On Tue, 19 Aug 2008 21:16:54 +0100, Steve O'Hara-Smith
wrote:

It does strike me that it may well be reasonable to use the loft as
a solar collector here.

Where is "here" exactly?

OK, so if ice dams and air conditioning costs are not an issue with you, then
look at the cost/benefit ratio. You can't run potable water directly through an
automotive radiator, so you are probably stuck with a large number of home
heating-type fin tubes. Without active air circulation, they are going to be
very inefficient, so you will need lots and lots of them just to erase maybe 1/4
of your domestic water heating bill. What do you pay now for water heating?
$15 a month? So you might save $4 a month with your inside attic collector. If
the fin tubes plus installation cost you $1000, then you will just break even
after 20 years.

On the other hand, if you installed a real solar collector outside the roof, a
much smaller unit could deliver more heat, and it could deliver that heat
year-round, instead of just in the summer, as with your in-attic collector.
Most of the heat the falls on your roof gets conducted away by the wind. What
remains has to travel through the insulating properties of the wood sheathing.
Then it has to transfer to air without the benefit of active circulation, then
it has to transfer again into your "collector". A collector on the roof
prevents much of the wind-conducted losses and avoids two air-to-solid heat
transfers. About the only benefit to the inside collector, as was pointed out
by earlier posters in this thread, would be to disguise the collector for
appearance sake.


Robert Scott
Ypsilanti, Michigan