Selecting A Kitchen Exhaust Fan

HOME CLINIC: We plan to remodel the kitchen and are thinking about new appliances and where to put them. My husband and I disagree about whether to put in a kitchen fan. Even if we do, we both have misgivings about how they look and how noisy they are. What do you suggest? - K.B., Seattle

DEAR K.B.: First off, we think a kitchen exhaust fan is an essential part of a modern kitchen. It can do wonders for getting rid of odors and excess moisture. There are three things, besides cost, you will want to consider: where to put it, how it looks, and how noisy it is.

Where you put it not only affects how it looks, but, more important, how effective it is. In part this will depend on the type of cooking you do. The quality of the fan and the duct work will have a significant effect on the noise it makes. The noise level, in turn, determines whether you use and benefit from the fan.

For the most effective fan, our recommendation is to find the quietest wall-mounted hood that covers a large portion of the stove surface, then install it properly. If you are really tied to the downdraft style of fan, we suggest you get the rear-mounted, pop-up type and alter your cooking style to put the tall pots on the rear burner.

If you can, get a variable-speed control. It will often allow you to adjust the annoying noise level so you continue to use the fan. While you want whatever you choose to fit the look of your new kitchen, you also want it to be convenient, pleasant to use and effective.

We have learned much about kitchen fans from Wanda Olsen, an associate professor and housing-technology specialist at the University of Minnesota. She has researched the performance of this equipment and written a very informative article on it in the August 1991 issue of The Journal of Light Construction. Here's a brief summary of her main points.

Hoods vs. Downdrafts

Most people are familiar with hooded fans mounted above the stove with a canopy to collect moisture, odors and combustion gases. These are more successful at removing the contaminants from cooking than downdraft fans are - mainly because those products rise off the stove top.

A downdraft fan, mounted in the stove top or at the rear, has to pull against this natural tendency. Surface-mounted downdraft fans are successful with gases, grease and moisture from the grill unit or pots less than 3 inches high, but don't work so well with taller ones.

The pop-up, rear-mounted downdraft fans are more successful with tall pots because the vent rises to about 8 inches. Even then, that success is limited pretty much to the rear burners. Downdrafts are also more open to the room, so they tend to move a lot more air that doesn't contain the contaminants you are trying to get rid of.

Hooded exhaust fans are not automatically perfect either. The size and location of the canopy are critical for good capture of contaminants. The most successful will have a canopy at least 20 inches deep (measured front to back) and no more than 20-24 inches off the stove top. If you (or other members of your household) are tall, you may find this height annoying. Many hoods are only 17 inches deep. The larger the portion of the surface the hood covers, the more effective it will be.

You didn't mention whether your stove is against the wall or on an island. Of the three or four types, the wall-mounted units seem most effective. Island hoods often work well when they are large enough to cover most of the surface, and powerful. One drawback is that they are usually mounted about 27 inches above the surface to maintain sight lines. This reduces effectiveness.

Other types of hoods

More recently two other types of hoods have shown up - microwave/hood combinations and slim line or "silhouette" fans. The microwave/hood combination is convenient, but less effective than a conventional hood because it doesn't project out as far and doesn't have much of a collecting canopy, if any. They work well for the back burners, but are not very effective for the front ones. Olsen thinks you are better off installing a conventional hood and putting the microwave elsewhere.

"Slim line" or "silhouette" fans are the sleek units that pull out over the stove under a cabinet. Stylish, but rather flat in terms of canopy. They were not included in any of Olsen's testing, but she expects them to be somewhat more effective than the microwave combination units.

Power AND noise

We generally recommend the fan be able to remove at least 100 cubic feet of air per minute (cfm) when it is installed. Olsen recommends more - from 150-200 cfm for all mounted hoods. The other types require higher air flows in order to capture the pollutants.

It's common to find downdraft fans and island hoods in the 500-600 cfm range. From an energy-use point of view, this is a disadvantage because they exhaust a lot of air that does not contain contaminants from cooking, but is heated by your furnace. The higher flow rate is likely to mean a louder fan as well.

Fans are rated for noise by sone levels; the higher the number the louder the fan. A 2-sone fan seems twice as loud as a 1-sone fan. While there are a few range fans in the 2.5-3 sone range, most are between 4-7 sones, and still others hit 9. This is a practical consideration; most people will find 4-7 sones irritating. Go higher than that and they just won't use the fan. Even with a 4-7 sone fan, it can be difficult to hold a normal conversation when the fan is running.

The type of fan will make a difference in how much noise it makes and how much air it moves. We recommend you look for a centrifugal blower (squirrel-cage) rather than a prop-style axial fan (propeller). Most quality units will use a squirrel-cage fan to overcome the duct-work resistance. Keeping duct work short, smooth and large will help the fan operate more easily and quietly. At least, follow the manufacturer's recommendations.

Produced by the Energy Extension Service, a division of the Washington State Energy Office. If you require special assistance or auxiliary aids, please contact the Washington State Energy Office at 1-800-962-9731.