Radiator Size for a Room

Calculate the heat output a room radiator needs and correct it for flow and return temperatures, free online.

Room length (m)

Room width (m)

Ceiling height (m)

Insulation level

Flow temperature (°C)

Return temperature (°C)

Design room temperature (°C)

À propos de cette calculatrice

Room heat loss (W) ≈ room volume × a factor of 30–60 W/m³ depending on insulation. Radiators are rated at ΔT50 (mean water 70 °C in a 20 °C room); at lower flow temperatures output falls by a factor of (ΔT ÷ 50)^1.3, so the radiator must be bigger for a heat pump or condensing boiler.