UK Standard
CIBSE Domestic Heating Design Guide — Room Heat-Loss Method
CIBSE Domestic Heating Design Guide & Guide A (Environmental Design)
In short: The CIBSE method is the UK standard for calculating room heat loss from volumes, U-values, exposure, and temperatures to size heating systems.
What CIBSE Domestic Heating Design Guide covers
Published by the Chartered Institution of Building Services Engineers, it is the recognised reference for domestic heat-loss and radiator sizing in the UK.
Good practice adds a design margin (around 10%) over calculated heat loss to allow for cold snaps and radiator fouling over time.
Apply this standard
Calculators that use CIBSE Domestic Heating Design Guide
Official source: CIBSE — publications. Figures on this page are a plain-English summary for estimating purposes — always refer to the published standard for compliance.