Radiator Balancing - is there an idiots guide?

Same rules apply just a larger delta t on a boiler because of higher flow temps, smaller radiators.

I’m struggling to get my head round the basics still…

If my heat pump is delivering a dT of 5K, but I’m only seeing 3K across my radiators, should I instead be looking at the speed of the pump that’s circulating from the low loss header to the rads? What effect will that have on the performance of the whole system?

[Edit: I checked the speed setting on the pump (Grundfos UPM3 AUTO), and it’s already on the “Lowest relative pressure curve” for radiators]

All the rooms get warm at the same rate, so maybe I don’t need to worry about about balancing?

You are looking for a dt of 5 across your primaries which mean’s potentially your nearest rad maybe only 1 degree and your furthest rad will be 5 degrees because you are losing convected heat from your rads into the room. So as the water is flowing it slowly loses heat around your circuit that’s why flow rate is so important for efficiency along with volume.

FWIW, the forum software enables one to writie dT as


which yields ΔT



yields δT [added by RW]


Not on a two pipe system.

All rads will be ΔT 5 degrees near as makes no odds; as the losses from the distribution pipework are minimal compared with the output from the radiators.

I would have to disagree slightly in as much that if you had 2 pipes and no radiators then yes you could obtain and keep your deltaT of 5, but when you take into account convected heat and heat loss through the pipe work you will vary the balancing to take that into account. Not all rooms will take the same amount of convected heat out some more than other which means that your return will be cooler enlarging your deltaT. You cannot dismiss those factors in your balancing particularly at low flow temps. It’s not so important when you have a gas boiler pumping out at 75 degrees