When planning for a new kitchen or when purchasing a new kitchen appliance, it is important to plan ahead and make sure that everything is working effectively and safely. One aspect that is important to safe kitchen operations is an effective exhaust system.
However, an effective enough exhaust system can cause its own set of problems, which is where makeup air comes into play. Let’s look into if makeup air is necessary for a domestic kitchen and how to install a properly working makeup air unit.
Domestic kitchens can require makeup air units if they meet certain requirements. The kitchen must contain a fuel-burning appliance, use an exhaust system, and the exhaust system must have a rate of 400 CFM or higher. Some kitchens that don’t meet these criteria will benefit from makeup air.
When Domestic Kitchens Require Makeup Air (IRC)
Section M1503 of the IRC covers domestic cooking exhaust equipment. It specifies “domestic”. Section M1503.6 details makeup air, specifically.
Makeup air is required if:
- The kitchen must contain a fuel-burning appliance.
- This appliance must use an exhaust system (it is not direct-vented or uses a mechanical draft venting system).
- The exhaust system must be one that exhausts more than 400 cubic feet per minute (CFM).
For the first requirement, your kitchen is likely to have one or multiple fuel-burning appliances, such as your stove, oven, or range.
When it comes to fuel-burning appliances, they need to consume oxygen to run properly, and then the byproduct gasses from the fuel-burning appliances are then exhausted from the home.
Without makeup air, the loss causes depressurization in the home. This depressurization can then lead to backdrafting, where combustion gasses can reenter the home.
If your fuel-burning appliance uses a direct vent or mechanical draft venting system, then you do not need to worry about having a makeup air system.
This is because these systems use air from outside your home, meaning that they won’t cause depressurization.
However, it is important that, when your exhaust system exhausts more than 400 CFM and uses air from your home, you have a makeup air unit. This is because, above 400 CFM, you are at risk of depressurization.
Make-up Air Requirements
If your kitchen requires a makeup air unit, then you need to make sure that it is working properly and has the proper setup.
The first requirement is that the makeup air unit must provide as much air as is being exhausted. This is required because, if the unit provided less, then depressurization would still occur as more air is lost than is being added.
The type of unit you get is up to personal preference.
One type of unit introduces makeup air passively. This is when makeup air is naturally drawn into a room because of the depressurization.
On the other hand, you can also get a unit that introduces air mechanically, using a motor-powered fan to pull air into the system.
The unit must also introduce air into the same room in which the exhaust system is located.
A possible alternative to this would be to introduce air into a room or duct that is in permanent and direction connection with the room containing the exhaust system. The IRC does add:
“Such permanent openings shall have a net cross-sectional area not less than the required area of the makeup air supply openings.”IRC M103.6.1
Finally, it is required that your makeup air unit has a damper. This is to keep the pressure in your home balanced. The damper only opens when the makeup air is required.
If it was permanently open, then air would be able to enter and leave without control. Conditioned air would escape or cold/hot outside air would enter, making your HVAC work harder.
When adding a damper to your makeup air unit, be sure also to follow the requirements laid out for dampers to allow for safe and effective use of the unit.
For one, the damper must be a gravity or electrically-operated damper. This means that it, in one way or another, automatically opens when the exhaust system is on.
This is important because, if it does not open automatically, then makeup air is not able to enter the room when it is needed.
If this happens, then the unit is basically useless. That is why it is important that the damper is able to operate automatically in conjunction with the exhaust system.
Another requirement is that the damper must be accessible. This is important because, by having it accessible, proper maintenance is able to be performed to keep it working effectively.
If you are planning to use a gravity or barometric (pressure-controlled) damper, your makeup air unit cannot introduce air passively unless it is designed to operate with a pressure differential of 3 Pa or less.
What this means is that your unit must be able to provide makeup air when the pressure in the room decreases by 3 Pa or less if it both introduced air passively and has a gravity damper.
This requirement is in place to ensure that the system is able to provide the necessary air to prevent backdrafting.
Common CFM Size of Domestic Kitchen Exhausts
Common CFM sizes for kitchen exhaust systems range greatly and are based on a variety of different factors.
One important factor is the type of appliance that is being exhausted.
Electric appliances, such as electric stoves, are going to need a much lower CFM than gas stoves and ranges because you are only exhausting the cooking byproducts, not combustion byproducts as well.
So, you can typically expect that electric appliances are going to have CFM ranges below 400.
Another factor is the size of the stove or range. The larger the stove, the more CFM it is going to require to exhaust properly. Therefore, a large range, such as ones that are commercial models, is likely to have CFM ranges above 400 and would, therefore, require a makeup air unit.
Finally, the power of your stovetop can also influence CFM ranges. Burners that have an output of over 35,000 BTUs are going to require much stronger exhaust systems than burners that output less. This also means that powerful burners are also going to require a makeup air unit.