Hyperventilation About Kitchen Ventilation

After writing the post "Worrying about kitchen fans is exhausting," where I talked about how important kitchen exhaust was, I got a comment from a reader who said that recirculating fans were OK if they were combined with a proper ventilation system. For me, this was heresy; I have always been totally dismissive of recirculating hoods, considering them little more than noisemakers, or as one expert, Brett Singer, put it, "forehead greasers."

So I sent a question around to a few experts I know to get their opinions, and I have never seen so much hyperventilation on a subject where it is clear that there is no consensus. Engineer Robert Bean of Healthy Heating kind of agreed with me and noted, "I believe it would be difficult to find design professional consensus suggesting comfortability with recirculated hoods without good evidence."

Then I got a note from Elrond Burrell, an architect in the U.K. who told me, "For domestic Passivhaus kitchens, we are using recirculation cooker hoods to scrub the grease, etc. from the cooking air. We want the heat from the cooking to be retained but we don't want the cooking grease to mess up the ventilation system." One U.K. guide to ventilation for houses designed to Passive House standards says, "In kitchens recirculating cooker hoods are recommended to be separated from the MVHR (mechanical ventilation and heat recovery) system. This is to avoid the excessive build up of oil particulates inside the MVHR system and the extract valves should ideally be at least 2 meters away from the cooker."

In fact, the rules are different everywhere. In Ireland, one is allowed to connect the kitchen exhaust to a heat recovery ventilator; in Canada, this is illegal. In California, Passive House builder Bronwyn Barry of One Sky Homes describes what they do:

At One Sky Homes, we've insisted on direct-vent hoods with an in-line damper for makeup air that is delivered either directly above the hood, or in the toe-kick below the cooktop. As Elrond mentioned, the loss of heat is minuscule given the amount of excess heat being generated by the act of cooking at the time the hood is activated. (We switch them on the same circuit so our clients don't have to bother either opening a window or turning on the makeup air fan.)... That said, we can get away with our direct vent & makeup air design because we live in temperate California. Our makeup air isn’t coming in at -20deg!

Consultant John Straube notes that much depends on how much and what you cook:

There is a fair bit of experiential evidence that recirculating fan hoods do not remove enough of the pollutants. This was first taught to me by a property manager for a larger low-income housing development in the 90s who had lots of low cost units with recirc units. Unit owners usually did not clean the filters often enough or well enough because they require too much. Also, many of the contaminants other than coarse grease particles don't get captured — all kinds of gases and particles are released that cannot or are not effectively be captured by grease filters.

But the standard kitchen exhaust fan is not going to break the energy bank. Straube continues:

I mean really, running a range hood at 300 actual CFM for 30 minutes a day is simply NOT an energy penalty....That said, people who install 1200 CFM range hoods also get what they deserve: there is little to require this, and if it is required (commercial kitchen) we should have makeup air.

So in the end, what we have is a really interesting problem. Passive houses and other modern, energy-efficient houses are tested to ensure that they don't leak and that ventilation is controlled, but running an exhaust fan really messes up the math, pumping all of that air out, so they try and get by with a recirculating hood that probably doesn't do the job. If you are not in temperate California and you stick a makeup air unit on there to heat up the incoming air, you are screwing up the energy load calculations; as Robert Bean pointed out, it could be as much energy as is needed to heat the whole house.

It's frustrating. It seems that there really is no clear answer, that more research is needed, it's complicated and confusing. But then I'm just venting.

But it seems clear that all of those beautiful photographs of the big commercial ranges in big open kitchens with exhaust hoods hanging from the ceiling are selling a big lie. Those stoves need a big exhaust fan that is professionally engineered for the size of the stove, and they need conditioned makeup air. What we have instead is a fantasy, the big commercial stove not far away from the Steinway grand which will have furry greasy hairs on all of its strings if that stove was actually used the way it was designed to be used.

I am beginning to think that those Chinese designers are really on to something. If you are serious about cooking and want a big range, and care at all about energy efficiency or health, then you should probably have a separate kitchen with doors and its own properly designed ventilation system.

But if you don't want to go that far, if you want a big commercial style range in your kitchen:

• Hire an engineer who knows something about the subject.
• Put your range on a wall, not an island, where the hood can actually work.
• Think about how much you really cook and whether you really need this big expensive stove that may look great but is going to fill your house with all kinds of stuff you would rather not be breathing.
• Forget about gas and get an electric induction range. You wouldn't run your barbecue inside, but that's essentially what you are doing with a gas range.

And on that note, I am going out for dinner to where they have proper ventilation, fire suppression and a big hot commercial stove.