Elephant in the room (kitchen, in this case)
Mechanical air exchange is rightfully part of every plan in energy-efficient buildings. A lot of effort and no small expense is devoted to choices of HRV or ERV balanced air. The house I am building is 3 bdrm. & 2,000 sq.ft., thus: ((2,000 sq. ft /100) x 3) + (4 x 7.5) = 90 CFM. And this is intermittent, i.e. not necessary during shoulder season months when windows are open (six months here in zone 4A), or during other months when the occupants are working all day or traveling for business. Installing such a balanced system may take 20 years to overcome the cost of simply conditioning outside air that comes through a supply hole in the wall (which would of course come through an MERV 13 filter…)
Okay, most readers will likely advocate for the investment, and I will not argue the legitimacy of their choice. I remain dismayed however that there is no similar discussion about options for makeup air for the dryer (about 200 CFM per load) or the range hood (250–1,500 CFM). Depending on the family, these could equal the ventilation load, and because they come all at once, they may have a larger impact on comfort. And the cooking stuff not adequately ventilated is likely more harmful than stale air. Martin, your last article on the subject was published in 2010; comments date to 2016 but are mostly, “What if I do this…?”
So can anyone tell me how to provide makeup air in an efficient home? I am opting to widen the range hood to 36” over a 30” induction cooktop for a fuller capture. Vent-a-Hood says their 250 CFM is equivalent to 360 CFM because air is moved more efficiently with their squirrel cage design. Choosing induction over gas should make this adequate.
The best “What if I do this…?” so far seems to be to bring in outside air through a pipe that has a flapper with a controller tied to the range hood exhaust (ccbinnovations.com RMAS06 or similar). Several suggest dumping it into the toe kick in front of the stove. Others have put registers on the counter on either side of the stove! Matt Risenger put the range on a platform that acted as a plenum, allowing air to escape up the front and back of the range (https://www.youtube.com/watch?v=NsSvMB9bJeE).
Q1: What is best practice today?
Q2: Would it be less effective if I simply dump the air into the central stairwell, allowing the large volume to act as a mixing plenum?
Q3: If I go with some version of a plenum below the stove—given that it is simply exterior air—do I need to wrap the plenum with metal? Could I not simply build an airtight box our of rigid foam?
Thanks for any help!
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Replies
For the dryer, why not go ventless heat pump?
I've got nothing for you for the range hood though. At present our make up air is just drawn through the present dryer (which is being replaced with ventless next weekend) and the HRV if it's operating. Our range hood is a recirc type.
David,
You are overthinking this. The makeup air can come into the house almost anywhere, through a wall register or a ceiling diffuser, as long as there aren't any closed doors between the register and the kitchen.
Ideally, the duct that conveys makeup air to this register should be controlled by a motorized damper that interlocks with the range hood fan.
Couldn't make-up air for a range hood or dryer be most easily supplied by a small operable window, duct or opening with an insulated cover you opened when running the appliance, rather than a motorized damper? (Says the guy who still likes the crank windows on his pickup truck).
2015 IRC M1503.4 Makeup Air Required – All exhaust hood systems capable of exhausting in excess of 400 cubic feet per minute shall be mechanically or naturally provided with makeup air at a rate approximately equal to the exhaust air rate. Any stove/range that requires an exhaust system of over 400 cfm is required to have a make-up air unit of same cfm. The make-up air is independent from the house make-up air and shall be supplied in same room where the exhaust room is located.
HRVs and ERVs are balanced ventilation systems for your house, not to be confused or replaced with or for the kitchen exhaust ventilation. If you want balanced ventilation with easy and economical systems, you could look into a spot ERV from Panasonic WisperGreen with 50-80-110 or 110-130-150 CFM units.
You could also choose supply only ventilation, which requires to run a ducted outdoor supply air from the outside to the plenum of an air handler, so the air can be mixed with the existing house air. It’s not as good of a balanced ventilation system, but far better than an exhaust only system, which I never recommend.
Sometimes circumstances dictate choice. I'm not sure that I fully understand balanced systems (my house is off-grid in a cold climate and an HRV or ERV requires too much power to run) but it seems to me that balanced ventilation is only balanced at the point that it is commissioned. After that it is subject to the same problems with wind, depressurization etc. that any other house would have. The balanced system simply takes care of the known ventilation load but the rest is still wide open.
I use an exhaust only system and recently had problems with backdrafting on a wood stove when a 40 cfm bathroom fan was running. I had to add a proximity type air duct (which of course is another whole discussion that belongs on another thread) but relevant to this thread: I used a 4" dust collector gate to adjust/control the airflow in. Metal or plastic gates are readily available in a variety of diameters,they are cheap and they work really well. If you want to get fancy there are also automated gates available but you could easily automate them yourself.
There is a more recent article by Martin on makeup air, ie, "How to Provide Makeup Air for Range Hoods", 8 June 2016. In the comment train for that article there is a reference to a Building Science document BSI-070 that also has fairly explicit suggestions and drawings on the topic in the latter half of the article.
Andrew,
Thanks for your comments. My article, "How to Provide Makeup Air for Range Hoods," was actually published in 2010, not 2016.
Thanks for pointing out the Building Science Corporation document from 2014 ("First Deal with the Manure and Then Don't Suck"). I have edited my 2010 article to include a link to the BSC document.
Martin,
Thanks for the correction, not sure how I mixed up the dates.