"Andy Hall" wrote in message
...
On Mon, 5 Jan 2004 20:45:48 -0000, "John Stumbles"

I've assumed 220mm brick + 13mm plaster, U=2.0 (from BS5449 - I see Myson
use a figure of 1.8 for this construction).

I would expect the extension to have a fairly large heat loss because
of the external wall area.

(The extension shares a party wall with next door.)
I make its loss though external walls 712W. (Actually that includes a new
2m
extension to the ground floor at the back, which has insulated cavity
walls.)

OK, so that takes out a fair chunk of outside wall area down to a much
lower heat loss.



How have you treated the party walls?

I've assumed next door temperatures of 15 downstairs, 10 upstairs (more
pessimistic than the usual 18 up and down, I know).

Seems reasonably conservative.



So for example my big main room (through lounge) has a party wall area of
2
(party walls) * 7.4m (width) * 2.4m (height) = 35.52m^2, and therefore a
heat loss of 35.52 * 2.0 (U value) * 6 (21C - 15C temp diff) = 426 Watts


In the very first house that we had where I installed heating, it was
also a terrace, although quite a bit larger than this one - probably
about 1.5m wider and quite a bit deeper, with an original 2 storey
extension. There was also a fourth bedroom in the loft - basically
in the apex area of the main part of the house.

The design was done when it was customary to allow 3kW for the HW
cylinder. I can remember that the total heat load, worst case, with
10% allowance came to 20kW and I used a legendary Potterton Netaheat
16-22 wound up to full power. This would have meant that the house
peak requirement was probably around 14kW. I did design assuming no
heating in neighbouring properties though.

My first house was similar to the one you describe and I remember when I did
the calcs it wanted a bit more than a 55K BTUs back-boiler would have given.

However the house in question is heated by night storage and it's generally
as warm as toast (during the day, when I've been working there) in the big
main room which has only one storage heater, which can't be chucking out
more than a couple of kW. From that point of view the figures seem
reasonable ... but I'm still not happy with it. :-(


--
John Stumbles
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Pessimists are never disappointed