BTU Calculator

Calculate how many BTUs you need to heat or cool a room based on its size, insulation level, climate zone, and sun exposure.

Results

Visualization

How It Works

BTU stands for British Thermal Unit — the amount of energy needed to raise one pound of water by one degree Fahrenheit. For HVAC, BTU ratings tell you how much heating or cooling capacity a system provides. A room that is too large for the unit will never reach a comfortable temperature. A unit that is too powerful will short-cycle, turning on and off frequently, which wastes energy and wears out the compressor. The general rule of thumb is 20 BTU per square foot, but insulation quality, climate, sun exposure, and the number of windows all shift that number. Getting the right BTU rating is the single most important step in choosing an HVAC system.