Calculate the BTUs needed to heat or cool a room based on size, insulation, and climate. This tool processes all data locally in your browser. No information is ever sent to any server. Completely free, no registration required.
An HVAC BTU Calculator estimates the heating or cooling capacity (in BTUs — British Thermal Units) needed for a room or building based on square footage, ceiling height, insulation quality, window area and orientation, occupancy, and climate zone. Properly sizing HVAC equipment is critical: too small and it can't maintain temperature; too large and it short-cycles (cooling without dehumidifying, wasting energy and wearing out faster).
Enter room dimensions, insulation level, number and type of windows, typical occupancy, ceiling height, and climate zone. The calculator applies Manual J-inspired load calculations to estimate: Cooling BTUs (for air conditioning) and Heating BTUs (for furnaces/heat pumps). Output converts to tons (1 ton = 12,000 BTUs) for AC sizing.
Base Cooling: 20-25 BTU per sq ft (typical). Adjustments: +10% per person (beyond 2), +600 BTU per window, +4% per degree above 75°F design temp, +10% for kitchen, −15% for heavy shade\nBase Heating: 30-60 BTU per sq ft (climate-dependent). Adjustments: −10% for good insulation, +20% for poor, +15% for high ceilings\n1 ton AC = 12,000 BTU/hr
Cooling: 20-30 BTU/sq ft (moderate climate), 30-40 (hot). Heating: 30-40 BTU/sq ft (mild), 40-60 (cold). These are rough starting points; insulation and windows significantly affect the number.
1 ton of cooling = 12,000 BTU/hr — the amount of heat needed to melt 1 ton of ice in 24 hours. Historical term from the ice-delivery era that stuck.
Free online HVAC BTU Calculator — no signup, 100% client-side processing. All data stays in your browser.