BTU Calculator (Heating & Cooling)

Calculate BTU requirements for air conditioners and heaters. Properly size your HVAC system for maximum efficiency.

Regular occupancy

Base BTU = Square Feet * BTU per sq ft\nCooling: 20 BTU/sq ft\nHeating: 30-50 BTU/sq ft (climate-dependent)\n\nAdjustments:\n- Ceiling height: *(height/8)\n- Insulation: poor +15%, good -10%\n- Sun exposure: sunny +10%, shaded -10%\n- Occupants: +600 BTU each (after 2)\n\nAC Tonnage = BTU / 12,000
Example (Cooling):\nRoom: 20ft * 15ft = 300 sq ft\nCeiling: 8 ft\nInsulation: Average\nSun: Sunny\nOccupants: 2\n\nBase: 300 * 20 = 6,000 BTU\nSunny: +10% = 6,600 BTU\nTotal: 6,600 BTU\n\nTonnage: 6,600 / 12,000 = 0.55 tons\nRecommended: 6,000-8,000 BTU window unit

What is BTU and how does it relate to heating/cooling?

BTU (British Thermal Unit) measures heating or cooling capacity. 1 BTU = energy to raise 1 pound of water 1degF. Higher BTU = more heating/cooling power. AC: 12,000 BTU = 1 ton. Typical room needs 5,000-12,000 BTU AC. Furnace: 40,000-100,000+ BTU for whole house.

How many BTU do I need for my room?

Basic rule: 20 BTU per square foot for cooling, 30-60 BTU/sq ft for heating (varies by climate). Adjust for: ceiling height, insulation, windows, sun exposure, occupancy. Example: 300 sq ft room = 6,000 BTU AC. Too small = won't cool. Too large = short cycling, humidity issues.

What factors affect BTU requirements?

Room size, ceiling height (standard = 8ft), insulation quality, number/size of windows, sun exposure (south/west = more), climate zone, number of occupants, heat-generating appliances (computers, kitchen), air leakage. Add 10% for sunny rooms, 10% for kitchens, 600 BTU per additional person.

What is the difference between heating and cooling BTU?

Heating BTU is higher because: heat rises and escapes, greater temperature differential (70degF inside vs 0degF outside = 70deg diff vs 95degF outside vs 70degF inside = 25deg diff), air infiltration more significant in winter. Heating: 30-60 BTU/sq ft. Cooling: 20-25 BTU/sq ft.

How do I convert BTU to other units?

AC capacity: 12,000 BTU = 1 ton. Power: 1 BTU/hour = 0.293 watts, 3,412 BTU = 1 kWh. Heat: 1 therm = 100,000 BTU (natural gas billing). Example: 24,000 BTU AC = 2 tons = ~7,000 watts. For energy costs, convert BTU to kWh or therms.