foodservicenerd
Calculators & tools

Make-Up Air (MUA) Calculator

Estimate the make-up air your kitchen needs to balance a Type I exhaust hood — enter the hood’s exhaust CFM and your make-up ratio.
Planning estimate — a licensed mechanical engineer sizes and balances the real system per the IMC and your local authority.
kitchen cook line Exhaust 100% Make-up air ~85% remainder = transfer air from the dining room / HVAC
The hood exhausts air; make-up air (often ~80–90% of exhaust) replaces most of it, with the rest as transfer air — keeping the kitchen slightly negative so odors stay out of the dining room.
2,550 CFMdedicated make-up air at 85% of exhaust

How it works

A Type I hood exhausts grease-laden air; that air has to be replaced or the building goes negative and the hood stops capturing properly. Most of the replacement is dedicated make-up air (often ~80–90% of exhaust); the rest comes from transfer air (air migrating from the dining room / HVAC). Keeping the kitchen slightly negative relative to the dining room keeps odors out of the front of house.

First size your exhaust with the hood CFM calculator, confirm you even need a Type I hood with do I need a hood?, and read ventilation & make-up air explained.

Frequently asked

What is make-up air?
Make-up air (MUA) is tempered outdoor air brought into the kitchen to replace what the exhaust hood removes. Without it the space goes negative, the hood can't capture smoke, doors are hard to open, and other appliances can backdraft.
How much make-up air do I need?
Codes generally require replacing most of the exhausted air — commonly about 80-90% of the hood's exhaust CFM as dedicated make-up air, with the balance coming from building transfer air or HVAC. A mechanical engineer sets the exact split for a balanced building.
Is make-up air the same as exhaust CFM?
No. Exhaust CFM is what the hood pulls out; make-up air is what you bring back in. They're closely matched but not identical — you typically supply slightly less than you exhaust so the kitchen stays gently negative relative to the dining room.
Does make-up air need to be heated?
In cold climates, yes — dumping raw winter air on the line is miserable and can trip appliances, so MUA units often temper (heat, and sometimes cool) the incoming air. That tempering is a real cost line in the mechanical budget.