What size Curved bay radiator do I need for a Heat Pump System?

This is a questions we are asked more and more often now.  Heat pumps come in two flavours- Air Source and Ground Source.

Both types operate at a lower heating flow temperature compared to traditional gas or oil fired boilers.  As a result the size of radiators has to be increased to compensate.  

Radiator heat outputs are normally quoted at a figure of D50 degC or D60 degC.

Your Heat Pump installer will be able to provide you with the working temperature of the installed system.  But as an example, if the Delta figure is D30 degC, then you would multiply the heat output of the radiator quoted at D50 degC by a factor of 0.51.

So if the heat output of the radiator is 2000 Watts at D50 degC, this multiplied by 0.51 would give an output of 1020 watts at D30 degC.

2000 Watts x 0.51 = 1020 Watts

Whichever way it is done, it is crucial the radiators are sized correctly, otherwise they will never get the room to the required temperature.