heated. Not for use with ducts. (Figure 64F50)

APPLICATION

CONVERSION BURNER

This equipment must be designed for the type of conversion to be made. Some burners are designed for mounting in the ash pit of a coal or oil fired boiler or furnace. Others are designed to mount through the firing door of a coal fired furnace or boiler. Some require the use of a job constructed plate to adapt to the opening available. Many of the oil burner replacements are flanged with a bolt circle which fits the existing opening from which the oil burner was removed. Generally speaking a conversion burner for a coal fired furnace or boiler should be of the upshot type which creates the larger flame necessary for good heat transfer in the larger (than oil furnaces) fire boxes. Oil burner replacements are more commonly the inshot type which produces a smaller flame more consistent with the smaller fire box of an oil furnace. See Figures 64F45A & 64F45B for upshot and inshot type burners. In some cases a power burner may be required if the previous fuel required it.

Conversion burners may be used in any type building such as residential, commercial, industrial, public halls, sports areas, etc.

DUCT FURNACES

This equipment is not often used in residential work, being more common on light commercial establishments. As the name implies it goes in a duct which is supplied with circulating air from a separate blower, also located in the duct work. Duct furnaces are seldom the only equipment located in the duct. Most systems using duct heaters will contain in addition to the heating unit a method of cleaning the air such as mechanical or electrostatic filters. Other jobs may incorporate cooling coils served by a remote condensing unit or chiller and equipment for the addition or removal of moisture. The duct furnace is part of a “tailor made” system. We may encounter requirements for heat in a multi zone system with the delivery to the various zones or we may find a need for tempering fresh air up to room temperature where a large amount of air is being exhausted from the occupied space. This is called “make-up air heating.” The units and duct systems may be installed indoor or outdoors depending on how they are designed and certified. Rooftop installations are quite common to conserve usable space in the building. Indoor applications are frequently chosen over a floor mounted system to conserve floor space.

UNIT HEATER

These units provide a very valuable means to decentralize the heating system and put the heat where it is needed as a number of smaller units can be used at various points as required. They are quite often spotted so as to blow heated air along outside walls and are so spaced that a slight overlap of the heated area occurs. It is important that the manufacturers specifications be consulted before selection is made ie: heated areas, throw (distance heated air will travel) and maximum


height above floor which will still allow heated air to strike the floor. There is nothing more uncomfortable than bathing the upper part of the occupant’s body with warm air while the lower limbs are bathed in cold air. Squirrel cage blower type units will generally throw air to the floor from a greater height than the propeller type. These blower types may also be connected to a duct to afford more liberal distribution from a single unit. This duct may be divided into several branches. Return ducts can be used to pull cold air off the floor. It is also possible to filter the air with blower type units. Floor mounted blower units are often used on large industrial jobs where a very long throw of heat is required. Suspended units should be located as low as head room permits.

The suspended, propeller type unit heaters are commonly seen in commercial buildings such as garages, factories, warehouses, show rooms, stores, and for spot heating in isolated spaces such as lobbies, corridors, etc.

CENTRAL GRAVITY FURNACE

These units are becoming less and less popular mainly because they do not permit air filtration and addition of air conditioning and are of little value in one story, ranch style homes. However, in a two story home with a well-designed duct system they can provide the best and most even heat possible with a minimum of maintenance and little or no noise. Initial cost is also relatively low compared to forced air systems.

CENTRAL FORCED AIR FURNACE

These units are mainly applied to residential heating and air conditioning systems. In addition to being able to force air to remote rooms with smaller ducts they can overcome the resistance of filters and provide an air supply during the cooling season. They are also often used in light commercial establishments. Consideration must be given to the air volume and total system resistance. Most manufacturers provide options which will yield higher static pressures when needed by a change in blower and/or motor.

FLOOR FURNACE

These next to room heaters are about the most inexpensive units to purchase and install as no duct work is involved. However, due to the hazard, especially to small children involved, it is recommended that other means of heating be considered. As there are thousands of them in use their service and maintenance must still be considered.

VENTED WALL HEATERS

These heaters have the advantage of requiring little or no floor space and are used for heating buildings, mobile homes and travel trailers. They have been used extensively in motel rooms so as to give individual control to the occupant. They may be of the gravity or fan type circulation.

VENTED ROOM HEATERS

This is the least expensive means of heating a room or several rooms if large openings between are available. The units are free standing and require only the hook up of gas, electric, (if fan type) and vent pipe. They are commonly regarded as a non-permanent attachment to the building and can move with their owner.

QUALIFICATIONS

In order to properly install, maintain and service any type of mechanical equipment such as gas fired heating units it is necessary that the Service Engineer be equipped with a sound working knowledge of the equipment he is dealing with as well as possession and knowledge of the physical tools he must use in order to properly accomplish his mission. Here again we should stress the fact that the Service Engineer must have much more than a mechanical knowledge of the equipment involved. The customer expects the modern Service Engineer to explain what he is going to do or has done, and in this day


of “do it yourself” is very likely to have a superficial understanding of the problem even if he is not able to solve it with his own hands. It should be noted that the lady of the house often knows more about the problem than the man as she has observed the symptoms over a wider range of conditions. At the level this section is studied and considering what the student Service Engineer has learned to this point there is no doubting his ability to handle the complexities involving elements of physics, chemistry, math and electricity.

In addition to learning to put these elements together in the heating field, certain physical tools are required. Besides the obvious tools used in mechanical trades, such as screwdrivers, drills, wrenches, pliers, shears, snips, hammers, hacksaws, etc., certain specialized equipment is required. This may be furnished by the employer or the Service Engineer himself. A job can be installed or inspected without these (visually) but in order to properly adjust or diagnose malfunctions they can be very important:

Portable apparatus for COA. 2 and CO determination.

Thermometers or potentiometer with a maximum reading of at least 600° F and a minimum of 0°B.

Volt-Ohm meter to determine correct voltages.C.

Amprobe to determine if current draw of equipment is normal.D.

Tachometer for measuring rpm.E.

Slope gauge for measuring low pressures; draft etc., down to .01 inches of water.F.

U-gauge for reading higher pressures such as gas line pressure in inches of water to the nearest .1 inch.G.

Velocity indicators may be revolving vane or deflecting vane. A pitot tube can also be used with a slope gauge. H. These devices are used to calculate air flow and to balance various runs.

Stop watch used for timing, tachometers, revolving vane, velocity indicators, gas meters, etc.I.

Copies of tables and formulas contained in this section which will enable Service Engineer to determine input from J. meter clocking and flue loss from the CO2 reading combined with the flue temp.

COMPONENTS OF EQUIPMENT

HEAT EXCHANGER

This is where combustion occurs as the fuel and air mix and burn. The end effect is transfer of heat of combustion to the exchanger walls where it is transferred to the circulating air by convection. The exchanger should be so designed as to admit cleaning tools if necessary. Some units employ a single drum type exchanger with a single port burner, others contain a multiplicity of combustion tubes with a multi-ported burner in each tube. Exchangers are subject to corrosion, cracking and clogging and are therefore a maintenance and service item. Materials will be discussed under selection of equipment.

BURNERS

Atmospheric burners may be single or multi-port type. Single port are less likely to clog as foreign matter tends to go on through and incinerate. Thus multi-port burners are usually more of a maintenance and service problem. Most burners are equipped with shutters to adjust the primary air drawn in by the gas jet as gas fuels vary in the amount of air required. Secondary air which is the air drawn in by the flame itself above the burners is not normally adjustable. In order to assure adequate air is mixed with the gas to complete combustion the equipment is designed to draw in an excess amount.


Power burners are supplied with booster fans which raise the gas pressure above line pressure and/or the combustion air pressure above atmospheric. These burners require more maintenance and service than atmospheric burners and are somewhat similar to oil burners.

CASING OR CABINET

The cabinet, which may be considered as a duct guides the circulating air to the blower and over the heat exchanger. Flanges are provided for connection to duct work for units so designed. An insulating lining is generally used to absorb sound and prevent loss of heat. As agency requirements regarding the maximum temperatures of surrounding combustible materials must be maintained a good reflective material is generally used. Removable panels are supplied for access to the components normally requiring maintenance or adjustment and for start up and shut down. Cabinets are subject only to occasional cleaning.

BLOWERS AND MOTORS

Squirrel cage, centrifugal blowers are used almost invariably in equipment which is designed for attachment to duct work which has a resistance to air flow or where the longest possible throw of free air is desired as in a unit heater. Propeller fans are used where there is little or no resistance to air flow. This type has the advantage of being quieter than the centrifugal type. It is important to remember that addition of restriction in a system served by a squirrel cage blower acts to unload the driving motor whereas in a propeller system restriction of the air flow through the system creates an added load on the motor. It is still a matter of choice what we call these types of air movers; fans or blowers. It is perhaps more common to refer to the centrifugals as blowers and to the propellers as fans. The air moving device may be driven directly by the motor shaft (direct drive) or through a system of pulley and belts (belt drive). Motors used need only enough starting torque to overcome bearing friction and inertia of the rotating parts as they do not become fully loaded until up to speed.

Appliances Located in Confined Spaces All Air From Outdoors.

Appliances Located in Confined Spaces All Air From Outdoors Through Ventilated Attic. Appliances Located in Confined Spaces. Ventilation Air From

Inside Building — Combustion and Draft Hood Dilution Air From Outside, Ventilated Attic or Ventilated Crawl Space.


The direct drive motors are usually 6 pole (1200 rpm synchronous speed) and are seldom used above 1/2 hp requirements. As a matter of economy and taking advantage of the low starting torque required, they can be of the shaded pole or permanent split capacitor type. These motors are well adapted to speed control by multiple windings or voltage control. This is particularly advantageous where the cooling air requirement differs from that of the heating cfm.

Belt drive applications usually employ split phase motors with capacitor start used above 3/4 and up to 5 hp switching to induction run when up to speed. Most residential units require 120 volt single phase. Light commercial applications are quite often 240 volt single phase. Three phase is not often encountered on light commercial jobs where there is no heavy duty equipment. In replacing a motor or capacitor the same electrical characteristics must be used. This includes the temperature rise at which the motor is rated. Totally enclosed motors must be used where there is any chance of molten material from a burnout falling on flammable material.

The subject of fans and motors will be discussed more fully under, Selection of Equipment.

CONTROLS

The basic components required to control a gas fired warm air system are a room thermostat for opening and closing the electric valve circuit on the unit as the demand for heat requires, a fan control for delaying start of the fan motor unit some heat is generated, a limit control which will cause the unit electric valve to close if the air supply becomes too low due to clogging of filters or closing of duct dampers or registers, a safety pilot which causes the unit electric valve to close if the pilot flame goes out and finally the electric valve itself which is wired in series with the safety controls and thermostat, admitting gas to the burners as heat is called for. Many room heaters are equipped with non-electric automatic valve which opens and closes as the temperature on its capillary tube and bulb change, the bulb being located in the return air grille.

Appliances Located in Confined Spaces All Air From Inside the Building.

Appliances Located in Confined Spaces All Air From Outdoors — Inlet Air From Ventilated Crawl Space and

Outlet Air to Ventilated Attic.


INSTALLATION

SIZING AND SELECTION OF EQUIPMENT

Many considerations are involved in the sizing and selection of equipment. It is sufficient to say here that proper performance and comfort are almost completely in the hands of the man who makes the heat loss calculations and lays out the system. Not only must the unit output be closely matched to the building’s heat loss to afford smooth cycling, but placement of the heated air must be considered carefully with regard to the location of the occupants.

SELECTION

Once sizing has been determined factors affected by the type of application must be resolved. Many factors are involved. First of all consideration must be given to the type of building involved and the use to which it is being put.

We have, to list a few, such applications as single and multi-story residences, apartments, auditoriums, bars, kitchens and dining rooms in public places, pool rooms, bowling alleys, churches, convention halls, colleges, primary and secondary schools, garages, airplane hangers, greenhouses, gymnasiums, small hospitals, motel, various light manufacturing or warehousing facilities, laboratories, libraries, museums, night clubs, offices, print shops, stores, supermarkets plus many other specific types.

Central units are most commonly used in single residential work. A gravity furnace located in the basement will do a good job in small homes, particularly two story as opposed to the spread out ranch styles. In larger and single floor homes forced air furnaces are required if the system is the central type. Where basementless, slab floor homes with space at a premium are involved down flow units may be installed in utility rooms or closets. Where head room is a problem, horizontal or lo-boy units are used. Ducts can be part of the slab or in the crawl space. Blower may be direct drive or belt drive depending on the air requirements. Consideration should be given to appearance, serviceability, cabinet size, reliability of equipment, location of replacement parts stocks, particularly motors and controls. And all these should be weighed against price. Remember, “The bitterness of poor quality lingers longer than the sweetness of a low price.”

Residences are also heated, but less satisfactorily by room heaters or wall furnaces.

In small stores unit heaters of the propeller type are very commonly used if it is possible to place them so they will not create discomfort to employees or customers. Head room is a very important consideration. Quite often small duct furnaces are installed over an office or laboratory. This can avoid a concentration of heat and air by dispersing the outlet registers properly. If floor space is available a floor mounted unit heater or forced air furnace may be used. In larger stores and supermarkets more of the above type units may be used although large units may be used. Many of the big supermarkets are going in for “central station” equipment with air being forced through gas fired duct furnaces or coils using steam or hot water. Door heaters are very important as the checkouts are usually near the entrance and exit vestibules. Unit heaters or horizontal furnaces can be used to direct a curtain of air over the doors or into ducts around the doors. Infra-red heat is used here but not as frequently as those just mentioned.

Apartment building heating is usually broken up so that each apartment has its own central forced air system. Many are served by units as small as 40,000 Btu per hour input. This is quite often because the owner wishes the tenants to take care of the operating costs, however, the maintenance of the individual units is the owners’ responsibility. For these jobs quietness of operation is highly desirable as the furnace is of necessity located close to the living and sleeping areas, with very short supply and return runs. Quite often the return is nothing more than a hole in the wall with a grill above the unit which is generally located in a closet off a short hall or sometimes in the bathroom.

LOCATING AND SETTING THE UNIT OR BURNER

There are many considerations to be observed before deciding where to locate the unit and what precautions to take to assure proper operation and conformance with installation codes.


In general the first consideration is safety followed by performance. Subsequent consideration is then given to economics or how to minimize the amount of material and labor required for the job. Where possible at least 18” clearance is needed for service.

The furnace used in a forced air central system should be located where it will least disrupt usable floor space. This naturally is in the hands of the layout man although he cannot possibly visualize all the details and many changes are often made by the ingenuous installer, for cost reduction in time and material. If cooling is involved the distance from a remote condensing unit should be checked against the manufacturers’ maximum allowable run of refrigerant lines and recommended tubing sizes for various distances. The distance from gas meter to the unit must also be considered and pressure drop in the supply line to the unit allowed for. Location of the chimney which is used to carry away the flue products must be within an acceptable distance of the unit, otherwise it may be necessary to provide power venting to overcome the loss of draft.

Gravity furnaces should be located as near to the center of the structure as possible as balancing of heat to the various rooms is not subject to control by dampering to anywhere near the possible with a forced air system.

Placement of unit heaters is much more critical from the performance – comfort standpoint. Various units will cover larger or smaller areas depending on the amount of air handled and its velocity.

It is very important that the units be installed in a level position. Some general comments are in order at this point. First, the manufacturer’s instructions and specifications should be carefully studied.

Many municipalities and some states have ordinances and building codes governing the specific details of gas equipment installation. Wherever local regulations are at variance with any instructions furnished the installer should follow local codes as he will be subject to inspection against these codes rather than the manufacturer’s instructions.

Units should be installed in a location in which the facilities for ventilating permit satisfactory combustion of gas and proper venting under normal conditions of use. It is necessary also for any heat buildup to be carried away from confined spaces. In a confined space, two permanent openings must be provided, one near the top and the other near the bottom of the enclosure. Each opening shall have a free area of not less than one square inch per 100° Btu per hour of the total input of all units in the enclosure, each opening shall not be less than 100 square inches. When units are installed in buildings of unusually tight construction, provision should be made to obtain air from combustion and ventilation from outdoors.

Detailed information covering types of building and construction and heating plant locations may be found in the United States of America Institute Standard, (new issues will be under the American National Standards Institute) “Installation of Gas Appliances and Gas Piping.” USASI Z 21.30 Current Edition. (Figures 64F54A, B, C & 64F55A & B).

When used in connection with cooling units the heating units must be installed on the upstream side of or in parallel with the evaporator coil to avoid condensation in the heat exchanger unless the heating unit is specifically designed and certified for use downstream from cooling coils. Parallel installations should have some air flow dampering arrangement to prevent chilled air from entering the heating unit. Manually operated dampers must be provided with a safeguard to prevent operation of either unit unless the damper is in the full heat or cool position.

As mentioned above “downstream” applications are permissible if unit is designed to resist the corrosive effects of condensate and arrangements made to collect and carry away the water formed to a place where it cannot harm the unit, building or its contents.

A pan with a drain line is frequently provided or recommended. The design of units certified by the American Gas Association Testing Laboratories per American National Standards has been tested at standard or reduced clearances to combustible materials. Standard clearances are usually 6” at sides and back, 18” front, 6” from flue pipe or draft hoods and 2” from the plenum. Reduced clearance units (commonly called closet or alcove certified) may have side and back clearances from 0”, 1, 2, 3, 4, or 5” as the manufacturer elects, provided he can meet the maximum allowable temperature requirements during testing. Front clearance is usually dictated by the 6” flue pipe allowable minimum clearance for single wall flue pipe, known as class “A”. Plenum clearances may be tested for 1”. In any event the front or any other side which must be reached for service need at least 18” for access for servicing regardless of combustible wall temperatures being below the allowable. Quite often a door in the heater space provides this clearance when open, particularly on central forced air furnaces located


in a closet off a hallway. Down flow units are subject to testing on combustible floors if this type installation is desired by the manufacturer. This generally requires use of a subbase designed and manufactured by the maker of the main unit. These bases are so constructed as to isolate the unit and outlet duct from the flooring and floor joists. This addition is of course unnecessary on concrete slab installations. Note–up flow units are almost invariably certified for use on combustible floors without a subbase. Horizontal furnaces are tested against jacket temperature requirements to certify them for attic installation. Clearances from flue pipes may be reduced by using special vent pipes which have been tested and listed for clearances less than 6”. For example B-1 signifies 1” clearance listing has been obtained.

In all cases the manufacturer’s clearance marking on the unit (usually on the rating plate) and his installation manual must be consulted. He will spell out how much room is required to remove certain parts and also warn that room is required for the service engineer doing the work. See Figure 64F56 for a typical clearance schedule on a central forced air up flow furnace.

These clearances are more common to central residential furnaces due to the premium on space in modern construction.

Figure 64F57 indicates another method of designating clearances in addition to other installation factors to be discussed later. This is a suspended blower unit heater. In addition to the foregoing, general clearance restrictions, garages and aircraft hangars require special attention. When overhead units are installed in commercial garages, they must be installed so that the bottom of the unit is at least eight feet above the floor. They shall be located in such a manner that the continued operation of the heaters will not raise surrounding combustible material above a maximum of 160°F. In aircraft storage or servicing areas, the heaters must be installed so that the bottom of the unit is at least ten feet above the upper surface of wings or engine enclosures of the highest aircraft which may be housed in the hangar. In shops, offices and other sections of aircraft hangars, communication with aircraft storage or servicing areas, they shall be installed not less than eight feet above the floor. Heaters shall be so located in all spaces that they shall not be subject to injury by cranes, movable scaffolding, aircraft or other objects. Provision should be made to assure accessibility of suspended heaters for recurrent maintenance purposes.

Figure 64F58A Figure 64F58B


Gas appliances may be installed on the floor of a residential garage provided a door of the garage opens on a level that is at or below the level of the garage floor or raised 18” or more above the floor. This is generally done anyway with the return air coming into a box or plenum under the unit. The purpose of these precautions is to get the flames above any pooling of inflammable vapors such as would result from spilled gasoline. Detailed information may be found in National Fire Protection Standards for Garages (no. 88) and on Aircraft Hangars (no. 409).

Conversion burners must be installed and adjusted in accord with the manufacturers’ instructions. This involves removal of previous firing equipment such as grates, stokers, oil burner, etc. A thorough inspection of the fire box and flue always is required at the time they are being cleaned preparatory to setting the burner. Adjustment of the draft must be made to compensate for the variations encountered in fire boxes and flue ways and insure safe and efficient operation.

In all installations the unit should be protected against physical damage due to bumping or exposure to moisture of indoor units. Accumulation of stored items around a unit should be carefully avoided as this may interfere with the flow of combustion and ventilating air to the unit as well as being a possible hazard from the standpoint of fire or injury to service personnel.

Areas subject to strong drafts should be avoided for indoor units. If this is not possible some sort of screen should be provided as the average indoor unit is not designed to maintain a pilot flame in a strong wind. In addition to possible pilot outages strong air currents can interfere with combustion air or cause flame impingement on the heat section with resultant shortening of its life. If the problem is intermittent such as might be created by opening of doors, an automatic pilot relighter should be considered as relighting of the pilot on an overhead unit involve considerable labor by the time a ladder is procured and returned. After the units are set and before going into operation they should be carefully leveled as flames tend to stay vertical and in case of a unit being out of level could seriously impinge on the heat exchanger walls thus shortening the unit’s life. Other results could be increased thrust on motor and blower bearings.

The following items have no bearing on locating the unit but should be checked even before moving the unit to its final operating position. This information will be found on

Power Exhauster.


the manufacturer’s name and rating plate which is required to be located in a place which is normally visible when servicing or connecting up the unit: (Figure 64F61)

Does type of gas shown on the plate agree with the fuel supplied at the site?1.

Does the Btu input and bonnet output equal or exceed that specified by the system designer?2.

Does the voltage phase and frequency marked on the plate agree with what is available?3.

Is the electrical protection and wiring suitable for the amperage marked on the plate?4.

If the model number does not agree with that specified the person who selected the equipment should be 5. consulted?

PIPING

Piping layout and sizing must be carefully planned to minimize cost and provide sufficient gas at the normal line pressures available. Connecting to existing lines serving water heaters or other appliances should be done with caution as the pipe serving them was probably sized for their input only. The new heaters or heater should in most cases be served direct from the gas meter or as close as possible with a new pipe. For convenience in servicing a shut-off valve and ground joint union should be provided at the unit ahead of all other controls. If liquefied petroleum gas (LP) is used a pipe thread compound resistant to petroleum solvents must be used. Piping should be sized on the basis of the table shown in Figure 64F58A whether a single run to a single unit or a trunk line supplying several units. The table is based on a pressure drop of .5” water column and a specific gravity of .60 for natural gas. Note air has a specific gravity of 1.0. Figure 64F58B shows multiplier to be used for gases with different specific gravities. Multiplier is to be taken times the volume of gas actually required for the unit. To find the volume of gas actually required, divide the appliance input rating by the Btu value per cubic foot of the gas being used. Note that while lp gas has a higher gravity than natural and requires a multiplier the Btu value is much higher which cuts down on the volume required. LP piping can be smaller than natural piping for a given input. Starting at the unit a pressure of approximately 7” w.c. should be available ahead of all controls including the appliance regulator. This means that supply piping when sized for .50” w.c. pressure drop would require a supply pressure of 7.5”. The local gas utility should be consulted for available pressure values. Example: a 240,000 Btu input model for 1000 Btu– .70 specific gravity gas, 200 ft. from utility should be consulted for available pressure values. Example: a 240,000 Btu input model for 1000 Btu–.70 specific gravity gas, 200 ft. from a 7.5” supply source.


Extensions to existing piping should conform to these tables. Existing piping should be converted to the proper size of pipe where necessary. In no case should pipe less than 3/4 inch be used. These tables apply to the average piping installation where four or five fittings are used in the gas piping to the appliance.

In some areas regulator vents (which allow regulator to work) and incidentally allow gas to escape if the diaphragm fails must be piped outside the building or into the area of the pilot flame where they would burn. Generally however vent limiting devices may be used which limit the escape of gas to a safe volume per hour. Most appliances now come equipped with such a device.

Piping must be adequately supported and a tee drop installed where chips or debris are likely to get into the controls.

Leakage checks in piping should be made with a soap solution, never with a flame. A complete system is usually checked by the gas utility which pumps air into the lines to a certain pressure, usually 6’ of mercury, which the pipe system must hold for at least 10 minutes. This should be done before any joints are concealed. Note that if piping does not meet this test the utility will keep the gas shut off at the entrance until defect is corrected. If the lines contain air they must be purged to pure gas. On small lines serving single units this may be done by disconnecting a pilot line and cracking the pilot valve. No system should be purged into confined spaces or areas where there is danger of ignition of the gas unless purging rate is carefully controlled. It is best to purge to a point outside the building. There have been many explosions due to purging inside the building. This usually occurred on new construction particularly where purging was done by personnel unfamiliar with handling fuel gas.

DUCT WORK

This phase of the layout work is generally done in an engineering office. The Installation and Service Engineer may be called upon to make the calculations and layouts but we must assume he had a good background in the subject before proceeding.

This discussion is intended to stress the idea that the installer should follow the plan as closely as he possibly can and consult with the layout men when he cannot.

Deviations, particularly reduction in sizes of duct work or too many turns will be manifest in insufficient air delivery caused by too high static pressure. This will result in inadequate heating or cooling plus operation of the unit on its safety limit control.

COMBUSTION AIR SUPPLY

If the units are installed in unconfined spaces infiltration usually provides sufficient air for combustion, ventilation of the unit and air for draft hood dilution. If construction is unusually tight this quantity of air outlined above must be obtained from outdoors. Not less than one square inch per 5000 Btu of total input is required for openings or ducts to outdoors. If exhaust fans or other items are drawing air from the space special attention must be given to replacing the exhausted air as well as supplying the air requirements for the unit. Otherwise a down draft will occur through the unit. In confined spaces as closets an opening near the top and one near the bottom must be provided, each having a free opening of 1 square inch per 1000 Btu of total input.

Here again reference must be made to Z21.30 - 1964, for details covering various installation, but it must be remembered that approximately 30 cubic inches of air per cubic foot of gas are required for combustion and draft hood dilution.


VENTING

Certified units are supplied with draft hoods if using atmospheric burners and venting of flue gases to the outside of the building is required on all units discussed in this section other than the units which are tested for outdoor use only. General requirements are that the vent pipe must be the same size as the outlet of the flue collector. Do not reduce the size of flue pipe or install a damper in it. Do not vent any other gas appliance into the flue pipe. Units should be vented directly into the chimney. Run the flue pipe from the draft hood to chimney making the run as short and direct as possible. Make all joints with the length nearest the unit overlapping the other and with pipe sloping upward toward the chimney. In some areas it is standard practice to install a drip tee in place of an elbow when excessive condensation is encountered. Unvented installations are never permitted. For details on various venting situations consult Z21.30.

Type B and BW vents permit reduced clearances in accord with their listing. Vents must be adequately supported for their design and weight so that there is no danger of disengagement.

Chimneys should be carefully examined to be sure they afford free flow and proper construction. Cleanouts must be provided.

If power venting is used manufacturers instructions for any piping involved must be followed.

In the event that the installer or layout engineer must select the power venter the following formula should be used:

Using cfm of flue products obtained above design the vent piping not to exceed 0.40” statis pressure. See Figure 64F59B for power venter.

WIRING

The majority of installations in this category will be 120 volt a.c., single phase and they are less frequently three phase, 108, 240 or 460 volts. Most units are equipped with transformers to reduce the control voltage to 120 or 24 volt from one of the above primary voltages. All units which bear the seal of testing agencies are marked indicating which type of power is required and what the maximum current draw is for the unit. This must be considered in sizing the supply wire to the unit and selecting overload protection for the wire and equipment itself. Local codes must be observed in selecting the type of wire. The National Electric Code should be followed in all cases not covered locally. The amp draw in the control circuit must be checked in order to set the thermostat heat anticipator. Most electrical equipment manufacturers distribute free handbooks which can be used for sizing wiring and circuit breakers or disconnects which may be needed or required. At this point we will limit our discussion to warning that inadequate wiring can constitute a hazard to the building and the equipment. Only by adequate sizing of wire can the unit get the required voltage for proper operation and life. Low voltage means shorter life. Naturally the voltage in question is read at the unit not at the panel as there may be a significant drop. BE sure to read instructions for installing thermostat for greatest comfort.

PLACING IN OPERATION

Once the gas piping, venting and wiring are in place and all connections checked and the air vented from gas line the unit may be lit off. Observe the following procedures:

See that all registers and dampers in supply pipes are open.

Check return grills to be sure they are not obstructed.


Set room thermostat well below room temperature. This protects against sudden ignition of the main burner if the unit is not equipped with so-called “safe lighting.” More than one service engineer has been startled into letting go of a ladder or jerking back against a pipe or other damaging material.

Remove burner or control access door and follow manufacturer’s instructions which appear near the controls. This generally involves first lighting the pilot which may on some units be done with a match, manually applied directly to the pilot burner, or at the near end of a flame carrying tube, on other units you may find automatic lighters which operate any time power is turned on and the pilot sensing device is calling to the ignition device to light the pilot, lighting may be accomplished by a spark or a glow coil or rod. The pilot sensing device will discontinue calling for ignition when the pilot flame has satisfied it. After the flame is established on the pilot it should be checked against the manufacturer’s instructions and adjusted if necessary. In case a glow coil is used for ignition, a pilot flame playing on it will cause it to have a very short life. Note that the majority of lighting devices function only when initial start up is made or when pilot is accidentally extinguished for any reason. Some units have intermittent pilots, however, which are ignited every time there is a call for heat by the thermostat. A few manufacturers use direct spark ignition of the main burner. A combustion of over 400,000 Btu per hour requires very sophisticated electronic flame safeguards and this is a subject in itself. See Figure 64F61 for typical lighting instruction and rating plate. Once the pilot is lit and adjusted the main valve may be opened and the thermostat adjusted to where it is calling for heat. At this point the main electric valve should open and the burner come on.

Check all connections with soap solution for gas leaks. NEVER CHECK FOR LEAKS WITH A FLAME. Now that the unit’s burners are firing the following sequence of checks should be made:

Within approximately 60 seconds the blower should start. If it does not the fan control, if of the heat-operated type, may be set too high. Turn the “on” setting down to where the fan will start. Normally this will result in a setting of approximately 125° turn on temperature. If a time delay relay is used to bring the fan on and the fan does not start check for proper wiring or defective control. When fan starts, check for proper rotation and correct if necessary. After a few minutes of operation check relief opening of draft hood to be sure all products of combustion are being carried to the chimney and not spilling into the room. Presence of flue products can be detected by a hot moist feeling on the hand or by introducing smoke into the burner and watching to see that it does not come out of the relief opening of the draft hood.

Pilot safety switch for 100 per cent safety shutoff shown in three operating positions.

Figure 64F62A


Check burners for proper alignment. The flame should not impinge on the heat exchanger surfaces. Color of flame and adjustment should be made per manufacturers instructions. Generally speaking the flame should be free of yellow because this can cause formation of soot. Too much yellow indicates there is not enough primary air and shutters should be opened. If flame is too hard, evidenced by a very blue appearance, with a pronounced noise, and possible lifting of the flame off the burners, the shutters should be adjusted toward the closed position as too much primary air is indicated. This condition can cause improper ignition and possible flash back of the flames of the orifices as the burner head can become overheated and light the gas under the burner head.

After about ten minutes operating the gas input should be checked. Turn off all other appliances connected to the gas meter. Check the time in seconds for the meter to run one cubic foot of gas. For greater accuracy ten cubic feet may be measured at the final setting. The Btu input may then be calculated by the formula below:

Input should be adjusted to within about 2% of the manufacturers rated input although it is permissible to fire at 20% under if the unit is found to be oversized for the heat loss at design conditions outdoors. Input is adjusted by turning the screw in regulator, in to raise input and out to decrease the input. Some manufacturers furnish an orifice size vs. manifold pressure chart for the unit. This should be followed and the meter checked after setting the indicated pressure. As greater comfort is obtained with longer burner “on” times the input can be reduced down to where the on cycles become longer but no lower than 80% of rated input is permissible. Ignition must be checked at any reduced input to be sure the burners still light across satisfactorily. It may be necessary to change orifices in order to get the reduced rate at a higher pressure if lighting is sluggish. The average unit is designed to operate between 3.0” and 4.0” w.c. manifold pressure. Method of calculating orifice sizes is shown below if this becomes necessary.

CONSTANT FOR ORIFICE CALCULATION


Example:

I = 43,200 Btu/hr.

h = 1040 Btu/cu. ft.

P = 29.2 + 3.3/13.6 = 29.44

S =.65

LP units are always operated at 11.0” w.c. Orifice sizes should never be changed by peening but only by accurate drilling. Misalignment of gas jet issuing from the orifice can result in failure to light across from one burner to the next or failure to inject sufficient primary air to the burner.

When rate is set check the temperature rise through the unit. The difference between outlet air and inlet air temperatures should be within the range shown on the rating plate. If cfm is required calculate the air volume by the following formula, this is essential when cooling addition is being considered or is already installed. Will also enable air changes per hour to be calculated for heated space.

The .80 represents the approximate efficiency of the unit and 1.08 is a factor containing .24 (specific heat of air in Btu/lb.), .075 (density of air in lbs./cu. ft.) and 60 (minutes per hours).


If air throughout is insufficient or too high, indicated by the temperature rise being too low or too high, volume may be changed by adjusting the motor pulley, turning to a larger diameter, increases blower speed of by changing speed tap on a variable speed motor. The amperage draw should be checked if a change is made. If a 40° C motor is used we can use a rule of thumb if the service factor amperage is not marked. Use 15% higher than full load amps. Note 50° C motors do not have a service factor. If motor is too far overloaded it will eventually burn out. Common causes of overload are too high a blower speed, moving too much air, too much system resistance requiring more power to get rated air, duct not connected at start up, low resistance fresh air intake and belt too tight. Be sure none of the speed taps are connected together as this can cause burnout. Filters should also be inspected as they are frequently filled with construction dust on new jobs. On belt drive units the belt tension should be adjusted so there is about 1/2 to 3/4 inch depression when pressed with finger in the middle. Motors are moveable to provide adjustment. Be sure the two pulleys are in alignment with each other.

Check function of fan control by determining outlet air temperature when blower stops after a burner on cycle of about ten minutes. Outlet air should be between 95 and 105° at cutoff. Control should come on within about a minute as previously discussed. These conditions can usually be obtained by using an “on” setting of about 125-130 degrees and an “off” setting of about 100°. Follow instructions if indicating other settings.

Check function of limit control by blocking return air. Control should shut off main burner before severe overheating occurs.

Check safety pilot by turning off all gas to main burners and pilot while hot. Within approximately two minutes the safety pilot device should act to close the main gas valve and also pilot supply gas if it is a complete shutoff unit. Note–all LP units should have complete shutoff as this gas is heavier than air and will not dissipate as quickly as natural gas. See Figure 64F62A For more complicated electric ignition systems consult instructions for checking.

ADVICE TO USER

First of all the instructions and other paper work accompanying the unit should be placed in a durable envelope near the unit after explaining the operating of the unit, what to expect, sequence of events, etc. In general the instructions will include points which can be interpreted as positive and negative. These should be explained. Some examples are as follows:

DO perform preventive maintenance on unit to insure better operation and equipment life.

DO leave pilot on during summer if heating unit only.

DO turn off pilot if air conditioning is installed.

DO replace or clean filters at beginning of each operating season. More often if found necessary. Check at least every 4 weeks.

DO oil-blower bearing before initial startup and every six months thereafter. Ball bearing type requires no lubrication.

DO follow motor manufacturers’ instructions on belt drive motors. In absence of such instructions, do oil before initial startup and every six months thereafter.

DO check belt condition and tension every six months. Allow 1/2” to 1” depression midway between pulley centers.

DO clean blower wheel at least once a year.

DO inspect heat exchanger and flue periodically for rust and corrosion when aerosol spray cans are used in the home.

DON’T leave pilot on during cooling season.


DON’T light pilot until you have read lighting instructions. FOLLOW THEM.

DON’T operate unit with dirty filters.

DON’T operate unit with blower door or filter access door off.

DON’T over-lubricate as it causes dirt accumulation on parts of unit associated with motor and blower.

DON’T tighten belt too much as it will cause excessive bearing and belt wear.

DON’T treat thermostat roughly as it is a sensitive temperature indicating instrument.

DON’T keep changing thermostat setting. Find one setting which gives adequate comfort and leave indicator at that point.

Once more it must be made clear that the installer or salesman should point out the minor things that the customer can handle, such as fuse or circuit breaker location replacement or resetting, built in time delays (in some cases used on main gas valve) blowers, power vent and other controls for which he should know the functions. Other examples of things the user should know how to take care of would be relighting of pilots, resetting of non-recycling limit controls which are sometimes used where a recycling control would permit dangerous heat buildup as could happen in a counter-flow or horizontal unit if the blower failed to start for any reason such as motor, belt or blower control failure. The thermostat should be explained as this can cause more dissatisfaction than any other component of the system. Many people labor under the misapprehension that the thermometer reading should match exactly the setting on the temperature selector portion of the thermostat. This of course would only be possible if the “on” and “off” had no differential. It should also be pointed out that the temperature at the thermostat is not necessarily the temperature of rooms in the building at all levels. Setting must be adjusted for comfort not temperature.

Be sure that your name and phone number are prominently displayed on the equipment or nearby.

PREVENTATIVE MAINTENANCE

PILOT

Most Pilots used today are of the non-aerated type (Figures 64F62B & 64F62C) meaning they use no primary air mixed with the fuel gas before ignition. This has been a great improvement in pilot cleanliness as any air borne lint or other material cannot get inside the pilot burner. In fact it is incinerated as it comes into the flame. However there is no device 100% immune to failure. Gas borne debris from the pipe lines can collect in the pilot or debris resulting from heat exchanger scaling could fall on the pilot. Therefore the pilot should be inspected at the beginning and midpoint of the heating season. If pilot flame is low with adequate pressure or distorted it should be removed and cleaned. Check orifice carefully. During the off season; the pilot should be turned off if it adds to a cooling load. In this case be sure any automatic ignition device is turned off as it would operate all summer and would burn out if the glow coil type. Always check ignition of main burners after pilot cleaning or adjustment.


FIGURE 64F62B — Cross-section of typical aerated pilot burners.

Cross-section of typical non-aerated pilot burners.

BURNERS

Burners are also subject to collection of debris and lint unless of the single port type inshot. Even these can accumulate some dirt in the venturi section. The slotted type burners are more prone to clogging at the heads and also are the most commonly used today, except for conversion burners. Inspect burners at the same time as pilots and remove and clean if necessary. It is often sufficient to turn the burners up and tap them lightly. If lint has accumulated a stream of water will usually take it out. Check ignition and flame appearance after reinstallation.


FILTERS

Check filters periodically especially at beginning of season. Ambient conditions will determine how often they should be cleaned, if cleanable, or replaced. A filter signal which operates off the air pressure change as dirt accumulates is available. Dirty filters can cause “no heat” complaints and overheating of the unit. Replacement filters must be the same size as those originally supplied or specified by the equipment manufacturer.

BEARINGS AND LUBRICATION

Motors and blower bearings should be lubricated in accord with manufacturers instructions which appear on the unit. If anything has happened that these instructions have become illegible or missing add about four drops of SAE #10 non-detergent oil to each motor oil cup at the beginning and middle of each heating season. Do not over oil motors as this can be worse than not oiling. Blower bearings require more oil and should be filled at the time motor is lubricated. Note that most direct drive motors are factory lubricated and seldom require reoiling. It is very difficult to specify a definite schedule as most motor suppliers make their relubrication schedule conditional on climate, usage and other variables which are hard to apply to any one job. Ball bearing motors and blowers are often sealed and cannot be and do not need to be relubricated. Those with grease fittings should be relubricated as manufacturer instructs.

Exploded View of Combination Gas Control.


MOTORS - CLEANING

Motors may in time accumulate dust and lint which has found its way through the filters. This can have a serious effect on the motor’s life as it depends on air flow over its case and through its windings for cooling. If the case is blanketed by lint and the air supply holes clogged the windings will exceed their allowable temperatures and eventually burn out. A vacuum cleaning tool is very effective or if not available the lint can be brushed off.

BLOWER

The blades in the blower or fan will in time accumulate dirt which destroys their ability to scoop and throw the air as their airfoil characteristic has changed from curved to virtually flat. It is easy to check for this condition by running a finger along one of the blades if wheel is not readily visible. If this condition exists the assembly must be removed and the blades cleaned with a stiff brush. Be sure all resulting loose dirt is removed from the blower housing before replacing in unit as it would be blown directly into the occupied space. At the same time end play should be checked and corrected to about 1/32”. Driver and driven pulleys should be checked for alignment.

BELTS

On belted fan units check belt tension for the 1/2 to 3/4 inch depression previously mentioned. Tighten if necessary. Listen for squeal on start up. This indicates belt is too loose or needs replacing. Remember that excessive tightness puts a strain on motor and blower bearings. Check inside of belt for glaze or cracks. Replacement may be indicated and doing so before complete failure may save the customer from an outage and emergency call later on.

VENTING SYSTEM

Check all piping for evidence of corrosion. Make sure there is no spillage of flue products from the draft hood relief opening after the unit has been on a few minutes. This can be done by feel or by using smoke. Failure of this test may indicate an obstruction in the venting system or a down draft.

Check cleanout in the chimney below the vent pipe entrance for accumulation of debris and remove if necessary. Sight up the chimney with a mirror if possible.

Clean and oil motor on power vent if provision for doing so is available. Check blower wheel for dirt and clean if necessary

HEAT EXCHANGER

Heat exchangers should be cleaned annually. Most commercial units today have corrosion resistant heat exchanger material specified, among these materials are 321 stainless, 409 stainless, ceramic coated steels, aluminized steel and other types of stainless. In spite of the durability of these materials in the presence of moisture none will have a satisfactory life span if subject to the action of acids produced by the reaction of certain chlorine and flourine bearing products. These are usually found in cleaning establishments and have become more and more common in the home due to the advent of so many products in aerosol cans which often utilize one of the refrigerants as a propellant. Where cooling is used in conjunction with a heating system a leak in a refrigerant line can create a corrosive condition in the heat exchanger. It is therefore urgently advisable to check for corrosion at every call and at least once at the beginning of the heating season.

Corrosion usually begins at the coldest area exposed to flue products where the water produced in the combustion process condenses and combines with any chlorides and fluorides present to form acids which attack the metal. Quite often the first evidence of this condition will be seen at the top of the heat exchanger or in the venting system. It can frequently be seen as a discoloration of a vent cap on the end of a vent pipe. There is little that can be done to prevent this type corrosion other than completely isolating the combustion air from the source of contamination. At any rate evidence of a crack or hole of any type in the exchanger is an indication that it should be replaced as continued operation could be hazardous due to leakage of the combustion tubes. A cracked or corroded heat exchanger will often have a visible effect on the pilot and main burner flames. They can also be detected by running a soft gas flame using tubing, inside the combustion chamber while the blower


is running. Smoke candles are also used to detect leaks in the heat section.

CONTROLS

Check thermostat for proper operation. Burners should cycle about six times per hour with the burner “on” period ranging from 100% at outdoor design temperature. If cycles are more or less frequent, the heat anticipator on the thermostat which creates artificial heat to prevent “overshoot” of the heat cycle should be adjusted to coincide with the ampere rating of the electric gas valve. Very little maintenance of a modern thermostat is required as the contacts are usually sealed. Thermostats, relays, fan and limit controls, electric valves, regulators, timers, etc., used today are pretty much maintenance free and beyond keeping dust and moisture off them will provide years of trouble free service. Contacts and coils used are usually inaccessible.

OVERALL CHECK OF CONTROL FUNCTION

Although we have said preventative maintenance is limited to the outer parts of most controls a periodic check of their function may prevent an outage at some inconvenient time and temperature.

These controls often give evidence of an impending failure by erratic operation and quite often gradually cease to function rather than failing abruptly. In this case replacement is indicated. An example would be a gas valve chattering. This could be due to the gradual breaking of an internal connection. Fan control calibration can drift after long years of cycling. This could manifest itself in premature shutoff and recycling (assuming that it had not done this during its early life).

The main gas should be shut off and relit after determining that pilot safety circuit opened and closed the electric valve. This will determine condition of the thermocouple or other heat sensing shutoff device. Check thermocouple or other sensing element for sooting and clean if necessary. Look for breaks, cracks, corrosion or an oxidized appearance. Replace if any of these conditions are apparent.

Limit control can be checked by blocking off air to unit while it is operating.

The gas pressure on manifold and the input should be checked as it is possible for it to change or be changed by the user. Any device which permits accumulation of dirt should be cleaned. Pilot pressure switches if used, should be operated by shutting off pilot gas and checking continuity through the switch. Switch should be open.

SERVICE

REPAIR AND REPLACEMENT

The following items are generally repaired or replaced but more often replaced as they are mass produced at a much lower labor cost than that involved in field repair. Repair is usually only undertaken on an emergency basis. Of course we can consider the replacement of components on major assemblies as a type of repair.

ELECTRIC VALVE

3C for schematics of individual electric valves and the combination type. Figures 64F65 & 64F66 for a combination valve and its components. The combination valve may have the main gas shutoff, pilot cock, pilot filter, pilot adjustment, main gas regulator, safety shutoff, modulation of input and main manual shutoff. Another combination control is shown in Figure 64F67A. The electrical main valve may be controlled by a solenoid diaphragm or heat activated bimetal strip. The latter type needs about 15 seconds of power to open. Most of the combination valves are built so that any of the major components can be replaced by the service engineer. It is also possible to remove and clean the manual and electric valve seats. A plain electric valve body can usually be left in the gas line and a new power head installed to replace a defective one. It is very important that when making up controls in a pipe line that a strain is not put through the body of a valve as it may cause leakage.


Figure 64F63A – Schematic Cross-Section of Combination Main Gas Valve and Pressure Regulator, Showing Sensing Regulator to Control Main Outlet Pressure.

Figure 64F63C – Cutaway View of Solenoid Valve.


Combination Gas Control combines a manual main and pilot gas valve, a separate automatic safety pilot valve, pilot adjustment valve, pilot and bleed gas filtration and an automatic electric valve into a compact combination control.

REGULATORS

Generally the only part of a regulator that fails is the diaphragm. On ordinary appliance regulators the best course is to replace the entire regulator. A clogged vent orifice can cause sluggish and erratic regulations as the air above the diaphragm must move in and out as the diaphragm moves to regulate the pressure in the gas line. Always check the inlet pressure upstream of the regulator if the correct manifold pressure cannot be obtained or maintained. It should be between 7” and 14” w.c. Clean the vent orifice if clogged. Check with the local gas company if the inlet pressure is too low, too high or pulsating. See Figure 64F63B & 64F67B for a view of a typical appliance regulator.


Schematic Cross-Section of Gas Pressure Regulator.

Typical Appliance Gas Pressure Regulator.

HAND SHUTOFF VALVE

This item is seldom a source of trouble unless it cracks. Lubrication may be necessary if the handle is extremely hard to turn.

BLOWER RELAY

The function of this control is to by-pass the unit’s fan control when a cooling coil is used on the furnace. They are sealed at the factory and the only remedy for a defective one is to replace it. Be sure the amp rating of the contacts are equal or higher than the end one. On many units the relay and control transformer are a single assembly. (Figure 64F48)


PILOT

Beyond occasional cleaning pilots will usually give many years of trouble free operation. However, excessive temperatures can oxidize the head or thermocouple necessitating replacement of one or both. Again original equipment pilot should be used as various designs are available as they are nearly always non-interchangeable due to need to position flame near burners and cross lighter.

BURNERS

If clogged to any degree at all they must be cleaned as stoppage of the burner ports will cause the gas to light back at the orifices and could burn out the wiring and damage controls. If deteriorated to any extent, burners should be replaced.

FILTERS

Replace with new ones of same size or clean if only moderately coated with dirt. Wash reusable filters as instructed by manufacturer. Check position of indicator on electronic filters and clean if necessary.

BLOWERS

Check for dirt on blades of wheel and on motor. Clean if necessary. Lubricate if scheduled or appears necessary. A defective motor should be replaced with the same size or larger, never smaller. Be sure all leads are reconnected per unit wiring diagram. If multi-speed reconnect as originally wired unless originally miswired. Replace defective belts with the same size and adjust to proper tension. Blowers do not often require replacement parts other than an occasional bearing failure. If a wheel fails it may indicate excessive speed.

HEAT EXCHANGER

Examine and clean before each heating season. If any cracks or corrosion or holes are found, replace the exchanger.

VENTING SYSTEM

Clean if necessary and replace any corroded flue pipe.


Simplified Sketch of Heating System and Operating Controls.

Ladder Diagram of a Relay Used to Control a Blower Motor For Both Continuous and Automatic Duty With a 24 Volt Transformer.


TROUBLE SHOOTING

See typical heating wiring diagrams, Figures 64F68A & 64F68B.

Service calls may be occasioned by one or more of the following problems (See Figure 64F48 for components of a typical furnace.)

Many good handbooks such as “Baso Service Manual” and Honeywell “Gas Burner Controls” Vol. I & II are available upon request and should be consulted for more detailed instructions.

NO HEAT

May be caused by power failure in primary or secondary circuit or gas supply failure to or in unit. Initial checks should be made for pilot flame, broken belt or idle motor, check thermostat setting which may be low, check for false heat at thermostat such as radio, lamp or other devices which give off heat. Check heat anticipation setting on thermostat (Figures 64F69A & 64F69B). If none of these items are at fault proceed as follows:

FIGURE 64F69A — Schematic Diagram of Thermostat With Heat Anticipator in “ON” and “OFF” Position.


FIGURE 64F69B — Schematic Diagram of Thermostat With Variable Anticipator.

Check primary source of power for failure using meter or test light. This would be the 120, 240 or other higher voltage feeding the unit from the main circuit branch box.

Check output of secondary if control voltage is other than line voltage in which case a step down transformer is used, usually 24 volt secondary.

If sufficient power is available in control circuit check for flow of current through the thermostat with contacts closed. Note–A low supply voltage can result in insufficient power to open the gas valve or start the fan motor.

If furnace is hot, jumper the limit control. If burner comes on, limit control cycling is indicated. May be due to overfiring of supply air restriction. If furnace is cold power flow through limit control should occur.

If power is available to coil of electric valve and within 10% of rated voltage valve should open, provided safety pilot system is functioning.

Check for flow through contacts if a pilot switch is used. If safety is built into gas valve check output of pilot thermocouple in millivolts per manufacturers instructions.

Check sail switch in exhauster if used. This switch is used to prove the unit is venting, switch is in series with gas valve and other safety switches.


If unit is found to be operating satisfactorily but will not hold the thermostat setting either the unit is too small for the heat loss or the input on it is incorrect. Although the flue loss of factory designed equipment is well controlled in the design itself and certified by test there is no harm in checking it. Take temperature in the flue about 4’ from the draft hood, enough to get a good average. Take a CO2 reading at the same point. Subtract the room temperature from the flue temperature to get flue temperature rise. Using nomograph and a straight edge, see Figure 64F69C pick off the flue loss. Loss should not exceed 24% to 26%. Causes for excess flue loss could be excess draft, insufficient air moving through the heat exchanger to pick up the heat and carry it to the heated spaces or displacement of a critical part of the furnace. A unit which is oversized for the job and is operated below the design input will show a flue loss exceeding the above.

HIGH FUEL COST COMPLAINTS

It may be that the customer has the wrong impression of what the fuel cost should be. In many cases it will cost more than other fuels he has previously used. Here he is paying for convenience and comfort. He should be instructed on how to read his meter and told what he is paying for the gas he uses. The utility can be of great help on this problem. Dirty and poorly adjusted equipment can cause higher bills. Living habits of the occupants and many other factors can enter this problem.

If it is found that limit control has been cycling, check for motor operation. If motor will not operate when unit is hot turn fan control to lowest “on” setting. If motor doesn’t run jumper fan control. If still no motor operation and power is available at motor, repair or replace motor. Motors will sometimes freeze due to lack of lubrication and can be freed by oiling. A capacitor replacement may sometimes solve this problem. If motor is operational check for air supply failure due to dirty filters or air conditioning coil. Check for insufficient air by measuring the temperature rise through the unit. Should be within range specified on rating plate, examples 70° to 100° and 45° to 70° rise check gas input for overfiring. If all else is correct, replace limit control (Figure 64F70 shows electrical symbols which will be of value in reading wiring diagrams).


FIGURE 64F70 — Recommended Simplified Graphic Electrical Diagram Symbols.

COLD DRAFTS

Check for proper fan control setting. It is possible on some systems that discharge air below 100° will feel cold to some people. If this is the cause adjust the “off” setting to a higher point. May also be due to poor layout or too much air (low temperature rise of the supply air).

FALSE FAN CYCLING

Increase the differential, that is the difference between the “on” setting and the “off” setting. On the average 100 to 130° on and off settings will usually give the best results, on well designed equipment.

ODORS OR CONDENSATE

Check for gas leaks if strong odor is noticeable. Condensate or a characteristic odor of combustion indicates the unit is not venting properly and flue products are spilling out the draft hood relief opening. Check for flue obstructions or a hole in the pipe to chimney.

Look for defective heat exchanger. Check for electrical failure. On a new job residual oil on the heat exchanger or in pipes can be the source of odors. Also check for lack of combustion air.


EXCESS NOISE CAN BE DUE TO:

Fan, belt, bearings, motor, etc. Adjust end play of blower shaft, look for loose blades or wheel rubbing against housing. Check motor for hum or rubbing against housing. Check motor for hum or growl; may require lubrication or replacement. Low voltage often causes noisy operation of motor. Flame noise is usually an indication of too hard a flame. Can be reduced by reducing shutter opening to restrict primary air.

A loose motor will be noisy. Tighten mounting bolts.

Transformer hum can sometimes be stopped by striking with a center punch or hammer. Loose laminations are the cause and the transformer usually must be replaced. Heat exchanger noises are not often removable. May be due to oil canning of large surfaces or tickling of joints. It would be well to suspect cracks if a pronounced slow ticking is heard.

Duct vibration can be stopped by adding stiffening angles.

Air noise in the ducts due to high velocity can be helped by insulating the ducts with fiberglass batting.

INSUFFICIENT HEAT

In some rooms insufficient heat may be due to some rooms getting a surplus of the available heated air. This condition can only be remedied by balancing, using dampers in the supply pipes. In some cases it may be necessary to make additional runs of supply or return ducts.

EXPLAINING

When the initial installation is completed the customer should be shown his owner’s manual and warranty and both carefully explained. The DO’s and DON’TS must be covered and explained. As people are getting more technical minded every day it would be well to explain the function of each component and point out the features he has obtained by buying your equipment. It would be well to advise him that the Btu input and output determines the ability of the equipment to maintain a selected indoor temperature at the outdoor design temperature. Explain efficiency in terms of input, output, flue loss and jacket loss if unit is not in the heated space.

Explain temperature rise through the unit and how this goes up as the air flow goes down (due to dirty filter, belt slip, etc.) until the unit cycles on the limit control and will no longer heat the space properly. Inform him as to where you can be reached in case he prefers you do all the preventative maintenance as well as servicing.

In cases involving service of any type carefully explain beforehand what is required and how much it will cost him. Upon completion of the service go over it again and leave any defective parts with him unless the warranty requires their return or he does not want them to check up on you.

residential and light commercial gas-fired heating ... · residential and light commercial...

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