🌡️ Room BTU & HVAC Sizing Calculator

Estimate the heating and cooling load for a room: area, ceiling height, insulation, sun exposure, occupancy and climate all move the number of BTUs you need.

Rules of thumb used

Cooling starts at about 25 BTU/hr per ft² and heating at about 35 BTU/hr per ft² for a UK/mild climate, then scaled for ceiling height, insulation, sun and occupancy (add ~600 BTU/hr per extra person). 12,000 BTU/hr = 1 ton of cooling. This is a planning estimate — a proper Manual-J / room-by-room survey is needed before installing kit.