What is make-up air in a commercial kitchen?

The balance problem

Air is bookkeeping: what leaves must arrive. A kitchen exhausting 4,000 CFM with no make-up air pulls the building negative. Doors stand open against closers or whistle at the seals, pilot lights and gas equipment can backdraft, the dining room's conditioned air is consumed as kitchen supply, and the hood itself underperforms — a starved hood spills smoke and grease into the kitchen it was meant to clear. The building does not negotiate; an unbalanced system finds its air through every leak in the envelope and charges the HVAC system for conditioning it on the way through.

The ways make-up air is supplied

Dedicated make-up air units deliver tempered outdoor air directly to the kitchen, usually discharged through the hood's perforated supply plenum or nearby diffusers arranged not to disturb the hood's capture zone. Transfer air from the dining area is the second source — deliberately sized openings let conditioned dining air replace part of the exhaust, which recovers its conditioning value. Most real designs blend the two: transfer air up to the point the dining system can spare it, dedicated supply for the balance. Untempered make-up air is permitted in some climates and code editions within limits, and it is exactly as uncomfortable as it sounds in a Phoenix summer or a Minnesota winter.

Tempering, controls, and the interlocks

Dedicated make-up air is usually heated, and in hot climates increasingly cooled, to keep the kitchen workable — an unconditioned 120-degree supply stream over a cooking line is a staff-retention problem. The make-up unit is interlocked with the exhaust: it runs when the hood runs, and its volume tracks the exhaust rate where the hood system modulates. These interlocks, plus the fire-suppression and shunt-trip relationships on the cooking equipment, live on both the mechanical and electrical sets. When the two sets are drawn by different hands at different times, the interlocks are where they disagree — and the disagreement is found by the inspector, not the designers.

What Torch delivers

Torch designs the hood exhaust and the make-up air as one system on one set: exhaust rate from the equipment and hood geometry, the transfer-versus-dedicated split calculated against the dining HVAC, tempering sized for the climate, and the interlock sequence stated identically on the mechanical and electrical drawings. The balance is shown in the ventilation calculation the jurisdiction reviews, so plan check sees the whole bookkeeping, not just the exhaust half. Send the equipment list and the floor plan; the hood and its air are scoped together, as they should be.

The bottom line

Make-up air is the supply half of the hood system: balanced, tempered, and interlocked with the exhaust. Design it deliberately or the building supplies it accidentally — through the dining room, at HVAC prices.

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