94 FINE HOMEBUILDING

iking’s largest gas kitchen range isa 5-ft. long colossus with six burn-ers, a griddle and a char-grill that

collectively can throw off 123,000 Btu ofheat—enough to warm a small house in acold climate. Not many at-home cooks willtax that kind of range to its limit, but profes-sional-style cooking appliances with high-output burners and amenities like grills andgriddles are more common than ever. Rangehoods capable of whisking away the smoke,grease, moisture and combustion gases mustbe correspondingly robust, drawing as muchas 1200 cu. ft. of air per minute (cfm).

At the other end of the scale are what manyresidential cooks continue to use: four-burnergas or electric ranges generating one-third theheat and fewer air contaminants. Althoughany standard range can smoke up a kitchen,vent hoods drawing as little as one-tenth thevolume of air—and costing one-tenth theprice—may be enough.

Why do I need a hood?No matter what the range or cooktop,kitchen designers, appliance manufacturersand building scientists all suggest it be usedwith a range hood. Research at Broan-NuTone,a manufacturer of kitchen-ventilation equip-ment, suggests that in addition to obviousspatter, steam and odors, cooking producesunseen hazards. Tiny particles of grease less

V

Range

HoodAll you need toknow to pick theright kind, not the right brand

Choosing a

BY SCOTT GIBSON

than a half-micron in size can float in the airfor days. Electrostatic forces, air currents anda phenomenon called thermal plating drivegrease into fabrics, cabinets and wall surfaces.And as more rigorous building practices cre-ate tighter houses, air contamination becomesa health as well as an aesthetic problem.That’s because those drifting grease particlesare nutrients for microorganisms such asmold and bacteria.

From small to large, a vent forevery cooking style and applianceThere are nearly as many kinds of rangevents as there are ranges. At the low end,some selling for as little as $30, are simplehoods with low-powered, self-containedblowers (photo 1, below). Downdraft andslide-out vents are hidden when not in usebut deploy when needed (photo 2, below).Over-the-range microwaves double as venthoods (photo 3, below). Chimney-style hoodsmount on the wall and become a design ele-ment in the kitchen (photo 4, below). Ceiling-mounted units are designed for cooktops andranges located away from a wall (photo left).At the top end in terms of size and perfor-mance are professional-style hoods with pow-erful blowers that may cost $5,000 or more.

Many low- and mid-range hoods can be in-stalled as recirculating fans that are not vent-ed to the outside (sidebar p. 98). Others can beset up so that their blowers aren’t even in thekitchen at all but mounted in the duct itself

or in a wall- or roof-mounted terminal fitting.Duct sizes vary with the capacity of the blow-er (sidebar p. 96).

Two ways to calculate how muchairflow you needThe higher the potential for cooking conta-minants—that is, the more heat the range canproduce—the bigger the blower the manu-facturer will recommend. There are, howev-er, no absolutes in sizing a range hood andblower. Dale Rammien, director of the HomeVentilation Institute (HVI), an industry tradegroup, says the minimum for a wall-mountedrange hood should be 40 cfm per lin. ft. ofrange. A range on a kitchen island or penin-sula needs 50 cfm per ft. of range.

“There is a lot of cooking that is nicely ven-tilated with 100 cfm,” says David Wolbrink,vice president for research and developmentat Broan-NuTone. Although minimums maybe enough, modestly powered range hoodsare designed for modest cooking demandsand basic four-burner 30-in. ranges. Cookswho favor the high-temperature cookingstyle that produces a lot of smoke and greasewill be disappointed.

With higher heat output and larger rangesizes come higher-capacity blowers and larg-er hoods. Robert McBride, senior productmanager for cooking and ventilation atViking Range Corp., says the industry oftenuses the 100-to-1 rule: For every 100 Btu ofheat generated by the range, the blower

3 Microwave vent

Downdraft2

4Chimney-style,wall and island

Basic, self-contained

Range hoods are available in anumber of styles and blowercapacities. 1. Basic, self-con-tained hoods house a fan mo-tor and grease filter, and arethe most economical option. 2. Downdraft models drawcooking contaminants from be-hind the range or from themiddle of the range top. 3. Mi-crowave ovens mounted overthe cooking surface also candouble as range hoods, al-though they are less efficientat gathering smoke and steamthan other types. 4. Chimney-style hoods are mountedagainst a wall or an island.

AIR SCOOPS: BASIC AND BEYOND

1

Photos this page: 1. Courtesy of Broan-NuTone; 2. Courtesy of Faber; 3. David Duncan Livingston; 4. Courtesy of Viking.

96 FINE HOMEBUILDING

should move 1 cfm of air. That means a gasrange with four 15,000-Btu burners should beequipped with a 600-cfm blower. Those num-bers are a starting point. Downdraft and islandinstallations may need more powerful blowers.

Not all cooks need high-capacity blowers.“Yes, if you have a pro range that has all thatstuff on it, and it’s 48 in. wide in a hugekitchen, you might want to go with that high-er cfm,” says Wendy Holdsworth, marketingdirector at Faber, an Italian manufacturer.“But people got brainwashed and are doingthe higher cfm with every application, and it’sreally unnecessary.”

Another potential problem with high-capacity blowers is backdrafting.

Just as important as sizing the blower cor-rectly is using it properly. Many manufactur-

ers say the blower should be running beforea single burner is turned on—not when a hotpan is making lots of smoke. Running theblower first sets up a good flow of air andboosts efficiency.

Installation height and hood shapeaffect performanceManufacturers make their own recommen-dations on how high the hoods should be lo-cated over the cooking surface. In general,mounting height falls in one of three ranges,depending on the size and capacity of theequipment. Small, low-powered hoods typi-cally are installed 18 in. to 24 in. off the cook-ing surface; midsize hoods, 24 in. to 30 in; andhigh-capacity, professional-style hoods, 30 in.to 36 in.

Sleek, low-profile island hoods are designed to minimize visual interference. The trade-offis a smaller capture area for cooking contaminants. That’s a problem for high-temperaturecooking styles that produce a lot of grease and smoke. Photo courtesy of Faber.

Even island range hoods with powerfulblower motorsmay not be ableto overcomekitchen cross-drafts. Mountingthe hood closerto the cookingsurface andreducing draftscan help. Roof-mounted blowerscan reduce vent noise.

Downdraft units are unobtrusive butmay not be as efficient as other stylesin some situations. Models mounted atthe back of the range can have troublepulling vapors from the front,especially when a tall pot is used.

I SLAND BREEZES

Manufacturers recommend specificduct sizes for the models that they

make. One of the first rules of thumb is to take their advice seriously.The industry generally suggests running the same-size duct allthe way from the range hood to the fitting on the wall or roof.Transitions to smaller sizes make it harder for the blower to

function efficiently.

Terminal vent

Vent

Filters

HOOD

DOWNDRAFT

Duct: Keep it short

Drawings: Brian Jensen

Most cooks, especially tall ones, are morelikely to increase the distance between thecooktop and the hood to make food-tendingeasier. When deciding where to mount ahood, Holdsworth suggests making a card-board template of the hood and taping it tothe wall. If the installation seems too low, theunit can be moved up. But manufacturers arecareful to recommend against exceeding de-sign maximums. Even pro-style hoods mount-ed higher than 36 in. won’t work as well.

The same goes for cooking alcoves. Thinkof one as a large hood. Its opening should notbe much higher than 36 in. above the cook-ing surface, and the ceiling shouldn’t be muchmore than 18 in. above that.

Hood shape also is a big factor in per-formance. Pro-style hoods not only gen-erate toupee-lifting air currents but alsohave cavernous interiors, some 18 in. deep.These hoods have high capture efficiencies:a large area beneath the hood wheresmoke, grease and moisture are trappedbefore the blower pulls them away. In-dustry experts say the best performancecomes from hoods that match the foot-print of the cooking surface in width anddepth. Even better is a hood that extendsbeyond the sides of the cooking surfaceslightly (drawing p. 98).

Range hoods are highly visible, andmanufacturers have taken pains to makethem as attractive as possible. In fact,studies show that consumers are most inter-ested in what the hood looks like, not howwell it works, says Brian Wellnitz, productmanager at Broan-NuTone. The result is anumber of designer hoods with low, sculptedprofiles or nearly flat shapes. They are popu-lar on island installations because they don’tblock the view of the rest of the kitchen. De-pending on blower size and cooking prefer-

ences, designer hoods may work fine, butthey are not as effective at capturing contam-inants as more conventionally shaped hoods.

Downdraft and islands: two ventilation problemsDowndraft ventilation systems are an attrac-tive option for anyone who doesn’t want tolook at a range hood. Some ranges are built

with vents integrated into the cooking sur-face. Other manufacturers make a type ofdowndraft vent that pops up at the back ofthe range when in use and retracts when notneeded. Although downdraft models can beeffective for many cooks, they also are fight-ing the laws of nature.

Rear-mounted downdraft units work bestfor shallow pots and pans on a back burner;

30 in. to 36 in. High capacity (professional)

24 in. to 30 in. Midsize

18 in. to 24 in. Small, low-powered

INSTALLATION HEIGHTS

Professional-style hoods with large capture areas are designed to handle thehigh cooking temperatures typical with professional-style ranges. The hood trapssmoke, grease and odors, giving the blowertime to expel contaminants. Photo courtesy of Faber.

Minimum duct size is usually 31⁄4 in. by 10 in., the equivalent ofa 6-in. round duct. Large-capacity hoods may need an 8-in. or10-in. round duct. It should be made of metal.

Second, the industry says, keep the duct run as short and asstraight as possible. Just about any blower should be able tohandle a run of 30 ft. and turn a few corners. But too manytwists and turns slow down airflow. Installing a single 90° elbow

is the equivalent of adding 5 ft. to 10 ft. of straight duct. Back-to-back 90° elbow should be avoided altogether.

Last, buy a good-quality terminal fitting, the piece that goeson the wall or roof, preferably from the same company thatmanufactured your hood. Cheap fittings increase static pressurein the line and cut performance.

—S. G.

FALL/WINTER 2002 97

Manufacturers specify mounting heights above thecooking surface. In general, as hood size and blowercapacity increase, the higher the hood can be installed.

98 FINE HOMEBUILDING

however, these units have more difficulty cap-turing moisture from a tall pasta pot boilingon a front burner. One option is to bump upthe cfm rating of the blower, says Linda Eber-le, a designer with Dream Kitchens in Madi-son, Wis. If a range normally would be pairedwith a conventional 300 cfm to 600 cfm hood,she says, a downdraft model might be sizedat 600 cfm to 900 cfm. But there are trade-offs. “You have to have a very significant airvelocity, and when you have significant air ve-locity, other things happen,” says Wolbrink.“I’ve heard stories of steaks that are hot onone side and not as hot on the other.”

Downdraft vents centrally located in thecooktop don’t have to pull contaminants theentire depth of the cooking surface to ventthem (drawing p. 96). They do, however,

have to turn grease, smoke and moisture 180°before they can be vented. Once again, cook-ing style counts for a lot.

Island installations present another prob-lem: crosscurrents of air that can diminishventing efficiency. Wolbrink recalls one homein which a 1200-cfm vent had been installedover a big range in an island. When the hooddidn’t perform adequately, the homeownersadded a second 1200-cfm blower. Even thatcolossal power wasn’t doing the job. Wol-brink was so intrigued he drove out to see theplace. The problem? Leaky windows in anadjacent breakfast room. As the blower speedincreased, so did the unwanted drafts. A vo-luminous 30-in. high hood didn’t help. Butwith the breakfast-room door closed, theproblem disappeared.

In some cases, a high-output cooktopplanned for an island and peninsula mightbetter go against a wall where a large hood isn’t such a visual issue. “Especially if they’regoing to put in one of those 48-in. cooktopswith four burners, a griddle and a grill,” saysHoldsworth. “Now you’re talking aboutputting in a pro-style island hood, and youmight as well put up a wall if you’re goingto do that. Big island hoods are heavy and dif-ficult to mount.”

Filters trap the greaseAll but the large professional-style hoods usealuminum-mesh filters to trap grease (topphoto, facing page). You get what you pay for.Filters on the less-expensive models are flim-sy in comparison to those on more expensiverange hoods. The best ones are reinforced witha stainless-steel plate for additional stiffness.

Aluminum-mesh filters should be cleanedregularly with soap and water, and many of

Chimney-style hoods can work in a wall in-stallation or over an island. This hood’sstainless-steel construction and seamlesscorners make it easy to keep clean. Photocourtesy of Broan-NuTone.

IMPROVING EFF IC IENCY

Manufacturers universallyrecommend that rangehoods be vented to theoutside. Many hoods, in-cluding over-the-range mi-crowave ovens, also can beset up to filter air and recir-culate it back to the kitchen

through aluminum-meshand carbon filters.

Manufacturers offer recir-culating hoods becauseoutside ducting in some sit-uations is virtually impossi-ble. But no one claims thatthey work as well as con-

ventional hoods. “It is whatit is,” says kitchen designerLinda Eberle. “It’s betterthan nothing.”

Recirculating systems usethe same kind of aluminum-mesh filters found in duct-ed hoods to trap grease.

Vents that don’t really vent

Hoods are typically as wide asthe cooking surface. But effi-ciency can be improved by ex-tending the hood 3 in. pastthe edge of the cooking sur-face to create a larger capturearea for kitchen contaminants.

Recirculating devices:

3 in.

them are dishwasher-safe. Don’t wash themwith bleach, however, because it will corrodethe metal.

Instead of mesh filters, high-capacity hoodswith high airflows use stainless-steel baffles

(photo left). Greasecondenses as air isdrawn over the bafflesand collects in a shal-low trough at the backof the hood.

Remote installation maylower noise levels for high-capacity fansBlowers are not asnoisy as they used tobe, but big hoods canmake a racket. Ram-mien says that a fewrange hoods are capa-

ble of operating at 1.5 sones, but most operateat between 3 and 3.5 sones, and the noise frombig ones may climb to 8 sones. Unlike thedecibel scale, sones are a linear value. That is,2 sones are twice as much noise as 1 sone.Wolbrink says that 1 sone is roughly theamount of noise made by a quiet refrigeratorin a quiet kitchen, not noticeable over othereveryday noises and not enough to interferewith conversation.

Installing a blower away from the kitchen(in the duct itself or at the terminal fitting)may lower noise somewhat. “One potentialbenefit is usually the noise factor,” says Ram-mien. “A properly sized and properly installedin-line fan will have a tendency to produceless noise in the living space than the typicalrange-hood setup.” But don’t look for mira-cles. When a blower pulls a lot of air, it stillhas to get through the filters and ducts, andthat can be noisy. Vent hoods typically comewith variable-speed control switches that al-low the blower to be turned up and down. So

one option is to have a big blower that runs atidle until a cooking chore demands a higherblast of air. Some hoods automatically kick upthe blower speed when they sense high heat.One of them is made by Zephyr(www.zephyronline.com; 888-880-8368).

Manufacturers also may recommendswitching to a remote motor installationwhen the homeowner wants to bump up thesize of the blower but can’t squeeze it into thehood. Many models can be set up with eitheran integrated or remote motor.

Fantech (800-747-1762; www.fantech.com)has tackled the noise problem with an in-linesilencer that works like a muffler. Lind-say Ambler, the director of engineering forthe company, says that the silencer reducesnoise levels by 60% to 80% without affectingthe device’s airflow. It’s available in 8-in. and10-in. sizes. �

Scott Gibson is a contributing editor toFine Homebuilding. Photos by JosephKugielsky, except where noted.

Most manufacturers say theycan be washed in a dishwash-er when they get dirty. In ad-dition, recirculating hoods arefitted with carbon filters thatare intended to remove cook-ing odors. Carbon filters mustbe replaced periodically.

Some hoods have an indicatorlight or other type of signal toremind a homeowner tochange the filter. But on manyothers, there’s no easy way totell when carbon filters needreplacement other than to useyour nose. When smoke and

cooking odors seem undimin-ished by the filter, it’stime to replace it.How long a carbonfilter lasts dependson how heavily it hasbeen used.

—S. G.

A high-powered range hood pulls

enough air to empty a 10-ft. by 14-ft.

room in less than 60 seconds. In older

houses, there may be enough leaks in

the building envelope to supply make-

up air. But in newer, tightly constructed

houses, many potential air leaks are

sealed. As a result, a potential hazard is

backdrafting, a condition in which com-

bustion fumes from fuel-burning appli-

ances such as water heaters and fur-

naces are drawn into the house to

replace air that’s being forced out by a

kitchen blower.

Commercial building codes require

makeup air to be provided when venti-

lation equipment is installed. But resi-

dential building codes don’t address

the issue directly, says Chris Holland, a

technical staff member at Building

Officials and Code Administrators

International (BOCA). Holland says a

range hood that exhausts up to

300 cfm and is used intermittently

probably won’t cause problems.

Minnesota appears

to be one of the few

states that require

either passive or

powered makeup air

in new residential

construction to offset

exhaust fans. Exact

requirements depend on the

number and power of exhaust

fans in a house, and whether the fur-

nace and other appliances have sealed

combustion chambers. But the code can

require powered makeup air when ven-

tilation equipment exhausts as little as

175 cfm.

Minneapolis architect Dale Mulfinger

warns clients that providing makeup air

for powerful blowers can be expensive.

A system to offset a 1200-cfm hood

over a big commercial-style range

might cost $500 to $700. “I try to talk

people out of the monster ranges all

the time,” he says.

—S. G.

Aluminum mesh filter

Stainless-steel baffles

Carbon filter

Makeup air: No national standards, but be wary

FALL/WINTER 2002 99