Victorian mid-terrace central heating

matelodave

Have a look at this - Lower the flow temperature on your boiler to save ££ (theheatinghub.co.uk).

Most radiators are specified for a Delta T of 50 degrees (20 degrees room temp with a radiator temp of 70 degrees (80 degrees flow with 60 degrees return)), so if you reduce the flow temp you'll reduce the Delta T and therefore get less heat out of the same radiator. However provided you get sufficient heat to counteract the heat loss then it will just take longer to heat the room.

 Have a look at the table in this How to calculate the "delta T" for a radiator | AEL Heating Solutions Ltd | ESI Building Services (buildingservicesindex.co.uk) to see how the output changes with Delta T - you get about half the output with a Delta T of 30 (room temp 20 rad temp 50 - flow 60, return 40)

As QrizB says, all you need is sufficient heat,  so you need to specify a radiator with sufficient output at your proposed Delta T. It doesn't matter where the heat comes from but the lower you can get the flow temperatures the less it'll cost to heat the place.

A good analogy is driving at 50mph compared with driving at 80mph - they'll both get you there, one a bit faster than the other but slow and steady at 50 will give you much better mpg than thrashing along at 80