On Thu, 22 Jan 2004 17:45:58 -0000, "G&M" wrote:


"Andy Hall" wrote in message
.. .
So people in an average house can spend about £100-200 and save about
£10 a year.

That us actually a good return on the investment and so should be done.

I didn't say it wasn't unless the space lost matters. That can be
worth a lot more than £10 a year.

My point was that there are much larger losses of heat.

Take the same house of 7m square and 5m high. Take out 10% for
windows.

The total wall area is 125 sq m.

Under the worst case conditions of temperature outside of -3 and
inside of 21 degrees then the numbers work out as follows:-

Solid walls U=2.0
===============

Heat loss = 125 x 24 x 2 = 6kW

Cavity walls with no insulation U=1.5
==============================

Heat loss = 125 x 24 x 1.5 = 4.5kW

Cavity walls with insulation U=0.55
=============================

Heat loss = 125 x 24 x 0.55 = 1.65kW


Under the typical 10 degree average outside temperature the figures
become 3.25kW, 2.44kW and 894W respectively

So looking at cavity insulation or not in the cavity wall, there is an
energy saving of 1546W.

At a gas unit price of 1.4p and assuming 24*365 heating at 10 degrees
outside (which was the basis of the £10-12 figure) then this comes to
a saving of £190 per annum.

Typical costs for cavity insulating a house are about £1000 so the
payback is in 5 years rather than the the 10-20 years of incremental
loft insulation.

The difference is obvious and significant.




..andy

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