1200 CFM hood makeup air?

[jud aley]

I’ve read Martin Holidays article on Kitchen Hood makeup air and was wondering if anyone has firsthand experience with one setup or another?

Our HVAC sub wants to run the makeup air directly into the hood. I’m skeptical that this will “short circuit” things and will not draw out much of the cooking fumes from the stove top.

The owners bought a 1200 cfm hood because they want to get as much of the cooking odors out of the house as possible.

I’m of the opinion that the makeup air supply should be fed into the HVAC return at the farthest point away from the kitchen. My thinking is that if the exhaust hood is turned on and the HVAC system is not calling for heat/AC the makeup air will be pulled back wards out the closest return register, flow thru the house and be “tempered” as it moves toward the kitchen. If the temperature changes too much inside the house because the introduction of the makeup air the thermostats will trigger the system and the makeup air flow will be reversed and start to flow the correct way thru the return into the air handler and be mixed with the heated or cooled air as it flows toward all the supplies in the house.

[James Eggert]

I guess in theory your way works! In my own ICF home I use an 800-1000 cfm exhaust, don't remember now. But I also used similar arrangements in clients' homes. The object of tempering air assumes you will be running the exhaust for a very very long time, which typically is not the way a kitchen exhaust works. I would say 30-40 minutes MAX.

In the past I brought either a 4" or 6" d line from outside, could even be from the attic, to a grill in the ceiling right in front of the hood. If you set it up with a Cape backdraft damper it only brings in air when the exhaust fan is on. Being on the ceiling it is drawn into the hood, and doesn't even ruffle the cook's hair!

I learned about residential make-up air the hard way. I do not have make-up air in my house; turn on the fan and the door to the deck is pulled open if it's not latched tight. I always made the make-up air duct for my clients!!

[ThingOfBeauty]

We've been dropping them into HVAC systems, on the same sort of theory that it will be more tempered and more diffuse and less obvious than dumping directly into a room.
We usually put it into a return pretty close to the air handler.
One of our HVAC guys likes to force the system fan to run whenever the damper is open, the other two don't. I lean toward not tying it in and letting the clients decide to kick on the fan if desired/needed.
For big range hoods, we're putting in 8, 10, or 12 inch duct and dampers.

[jud aley]

A couple of things I should add.

There is a dryer in the room next to the kitchen and the door between them will be open most of the time.

There is a fireplace in the living room and an oil fired furnace and water heater in the basement both of which are atmospherically vented.

I don’t want to pull a draft down the chimney and/or start pulling the smoke out of the flue pipe if there was to be a call for heat while the hood is running.

We are planning to weather strip the door to the basement and add a sweep to try and isolate the furnace and water heater from the draw of the hood.


Not sure how either of these two makeup air systems would respond to these items or if one is better than the other when it comes to dealing with the furnace, water heater and fireplace.

[steve demetrick]

Jud,
One big factor playing into this is how tight the house is. If it's a very leaky house to begin with, you might not have any issues to worry about. If it's a pretty tight house (3ACH or less), there should be balanced makeup air for the range hood and the combustible appliances in the basement, and I would consider putting sealed glass doors on the fireplace as well (opened only when using the fireplace. Might be worth having the house tested with a blower door so you can get a handle on what you're up against. With all those parts wanting to suck air out of the house you could be setting up a battle royale.

-Steve