"Christian McArdle" wrote in message
t...
I've read most of the condensing boiler discussions in this group and as
a
result decided to fit a standard boiler - mainly because of not being
able
to upgrade old radiators to work with the lower return temperature.

Unfortunately, you are misinformed. Although condensing boilers can take
additional advantage of lower return temperatures, they are still more
efficient than a traditional boiler at high return temperatures too. There
is absolutely no need to replace radiators when upgrading to a condensing
boiler. The additional economic benefit is too slight to be worth doing
unless the radiators are being replaced anyway. The condensing boiler will
usually be capable of maintaining the "standard" 82C flow temperature. (My
Bosch Worcester Greenstar II 28HE claims to run up to 88C flow
temperatures).

Also, radiators are sized for outside temperatures of -1C. As this is much
lower than your average temperature, your radiators are usually oversized
anyway and the condensing boiler can turn down the return temperature
using
its internal logic.

What if they put the heat exchanger on the return flow?
That would drop the return temperature even if the old radiators didn't.
Am I being too simple minded?

This heat exchanger should be connected between flow and return as normal
via a zone valve.

Modern condensing boilers have load compensation control that takes care of
rads sized to 80C. The big market is in replacement boilers and the makers
designed to suit. The only case where you don't fit a condensing boiler is
when the plume is a nuisance or there is no drain connection for the
condensate. Otherwise "always" fit a condesning or "no-flame" boiler.





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