BTU Calculator
Calculate the BTU rating needed to heat or cool a room.
How It Works
BTU = Area × 20 × (Ceiling height ÷ 8) × Insulation factor × Window factor.
Example
A 20 ft × 15 ft room with 8 ft ceilings, good insulation, moderate windows: 300 × 20 = 6,000 BTU.
Frequently Asked Questions
What is a BTU?
A British Thermal Unit — the heat needed to raise one pound of water 1°F. Cooling and heating are sized in BTU/hour.
Is 20 BTU/sq ft accurate?
It is a good rule of thumb for typical rooms. High ceilings, sun exposure, and poor insulation push the number up.
Should I size to the larger room?
For a single unit, size to the largest zone or use the total square footage of the space it serves.