I understand how the btu of a room can be calculated, so I can now choose my radiator(s) accordingly! but upon selecting the radiator(s) I discover that the btu output only depends on the btu output of the boiler, which are calculated as Delta T30, Delta T50 or Delta T65 ....so in order to have the correct amount of btu's coming off the radiator(s) that I pick, how do I find out what the Delta T is of my boiler? I have an IDEAL LOGIC HEAT 18 and I have the manual, but no where does it state the Delta T figure! my question is this... is there a way of working it out from the information within the manual or does someone out there know what the Delta T of said boiler is?