Make Up Air
malba2366
| Posted in General Questions on
We are redoing our kitchen and the local inspector is requiring active make up air. Is there any downside to installing an unheated system and having that blow into the second story foyer adjacent to the kitchen? I have been given options for a heated and unheated system but I think it would be much more cost effective to let my gas furnace turn on than to use a 10,000 watt resistance heater in the makeup air system. Dumping the cold air into the HVAC return is not an option because my HVAC system uses a proprietary communication system and the make up air system can not turn on the furnace fan.
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The makeup air can go into many places, foyer is fine as long as it is open to the kitchen. A good spot is behind the range or high vents above the stove. The MUA also does not have to kick in when on low speed, so in most cases it won't operate so you don't have to worry about cold draft.
If not yet installed, might be worth to revisit your hood choice. A good hood (something with wide opening and large capture volume) doesn't need a big blower to be efficient. A 400CFM is would be fine for most which gets you out of MUA requirement.
If the stove is gas, the make-up air requirements are more stringent than electric or induction, so another option would be to consider swapping to an electric cooktop! As part of "redoing our kitchen" that might be a relatively easy move. Easier now than when the place is done.
This is only true if there are no other combustion appliances in the house.
I can't get the MUA into the kitchen without tearing up a lot of the house. Basement is finished. The only place I can get it to easily get it to is the foyer through the attic - this area communicates to the kitchen with no doors in between. We do need the hood for the cooking style we use, and the gas/induction thing is not really negotiable to maintain sanity in the house if you know what I mean...
Is it ok to vent the cold air into the house, I live in NY so gets below freezing in the winter. It is far enough away from the kitchen/living rooms that it will mix with air in the house and kick the furnace on. I am just concerned that there will be an issue with the cold, dry air hitting the humid air in the house.
The hallway location should work. Besides cooling the hallway, there won't be issues with the MUA there and since it is connected to the kitchen area it will still work. Outside air is cold but it is also dry, so it won't cause condensation issues. Make sure the MUA damper is positive sealing with a gasketed damper. A filter box in the attic would also be a good idea.
As for gas VS induction. I had cooktop that had both induction and gas burners for a long time. My wife for a time refused to use the induction side as it wasn't "hot" and would not make the food "crispy" enough. Slowly, tried the induction and eventually stopped using the gas side completely. Induction was simply faster, hotter, better control, and no issues with burnt fingers on pot handles and ladles.
Eventually I managed to crack to cooktop surface and the replacement is now all induction. Ditching the gas burners was fully approved by management.
You only need makeup air if you have combustion appliances in the house. The purpose of makeup air is to prevent combustion from backdrafting.
My advice would be to install an induction cooktop and see how you like it without makeup air. You can add makeup air later if you're unhappy with it.
This only works if the house is all-electric.
House does not need to be all-electric to omit the MUA. Fuel fired appliances that are forced induction like condensing tankless water heater, high-efficiency furnace are also fine. At least that is how my local code reads.
True.
The point is that the code requirement for make-up air isn't because the vent fan somehow won't work well without it, it's to keep the combustion appliances from backdrafting. Which forced draft does as well.
My experience is that even in a relatively tight house vent fans can work perfectly well without make-up air.
Section 505.4 of the 2021 IMC requires that domestic kitchen exhaust hoods are provided with makeup air if their exhaust rates exceed 400cfm. I think this may be where the code official is coming from.
I'm assuming you have already installed your hood vent but if not have you thought about a compensating hood vent? It both supplies and exhausts air at the same time.
This has come up before here, feels like a good idea but it doesn't work. It is a good option if you don't actually cook and need a proper working hood.
Those types of hood do comply with code but they don't work as a hood. The issue is the makeup air is carried away by the exhaust fan right away which reduces the amount of effluent it can suck up.
They are very good way of turning a 1000CFM hood into a 200CFM one. Since there is a lot of airflow right by the hood, it also adds turbulence which increases the amount of spill from the stove.
If you look at commercial kitchen guidelines, they limit the amount of make in in the hood to max of 20% of the total for this reason. Think about it this way, you want the makeup air to approach the stove at very low speed evenly from every direction. This helps contain the thermal plume which rises into the hood where the exhaust fan discharges it outside. This is the reason you also want a hood with good capture volume.
Bonus is since the makeup air is exhausted right away, it won't cool the house :)