Heat loss & emitters
Required catalogue radiator output
- where
- required catalogue output (W)
- required room output (W)
- operating mean-water / room difference (K)
- catalogue rating difference (K)
- manufacturer exponent
Explain this equation
Works out the catalogue output a radiator needs so it delivers a required output at your operating temperatures. Use it when picking radiators for a lower flow temperature.
P is the heat the room needs. ΔT is the mean-water to room difference the system will actually run at. ΔT_rated is the catalogue test difference, often 50 K. n is the manufacturer's exponent.
It is the radiator output equation turned around. (ΔT / ΔT_rated)^n is the fraction of rated output you get at the lower temperature, so dividing the need by that fraction gives the catalogue size.
Sense check: 1500 W needed at ΔT 30, rated at ΔT 50 with n 1.3, needs about 2900 W of catalogue output, nearly double.
Watch out: this does not calculate room heat loss. Pick a real product from its published data.
Enter your values to see the result.
Good to know
Choose a real product using its published performance. This does not calculate room heat loss.
Sources
Results are arithmetic only. Worked examples are not recommended design settings. This library does not provide automatic gas pipe selection, live gas tightness tests, purging procedures, combustion acceptance limits, installation approval or commissioning certification. Manufacturer data and the applicable current method remain essential.