On Feb 20, 8:31 pm, Fred wrote:
On Wed, 20 Feb 2008 11:34:50 GMT, Roger
wrote:

If my
central heating system is any guide I think you may have some difficulty
in finding any period where both inlet and outlet temperatures of a
radiator are stable.

But the same would be true for most CH systems, so what do people do?

I balance systems so each radiator feels equally hot. Since I'm doing
this for a living (i.e. people are paying me to do it) I don't have
time (i.e. I don't charge them) for spending ages getting everything
right by the book. If it feels right to me and to them and
everything's nice & warm & toasty everyone's happy.

As for 'by the book' there's a lot said about getting temperature
*drops* across rads the same. However a radiator's heat output is a
function of its mean temperature, and it is this which we want to
equalise. Since the flow resistances of the pipework feeding each rad
is probably different (and/or these flow resistances are not in
proportion to the rads' own flow resistances) then getting the
temperature drop across each rad the same should ensure that each rad
is operating at the same mean temperature. In other words balancing
temperature drops are a means to the end of equalising rads' mean
surface temperatures.

IMHO, E&OE, YMMV, TGIF etc...