More makeup air and exhaust questions for a commercial kitchen

[Sifu]

Can the required outdoor air for a commercial kitchen be supplied by the makeup air unit for the hood? If so, does the makeup air unit need to be sized to meet the requirements of the hood and the outdoor air? (2018 IMC which requires OA for kitchens)

Can the required kitchen exhaust (.7cfm/^ft) be provided by the hood exhaust?

Example: If a hood requires 4400 exhaust cfm, and the kitchen space requires 400 exhaust cfm (based on the .7), then does the hood and the makeup air (from all sources) need to equal (or close) 4800cfm? If the kitchen space requires 200cfm of outdoor air, does the makeup air then need to provide 5000cfm?

Code would require the makeup air to be interlocked with the hood, therefore it would only operate while cooking, likewise the hood would only provide the .7 exhaust when cooking. So in the absence of cooking, if all exhaust and outdoor air were provided by the interlocked cooking system, the kitchen would be left without exhaust and outdoor air.

Sorry, this stuff confuses me a little.

 

[klarenbeek]

There's nothing prohibiting the makeup air from also serving as the required outdoor air. 403.3.1.2 (2018 IMC) actually allows it. I've always allowed required minimum exhaust (the .7 CFM) to be satisfied with the hood exhaust based on the fact that the hoods will be operating pretty much the entire time a commercial kitchen is occupied, other than maybe someone doing some sort of non-food prep work after hours such as a manager doing paperwork. Even if it drops down to standby mode the minimum exhaust is still typically more than satisfied. Kitchen exhaust systems are expensive enough as it is without adding additional cost that really doesn't achieve anything.

From my past (years ago!) fast food experience, the first thing to go on after the lights when coming to work was the grill and fryers so it would be ready to go whenever needed. Same thing with either the griddle or ovens in my church's kitchen (larger church that has a commercial kitchen). If they are on, the hood should be running automatically.

In your scenario I would accept the hood exhausting 4400 CFM with makeup air of 4400 CFM.

 

[Sifu]

Thanks klarenbeek. It's nice to find such a direct and relevant answer with a code citation. Then again, I didn't find it...you did.