Work out radiator sizing instantly with clear inputs, formula shown and shareable results.
Radiator duty is commonly set from room volume using a watts-per-cubic-metre figure that reflects insulation standard. Because manufacturers publish output at a 50 K mean water-to-air difference while modern condensing systems run nearer ΔT30, the required duty is divided by the ΔT30 correction factor of 0.789 to give the catalogue rating to order.
Radiator duty
Watts = length x width x height x W/m³ factor
Catalogue correction
Catalogue W at ΔT50 = required W / 0.789 (ΔT30 correction)
Watts = length x width x height x W/m³ factor. Radiator duty is commonly set from room volume using a watts-per-cubic-metre figure that reflects insulation standard.
A radiator emits less heat when the water is cooler. Sizing on the ΔT50 catalogue figure while running at ΔT30 leaves the room roughly 20 percent short of its design output.
This calculator takes 4 inputs: Room length, Room width, Room height, Insulation standard. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.