"Andy Hall" wrote in message
...
On Sat, 18 Sep 2004 16:17:55 +0100, "Tom"
wrote:

Most manufacturers seem to recommend setting flow rates in CH systems to
achieve a rise of 11deg across boiler, why is this? is it the most
efficient
setting for heat transfer?
Tom



This is the case for conventional, non-condensing boilers and
represents the optimum for the heat exchanger. In fact the general
design rule is to have 82 degree flow and 70 degree return.
This also avoids the risk of the boiler entering condensing mode,
which for a conventional boiler would result in corrosion.
snipped

Thanks for that, The background to my question is that I'm contemplating
redesigning my CH system in a bungalow I moved into some 6 Months ago; since
4 of the 6 rooms are subjected to high solar gain at different times of the
day I'm attracted towards using TRVs on the rads in the 4 rooms which make
up approx 80% of the total heat load.
I'm further minded to install a Grundfos Alpha pump, however, I'm undecided
as to the control mechanism i.e. a flow switch as advocated by IMM in a
previous thread or to rely on the boiler stat set to 82degC as you stated.
I'm anxious to avoid short cycling of the boiler.
I'd be gratefull for your counsel.
Regards Tom
..