August 22, 2018

Why Range Hoods Don’t Work

To avoid kitchen air pollution, you want a wide, 200-cfm range hood that is installed as close to the burners as possible

This limestone-covered range hood looks pretty — but does it actually work?

Last month at ACI in Baltimore I attended an interesting session about range hoods. It was chock-full of useful information and very well presented (often a hit-or-miss proposition at many conferences).

I was planning on waiting until the slides were available online, but I’m anxious to share this information. I will update this post when I have a link available.

Why we need range hoods

I thought I knew what range hoods do, and I had the basics down, but it was interesting to find out all the nasty stuff that ranges, particularly gas ranges, create when in use. There’s moisture from whatever we are cooking, as well as from the fuel as it burns. I get that carbon monoxide (CO) is produced as the burners start. What I didn’t know about was the nitrogen dioxide (NO2), ultrafine and fine particles, and most surprisingly, formaldehyde, a byproduct of heated oil.

Clogged holes on greasy burners change the air/fuel mixture, leading to incomplete combustion and more CO. Then we get to the oven. More CO is produced as burners cycle on an off in gas ovens. Any food residue on the oven walls turns into tiny particles when heated that are released into the air and breathed in by a home’s occupants. The hotter the oven, the more particles are released. The very high heat of self-cleaning ovens creates even more of these nasty particles.

Using a best functioning rangehood, vented to the outside, helps keep some these nasty things out of our lungs. And staying out of the house when your oven is on self-clean mode is a good move.

The air in homes with gas stoves don’t meet EPA standards for outdoor air quality (yes, I said outdoor) much of the time. About 40% of these homes exceed standards for NO2, 20% for formaldehyde, and 5% for CO. Apparently the EPA thinks it is OK to have poor indoor air quality inside a house, but not outside.

Well-functioning and vented to the outside

OK, so now that we are terrified to even turn on our stoves, what should we do? We still need to eat.

Well, start by using a range hood. The study that this presentation was based on evaluated a variety of range hoods both in homes and in a lab where they could adjust heights and depths, and switch out different hood types. The conclusion was that most of them don’t work very well, and the ones that do work are so big that they are probably back drafting something in the house. (For more information on this problem, see Makeup Air for Range Hoods.)

The things that make a range hood work are a large capture area – the bigger and lower the better – and a minimum of 200 cfm of air flow. Unfortunately, most hoods aren’t deep enough to cover the front of the cook top and most of them are placed higher than they should be so people don’t bang their heads on them. (I’ve done it plenty of times.) And we haven’t even talked about those recalculating hoods that are just noisemakers.

One interesting, but rather obvious, solution is to use the back burners, as that is where the range hoods draw the best. Also, it is a good practice to start the hood before you turn on the burners to exhaust CO.

High-volume hoods should be used at their lowest settings, and if they don’t have a makeup air system (and how many do?) in a tight house, opening a window helps avoid back drafting.

Like many things we learn about how homes work, range hoods seem to not work properly more often than not. If we can convince homeowners to buy (and manufacturers to offer) large, low-volume range hoods, install them low enough to work effectively, and convince homeowners to operate them properly, then we might make some progress on improving the air quality in our kitchens and homes.