I want to add two more radiators to the central heating system but am unsure if the boiler is going to be capable of handling this, or if it matters. The boiler is a Sime Friendly Format 80 and is currently heating 6 radiators (all 1200 x 60mm aprox). How can I work out if it can sustain another two?

Simon, November 2005

The boiler is capable of 80,000 BTU's (hence 80 in title).

Each radiator of 1200x600 "uses" around the following BTU capacity based on whether they are single, finned double etc.

3800 - Single
5500 - Single with Fins or double with no fins.
7100 - Double with Fins

Add up your radiator sizing and then deduct this from the 80k your boiler is capable of. I don't know the boiler, but if it is NOT a combi, then you need to allow 10-15K for your hot water. If its a combi, then you don't need to make an allowance for the water.

I would guess your answer is yes, no problems!

Pete K, January 2006