Room Cooling Heat Load Calculator

The default here is 20 BTU per hour per square foot, a common industry rule of thumb for a typical room with average ceilings and insulation. You can change the BTU per sq ft field for a poorly insulated space, a sunroom, or a tighter modern build.

It sizes cooling, that is the air conditioner load for the room. The name heat load refers to the heat that must be removed. It is not a furnace or heat pump heating calculation, which depends on outdoor design temperature and heat loss.

Each person radiates body heat. The rule assumes a baseline of two people, then adds 600 BTU per hour for every additional occupant. With two or fewer people the occupant load is zero, so it never subtracts.

A room with heavy direct sun gains extra heat through windows and walls, so the tool adds 10 percent of the area based load when Sunny room is ticked. On a 300 square foot room at 20 BTU per sq ft that is 600 extra BTU per hour.

Ovens, ranges, and other appliances throw off substantial heat while cooking, so ticking Kitchen adds a flat 4,000 BTU per hour on top of the base and occupant loads.

One ton of cooling equals 12,000 BTU per hour, a figure that traces back to the cooling power of a ton of melting ice. The tool divides the total load by 12,000 and reports the recommended tons to four decimal places.

No. A Manual J load calculation accounts for insulation, window area and orientation, air leakage, climate zone, and duct losses room by room. This is a quick rule of thumb estimate meant as a starting point, not a substitute for a professional load calc before you buy equipment.

Not blindly. An oversized unit short cycles, cools unevenly, and removes less humidity, while an undersized unit runs constantly. Use this figure to narrow the range, then confirm with a Manual J calc before choosing a specific tonnage.

Yes. Every calculation runs locally in your browser with client side JavaScript. Nothing you enter is sent to a server, so the tool works offline once the page has loaded.