BTU Calculator

Your room

TVs, ovens, computers, etc.

Result

Enter your room size to see a recommendation.

How we calculated this

The calculator applies a staged method to estimate the cooling load:

  1. Base load — 500 BTU/m² at a 2.4 m reference ceiling. Taller rooms scale the load linearly by ceiling / 2.4. Internal conservative estimator: base cooling load per m² of floor area at a 2.4 m ceiling for UK domestic rooms.
  2. Sun exposure — multiplier applied: shaded 0.9, average 1, sunny 1.15. Internal estimator: solar-gain multiplier by window exposure.
  3. Occupancy — +600 BTU per occupant beyond the first. Internal estimator: per occupant beyond the first.
  4. Kitchen load — +4000 BTU added when room type is kitchen. Internal estimator: additional load allowance for kitchen heat sources.
  5. Appliances — +500 BTU per heat-producing appliance. Internal estimator: per heat-producing appliance (TV, oven, etc.).
  6. Insulation factor — good ×1, average ×1.05, poor ×1.15. Internal estimator: insulation/glazing-quality factor.
  7. Large glazing uplift — ×1.2 when large-glazing is ticked. Internal estimator: uplift for large glazing / conservatory-style rooms.
  8. BTU to kW conversion — divide BTU/h by 3412.14. Physical constant: BTU/h per kW.

Most UK rooms need between 5,000 and 18,000 BTU. A typical 20 m² bedroom with average sun and insulation needs roughly 10,000 BTU (2.9 kW). Larger spaces, kitchens, south-facing rooms, and conservatories all push the figure higher — this calculator accounts for each factor.

Want to know what it will cost to run? Try the running cost calculator. Comparing two units? Use the efficiency comparison calculator.