Kitchen Cooling and Make-Up Air Load Calculator

A commercial kitchen's cooling load is the sum of four streams: heat conducted and radiated through the building envelope, gain from active staff, the share of cooking equipment heat that reaches the room, and the heat and moisture carried in by unconditioned make-up air. Unlike a dining room or office, the appliances and make-up air dominate, so getting the hood and make-up air right matters more than the floor area. For the whole building around the kitchen, pair this with the commercial load calculator, and work out hood exhaust and make-up airflow separately (the ventilation calculator helps with the airflow arithmetic but is not a kitchen exhaust design).

Use appliance input at the operating design condition rather than all connected nameplate ratings, and establish the room heat fraction from appliance-specific data and the hood arrangement. The default 50% is an example, not a hood capture rule. Radiant gain, capture, exhaust rate and duty differ by appliance.

Appliances: 20 × 3,412 × 0.50 = 34,120 BTU/h. Make-up air: (1.08 × 1,000 × 20 = 21,600) + (0.68 × 1,000 × 30 = 20,400) = 42,000 BTU/h. Room subtotal: 8,000 + 34,120 + 2,400 + 42,000 = 86,520 BTU/h, which is about 7.21 tons. Cooking equipment and make-up air together are about 88% of that total. These defaults are example assumptions, not universal design conditions.

Room loads exclude make-up air and use illustrative envelope gains of 4,000, 6,000, 8,000 and 12,000 BTU/h and staff gains of 1,200, 2,400, 2,400 and 3,600 BTU/h. Make-up air is shown separately, assuming unconditioned air with the default 20 F and 30 grains/lb differences (42 BTU/h per CFM). Add the make-up column to a room column if the make-up air reaches the room unconditioned. These are scenarios, not recommendations.

• Sizing on floor area alone — a per-square-foot rule ignores the appliance and make-up air loads, which can outweigh the envelope and people combined.
• Forgetting make-up air — the outdoor air that replaces hood exhaust carries a large sensible and latent load. Enter only what reaches the room unconditioned.
• Counting make-up air twice — if a separate make-up air unit conditions the air, its load does not also belong on the room air conditioner.
• Applying one hood factor to every appliance — radiant gain, capture and duty differ by appliance, so use appliance-specific data where possible.
• Crediting a hood that is undersized or poorly positioned — if it cannot capture the plume, treat the equipment as effectively un-hooded.
• Entering the full nameplate by default — use operating input after duty and diversity, then justify the number.
• Using residential ventilation to design commercial exhaust — hood exhaust and make-up airflow need a kitchen ventilation specialist.
• Grossly oversizing the AC — an oversized unit short-cycles and leaves the kitchen humid.

Cooking equipment rejects heat to a kitchen in two distinct ways, and a load calculation behaves differently for each. Convective gain is the hot air and combustion products rising off a fryer vat, a griddle plate or an open burner, a buoyant plume that an exhaust hood is purpose-built to catch. Radiant gain is infrared energy streaming off any hot surface (the face of a broiler, an open oven door, a glowing salamander) in straight lines until it strikes the floor, the walls and the bodies of the staff. The ASHRAE Handbook - Fundamentals tabulates heat gain to the space for many appliance types, with and without exhaust hoods, and its appliance-specific values are a better basis than a single fraction.

The split matters because a hood mostly intercepts the convective stream. Even a well-designed Type I hood over a charbroiler does little about the radiant fraction, which is why a good installation still leaves a meaningful share of the appliance input inside the conditioned space. How big that share is depends on the appliance, its surface temperatures and the capture performance, which is exactly why the calculator leaves the room fraction editable instead of fixing it. Idle (standby) heat gain, the load before any food touches the surface, can also be a substantial share of peak, so appliance duty matters when you pick operating kW.

The practical takeaway is that the cooking line and make-up air, not the building shell, set the equipment size. In the casual-diner row above, 25 kW of input releases about 85,300 BTU/h at the appliances; with half of that reaching the room it still exceeds envelope and staff gain together (10,400 BTU/h) by a wide margin. That inversion is why a per-square-foot estimate borrowed from office or retail work tends to undersize kitchens, and why an appliance-driven calculation is worth the effort.

Commercial kitchen ventilation is one of the most heavily regulated parts of a building, and the heat-load math sits inside that framework. NFPA 96, the Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations, governs the construction, clearance and exhaust of Type I hoods, the grease-rated hoods placed over fryers, ranges and broilers. Type II hoods handle heat, steam and condensation (over dishwashers, some ovens and steamers) and carry no grease duty. ASHRAE Standard 154 addresses ventilation of commercial cooking operations, ASHRAE 62.1 sets minimum outdoor air for occupants, and the International Mechanical Code and local amendments govern permitting. Knowing which hood class sits over each appliance is the first step in deciding how much of its heat ever reaches the room.

Every cubic foot per minute a hood exhausts must be replaced by make-up air, and that balance is where many kitchen designs go wrong. If a hood pulls 2,500 CFM and the building supplies only 1,800 CFM, the kitchen runs 700 CFM negative: outdoor air leaks in through doors and gaps, the hood loses capture and combustion appliances can backdraft. Codes generally require make-up air beyond a modest exhaust rate, often through a tempered make-up air unit (MAU) that pre-conditions the incoming stream. Conditioning that outdoor air is a load, and in a humid climate it is frequently the larger of the two big numbers. This calculator lets you include the part that arrives at the room unconditioned, or enter zero differences when a separate unit has already done the work.

Staff comfort is the human reason all of this exists. A line cook works beside radiant surfaces for an entire shift, so the goal is not merely to hold a thermostat setpoint but to keep radiant temperatures and air velocity tolerable at the cooking stations. A balanced hood and make-up air system delivers replacement air low and gently toward the line, rather than dumping cold air that the hood promptly pulls away. When you size whole-building equipment, fold the kitchen result into the commercial load calculator so the rooftop or split system covers the dining room, the kitchen and the tempered make-up air as one coordinated total.

• Type I hood — grease-rated, over fryers, ranges and broilers; governed by NFPA 96, with required fire suppression.
• Type II hood — heat and steam only, over dishwashers, some ovens and steamers; no grease handling.
• Make-up air unit (MAU) — tempers and supplies outdoor air to replace exhaust and keep the kitchen near neutral pressure.
• ASHRAE 154 and 62.1, IMC — kitchen ventilation, occupant outdoor air and the adopted mechanical code requirements.

Have a kitchen ventilation specialist check capture, pressure balance, gains and local requirements before equipment is ordered. This tool is a screening subtotal; it does not design a hood, a make-up air system or a fire-suppression package. ASHRAE Handbook - Fundamentals provides heat-transfer, air-property and appliance heat gain background, and example inputs here are stated scenarios, not prescribed handbook values. For residential design, ACCA Manual J, S and D address load calculation, equipment selection and duct design. This calculator does not certify a complete design or code compliance.