"dennis@home" wrote in message
.uk...
On Tue, 27 Sep 2005 21:57:48 +0100, in uk.d-i-y "Doctor Drivel"
wrote:

The condensing boiler can use 22mm pipe where 28mm would be required
for
a
non-condensing boiler.

Could you explain why there is a difference between the condensing boiler
and a non-condensing boiler?
I can't see why there would be a difference.

It operates at a wider temperature differential.

You can increase the efficiency of a non-condensing boiler. Insert a
blending valve on the boiler return set to 60C (it doesn't go below
dew-point inside the boiler). This is common practice with commercial
boilers using a motorised mixing valve. This mixes system return water with
flow water from the boiler. Design the system to run at 80C flow and 60C
return, and balance the system to achieve 20C across the heat loads. I
would only do this with a one-piece heat exchanger. You can then downsize
the pipes. Note: the makers would always say runs at 80C flow and 10C temp
differential. If you know what you are doing you can greatly improve
efficiencies