Just at the heating installation stage of a new build. House is about 3000sq ft and planning to run UFH and DHW off a condensing oil boiler. Plumber originally quoted to install a 118,000 BTU (26KW) boiler, now the time has come, he has bought a 88,000 BTU boiler. I'm concerned that the boiler is too small for the job. A couple of UK websites that have boiler-size calculators on them, tell me I should have around 27 - 32KW. He also plans to instal a 200L water tank which I also have concerns about (will be running 3 showers and a bath off it). Any plumbers out there that would be able to tell me if he is way off the mark or not? I dont want to be ripping out stuff at a later stage.