Make up air
Asuming a new construction (4800 sq ft), where the walls are sealed and insulated and all the appliances are direct vent.There is a kitchen hood providing 6oo cfm and a dryer providing about 200 cfm.Also, an ERV providing about 200 cfm .Would a make up air still be beneficial to prevent the depressurization of the house if the electric dryer and kitchen hood run in the same time?I know that if all appliances are direct vent then most codes do not require make up air (I am not talking about combustion air which is a different animal) .But still, depressurizing a house is still not a good idea, as far as resident comfort is ,even if it may be permitted by code,right?
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Replies
AL2023,
You don't say where you are building, but most codes require make-up air for any range hood over 400cfm.
Only if you have combustion appliances in the house.
It's bad to depressurize your house for other reasons. Doing so can draw radon into the living space, draw stormwater in through cracks and gaps (I used to have a video showing that happening at a window on a project of mine), reduces the efficacy of the exhaust appliances to the point where they may hardly do anything, and it can even make it hard to open or close exterior doors. Balanced or slightly positive pressure in the house is much better, even if you don't have combustion appliances. If you do have combustion appliances, it's critically important to avoid negative pressure.
What is the average ceiling height? What air tightness ACH50 are you shooting for? Calculate the leakage at 50 Pa and see if it is more or less than the 800 CFM (which is 48,000 ft^3/hr). You should really install make up air at those exhaust rates for a well built (< 1 Ach50) house. Especially with some combustion appliances (even if they're direct-vent), this is a no brainer.
EnergyStar requires pressure differentials between rooms to be within 3 Pascals. See Energy Star Checklist section 6.2 here:
https://www.energystar.gov/sites/default/files/asset/document/Rater%20F%20v107%202019-10-28_MU.pdf