BS EN 442 — Radiator Heat Output

In short: BS EN 442 is the European standard governing how radiator heat output is tested and published — at ΔT50 (75°C mean water temperature, 20°C room), which is the figure shown in UK radiator catalogues.

What BS EN 442 covers

Since 2014, all UK radiators must be tested and rated to BS EN 442 at ΔT50, so catalogue BTU/watt ratings are directly comparable between manufacturers.

For heat pumps, which run cooler, the ΔT30 declaration applies — a radiator delivers far less than its ΔT50 output at lower flow temperatures, so it must be sized up.

Matching a radiator's ΔT50 catalogue output to a calculated room heat loss is the core of correct sizing.

Official source: BSI Knowledge — BS EN 442. Figures on this page are a plain-English summary for estimating purposes — always refer to the published standard for compliance.