On Thu, 22 Jan 2004 01:15:45 -0000, "IMM" wrote:


"mike ring" wrote in message
. 252.50...
Andy Hall wrote in
:


You can do the sums on this.

No, I can't, you do them

Calculate the heat loss for the area of the ceilings.

For a pitched roof plus 100mm of insulation, the U value is 0.35

So, let's say the house is 7m square for the sake of argument.

Using conventional central heating temperature assumptions of -3
degrees worst case outside and 18 degrees in the upstairs rooms, the
heat loss will be

Area x U x temperature difference

or 7 x 7 x 21 x 0.35 = 360 Watts

If you have 150mm of insulation, the U value falls to 0.25 and the
heat loss will be 257W.

With no insulation, the U value of the pitched roof is about 2.0 and
the heat loss about 2kW.

Ta

However, averaged over the year, the outside temperature is probably
closer to 10 degrees, so assuming continuous heating at 100mm of
insulation the loss is 223Watts and at 150mm about 160W. With 200mm
you would get down towards 120W.

100W of heating by gas at a price of 1.4p per kWh works out to just
over £12 per annum.

In energy terms, if you compare with the heat loss through the walls
and other means, then you realise that the focus should be on other
issues than this.

Thanks Andy, you've confirmed my gut feeling about losses, and also that
one episode of tripping over a pipe and putting a foot through the
ceiling will take a hell of a time to balance against the extra 8"
insulation.

Put counter joists in to make it deeper for more insulation and board over.

Why? In comparison to everything else, it's little more than a drop
in the bucket.


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..andy

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