Can anyone point me towards an Internet resource which gives
information about boiler size to square footage of property for a
domestic CH system? Or alternatively comment on the following?

I visited a property today to investigate the CH system not giving out
enough heat when it gets really cold. One of the things I found
immediately was that the radiators weren't balanced properly (the
return valves were full open on all that I checked), so that's one job
I've got to do.

However, the CH boiler looks like it's well underspecced for the size
of property. It's a Potterton Profile - I didn't think to get the
model number but it just looked too puny to deliver the heat required
for what is a large property - the property has been extended with an
extra floor. Physically it looked like it was the Potterton Profile
40L jobbie:

http://inspiredheating.co.uk/acatalo...FAN_FLUE_.html

If so then it's a 40,000 BTU unit.

What I'd really like to get information on is what size boiler needs
to be installed for a given square footage, if such info is available
anywhere.

Clues anyone?

PoP