Z wrote:

What measurements would one need to calculate radiator output HW output
and henceforth boiler output for a domestic premises.

Room volumes, u values?

Create yourself a spreadsheet with a set of entries for each room. You
need three bits of information to workout the heatloss:

The surface area
The temperature differential
The u value of the surface.

Multiply the lot together to get a figure of watts/hour transferred
through the surface.

(if a wall has a window then subtract the area of the window from that
of the wall, and count the window as a separate surface).

One you know the loss (or gain) through each of the surfaces add them up
to get a nett loss/gain for each room

Lots more info here-

http://www.diydata.com/planning/ch_design/sizing.htm

--
Cheers,

John.

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