weston basic duct sealing doe - weatherization. weston...zone like a ventilated attic or crawl space...
TRANSCRIPT
Basic Duct Sealing
– Lil Weston, Rappahannock Area Agency on Aging –Fredericksburg, Virginia
By attending this session, participants will:
• Identify health and safety issues involved with sealing duct systems;
• Gain a fundamental understanding of the importance of duct sealing;
• Identify different types of duct systems and design (flex, metal, duct board, floor panning, etc.); and
• Become familiar with the materials and tools necessary to properly seal duct systems.
Why do ducts need to be sealed?
• The air in ducts is moved by a powerful fan. Duct leakage can create pressure imbalances in the building envelope, causing combustion safety issues and comfort issues.
• Duct leakage outside the building envelope decreases the efficiency of the entire HVAC system.
• Duct leakage can cause moisture and mold problems. Leaks in return ducts can draw in air from the attic, crawl space or attached garage.
Master Bedroom
Bedroom Bath
Utility Kitchen
Living Room
Whole House Return in Hallway
Supp
ly
Supply
SupplySupply
Supply Supply
Supply
Supply
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Closed doors that prevent supply air from getting back to a return cause positive pressures in those rooms...
meanwhile starving the return for air, causing negativepressures in the zone where the return is located
DuDuct lct leeaakkagageecan cause the same problems
Combustion Appliance Zone (CAZ)
• Air sealing or duct sealing may affect combustion-appliance venting by increasing house pressures or reducing the available supply of combustion air.
• After all weatherization materials have been installed, all crews or contractors must conduct worst-case draft testing and check the safety of all combustion appliances.
Combustion Appliance Zone (CAZ)
Return at furnace contributed to CAZ problem: -8 pa
Gas water heater and clothes dryer in same room
Replaced solid door with louver door – CAZ went down to -4 pa
Air Leakage Requires All of the Following:
•Air •Hole •Pressure Difference
1 cfm in = 1 cfm out
Air Moves from High Pressure Areas to Low Pressure Areas
Air Moves through Ducts at a High Pressure Relative to the Outside of Ducts
Ergo…
A hole in a duct leaks more air than the same size hole in the building envelope because the pressure difference across the hole in the duct is much greater.
Conditions Necessary for Mold Growth:
•Mold Spores Present•Available Nutrient Base•Temperature Range: 35° to 120° F•Relative Humidity of 70% or above at surfaceDuct leakage can increase the relative humidity inside the building envelope, crawl space, or attic enough to encourage mold growth.
Condensation at leaky duct/wall connection during cooling season
Quantifying Duct Leakage
• The amount of duct leakage can be determined by using a calibrated fan such as the Duct Blaster.
By itself, measures total duct leakage.
Used with the blower door, can isolate duct leakage to outside, supply leakage, and return leakage.
Finding Duct LeakagePressure pan testing with the blower door will help to find the biggest leaks.
Reversing flow on the blower door (pressurizing the house) is a good way to find leaks outside the building envelope.
A digital camera or a “see-snake” is useful for looking inside the ducts.
Finding Duct Leakage
Blowing smoke through a closed system helps to visually find duct leakage
Prioritizing Duct Leakage
• Ducts located outside the thermal boundary or in a buffer zone like a ventilated attic or crawl space should be sealed.
• Leaks closer to the air handler are under higher pressure and are more important than leaks further away
Prioritizing Duct Leakage - in relative order of importance
• Seal all return leaks in the combustion appliance zone to prevent this leakage from depressurizing the combustion zone and causing backdrafting.
• Plenum/air handler connection.• Connections at branch takeoffs, especially the tabs. • Joints in elbows.• Connections to boots.• Floor/wall/ceiling-to-boot connection
Prioritizing Duct Leakage - Beware!
• Floor and ceiling cavities used as return-air plenums. If possible, replace these with a duct and a filter grill or a grill straight off the furnace.
• Any building cavity used as a supply duct. If possible, replace these with a duct.
• These are nearly impossible to seal because you can hardly ever access all the framing details connecting these cavities to the outside.
Sealing a building cavity used as a duct
Entire cavity painted with mastic
Sealing a building cavity used as a duct
It’s always good to have a tall skinny guy on the crew for those hard-to-get-to places.
Sealing a building cavity used as a duct
Entire cavity painted with mastic
Panned return
Panned Return
Prioritizing Duct Leakage – Mobile Homes• Base of furnace closet where furnace is seated over duct.• End caps.• Boot/duct and boot/floor connections.• Crossover ducts in double-wide mobile homes.• Branch lines.• Ducts connecting outdoor unit for central cooling.• Plumbing/electrical penetrations.• Belly returns should be closed off.
Typical Existing MH Furnace/Duct Connection
Sealed (from inside) MH Furnace/Duct Connection
Mobile Home – sealed register with boot
Prioritizing Duct Leakage – Small MultiFamily
• Party walls and between-floor joist spaces are usually very connected to the outside, so duct leaks in those areas are difficult to seal.
• Ducts are often run in drop ceilings and soffits, but those are often open or connected to the outside.
Prioritizing Duct Leakage – Small MultiFamily
This whole closet is the return plenum
Would you want to circulate what is in this closet throughout the apartment?
Note condensation from line that runs to outside HVAC unit
The zonal pressure in this cavity is 42 pa
Prioritizing Duct Leakage – Small MultiFamily
Prioritizing Duct Leakage – Small MultiFamily
Panned supply ducts in crawl space
Pressure Pans
39.5 pa
Prioritizing Duct Leakage – Small MultiFamily
Register in upstairs apartment-gap between duct and wall
Pressure pan-
38.7 pa
Prioritizing Duct Leakage – Small MultiFamily
This is the “duct”
Sealing Ducts - Materials
• Joints should rely on mechanical fasteners to prevent joint movement or separation.
• Tape should never be expected to hold a joint together nor expected to resist the force of compacted insulation or joint movement.
• Aluminum foil or cloth duct tape are not good materials for duct sealing - their adhesive often fails after a short time.
Sealing Ducts - Materials
Duct mastic is a preferred duct sealing material because of its superior durability and adhesion.
Apply at least 1/16-inch thick and use reinforcing mesh for all joints wider than 1/8 inch or joints that may experience some movement.
Using mastic to seal ductwork
Using mastic to seal ductwork
Using mastic to seal ductwork
Using mastic to seal ductwork
Return in ceiling
Using mastic to seal ductwork
Return in ceiling-sealed
Sealing Ducts - Materials
Two-part foam may be used to seal ducts in unconditioned areas.
Two-part foam insulates as well as seals, saving time.
Crew should wear respirator when applying two-part foam in poorly ventilated areas.
Sealing Ducts - Materials
Using two-part foam to seal ductwork
Using two-part foam to seal ductwork
Sealing Ducts - Materials
Using two-part foam to seal ductwork – one product to seal and insulate ducts and walls
Sealing Ducts - Materials
Sealing Ducts - Materials
Take care to get total coverage when using two-part foam to seal ducts –sometimes it is better to use mastic to seal when the hand fits and the foam gun won’t go.
Sealing Ducts – Duct Chases
If chase opening is large, seal with a rigid barrier such as fire-rated foam board, plywood or drywall, and seal the barrier to ducts with caulk or foam.
Smaller cracks betweenthe barrier and surrounding materials may be foamed or caulked.
Sealing Ducts
• Flex-duct-to-metal joints: • Apply mastic to the metal sleeve • Clamp the flex-duct’s inner liner over this strip of mastic
with a plastic strap, using a strap tensioner.• Clamp the insulation and outer liner with another strap.• Support ducts with duct hangers to take the weight off the
joints.
Using mastic to seal flexduct
Take-offs/connectors should be mechanically fastened to trunk
Using mastic to seal flexduct
Mastic should be applied to connector, then the duct slipped over the connector
Using mastic to seal flexduct
Duct should be secured with a strap.
Fiberglass mesh tape should be used on connections with a wide gap or junctions which may experience movement.
Using mastic to seal flexduct
Mastic may applied using a brush or by hand
Using mastic to seal flexduct
Insulation may then be pulled down, then secured with another strap
Sealing Ducts - Panned returns (or supplies)
• Mechanically fasten pan to joist if needed.• Seal all edges and seams of panning material, including
connections to ducts, or main trunk.• Seal top of joist where it connects to the sub-floor. Gaps in
the sub-floor must be sealed if present.• Seal all accessible seams and connections from the return
inside the house.
That’s all folks!
Thank you for coming!
Duct Demonstration in Exhibit Hall
Block 5 – Wednesday, 2:00-3:30pm
Block 8 – Thursday, 10:15 – 11:45 am