I'm self refurbing a ground floor flat in a mid-terrace property (built around 1880!). The renovation is extensive and goes back to bricks and joists.

After destroying it, I've began to build it back up. I've taken accurate measurements of each room, inputted these into 3 different online BTU calculators and am repeatedly coming to a figure of 30,000 BTU, or so.

The boiler is a Potterton Combi, rated at 28kW DHW / 26kW CH Pnc (condensing)...whatever that means. By my maths, 28kW = 95,000 BTU

I have 2 questions:

(1) Is there any harm / negative effect in over speccing and get radiators equivalent to, say, 40,000 BTU?

(2) I don't know whether my system is delta 50 or delta 60 as all the pipework has been ripped out, so I don't know what the inlet / outlet water temperatures would have been...what should I assume, as this has an effect on BTU values