Worrying About Kitchen Fans Is Exhausting

One of the things that has always amused and surprised me is the way people will spend a great deal of money to build a green home, with lots of insulation and nontoxic materials, and then put in a big open kitchen with a six-burner semi-professional gas range, often on an island with an exhaust hood four feet above it, like in the Wolf ads reproduced here. These exhaust hoods do next to nothing unless they're close or unless they're designed to move enough air to actually collect what's coming off the stove.

A few years ago on TreeHugger, I described kitchen exhausts as "The most screwed-up, badly designed, inappropriately used appliance in your home." In it, engineer Robert Bean described what happens when people go out and buy a big hood without taking into account how to replace the air being sucked out:

In my opinion the potential health and building problems created by hood induced negative building pressures should rest squarely on the appliance manufacturers and their dealer’s shoulders. The HVAC industry needs to step up and tell these range hood vendors that when you continuously suck way more than you blow, you’re going to create problems for the occupants and the building - full stop.

Then, Bean was complaining about the hoods. In a new article just published in HPAC, a heating and cooling journal, he talks about the whole picture, including what's going into the air while you're cooking. The article is painful to read; Robert fills it with every food pun he can come up with — and I admit I couldn't resist tossing out some puns in the headlines — but he's perhaps a better engineer than standup comic. He outlines the problem, that he says most designers think of as routine as poutine, but in fact, it's much more complex.

It turns out (again) that the things we do on autopilot in our homes are coming back to bite us in the rump roast. It is now apparent to researchers that the smorgasbord of pollutants we sense as aromas, heat and moisture from indoor cooking are reaching concentration levels, which if measured outdoors would have environmental protection agencies shutting down kitchens and issuing fines.

He then lists the chemicals that are the natural byproducts of cooking food in your kitchen:

Since there are no environmental protection regulations governing indoor residential kitchens, your lungs, skin and digestive systems have become the de facto filter for a soufflé of carbon monoxide, nitrogen dioxide, formaldehydes, volatile organic compounds, polycyclic aromatic hydrocarbons, fine and ultra fine particles and other pollutants associated with meal preparation. Toss in the exposed interior design features and what is left behind is an accumulation of contaminants in the form of chemical films, soot and odours on surfaces, similar in affect to what one finds in the homes of smokers.

He notes that this is not a problem from a single meal, but a cumulative exposure to chemicals that are known to have harmful effects, particularly with women and children. The problem is, nobody really thinks about it. Your average kitchen exhaust is chosen with the help of an appliance dealer, not an engineer. There are vague standards in building codes, but in fact it varies according to the home’s size, ventilation system and leakage; and according to culture and food choices. (There’s a big difference between stir-frying a chicken and boiling an egg.)

I was surprised to see these cultural differences in play when I was in China. The open kitchen design is all the rage there like it is in North America, but their stir-fry style of cooking creates a huge amount of airborne smells and oils in a very short time. So many times I saw perfect western modern open kitchens enclosed in floor-to-ceiling plate glass walls, separating the ventilation of the entire kitchen from the rest of the apartment. This makes a lot of sense.

As for some rules of thumb, Robert recommends that the hood be wider than the stove by a few inches on each side (something I have rarely seen) and should be as close as possible, but if it's more than 30 inches away, you need a bigger fan. He dislikes the standard integrated fan and hood that most of us have to keep the noise down; he wants the air to move fast to keep the heavy stuff from settling, and wants the runs straight.

Then there's the big problematic question of make-up air. You're pumping a lot of air out with that exhaust; what's going to replace it? It used to be much easier in leaky old houses because the air just came in everywhere. I won’t go into the complexities but basically, if you're doing anything bigger than a standard range, take it all into account and hire an engineer. What that engineer tells you will scare you, as Robert noted in the earlier post:

Putting this into perspective - with that amount of output you could heat a floor space over 10 times that of the kitchen it is serving. If you did the same exercise but for summer time sensible and latent cooling, you would likely find a similar load for dehumidification of incoming outdoor air.

A few years ago, I thought nothing of having a gas stove in my kitchen, but I've since learned that we are probably better off not having all of those products of combustion inside our house — any more than we would run a propane barbecue there; it's the same stuff. I never even thought about what was coming off the food.

This is all exhausting; it reminds me of the old joke, "What are you making for dinner? Reservations!" I feel like letting someone else worry about it.