In article
, NT
writes
On Oct 22, 6:50*pm, fred wrote:
In article , chris French
writes

In message
,
NT

100% at 12p/unit versus gas with maybe 85% efficient at 3-4p/unit.

I doubt a gas boiler keeping one rad warm gets anywhere near that.

Agreed, assuming a 1kW rad in a small room even a modulating boiler will
be short cycling its arse off every few minutes, warming up the boiler
and pipes with all that doing to waste.

It could work nicely with a thermal store system but not everyone has
one of those and fewer still have the circuits separated enough to
permit this kind of operation.

Even if 50% of the heat is lost in the pipework to the rest of the
house, most of that heat is saved come evening time. So efficiency is
still fairly high.

The whole object is to avoid heating the rest of the house. Why would
this waste heat hang around until the evening? I expect the energy will
have dispersed to the ether long before then.

Either way I don't see that as the main issue, I view it as bad practice
to design a system that will repeatedly short cycle a boiler. I designed
my system for a long slow burn to avoid the thermal stresses that
repeated cycling inevitably brings and I hope to reap the benefits of
this in a longer system life.

Besides that, the o/p's existing system does not currently support this
mode of operation requiring capital investment in redesign, controls and
rework of plumbing. It appears to me that he is looking for a simpler
fix than this.
--
fred
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