The message
from "Jim Alexander" contains these words:

"Andy Hall" wrote in message
...
Yes. There isn't a sudden condensing efficiency orgasm that happens
at the dew point. Efficiency increases with falling return
temperature and exhibits a greater *rate* of this below the dew point.

Hmmm. Preparing for "compulsory" replacement condensing boilers in
May 2005
(two jags bombshell No2) had a holiday project trying to find some
hard data
on this. Failed miserably. Any links to actual data over the full
operating temperature ranges?

ISTR that this was raised on the ng several years ago, possibly during
one of the interminable arguments with dIMM and maybe even back in the
days when he was pretending to be Adam. However finding that item is
beyond me.

Ergo, the objective is to get the temperature as low as possible for
as much of the time as possible.

Yep, unfortunately my radiator system is designed for 70deg mean water
temperature. Works well but has little margin for condensing operation.

Think yourself lucky. I am not sure mine was designed at all but when it
falls to 10 below outside I have to run mine continuously to have any
chance of the temperature approaching 19C at the times I want it to. I
have a round tuit buried quite a long way down the pile that had the
materials necessary for insulating the walls (without robbing me of too
much room space) priced at £1000 with the cost of plastering throughout
on top of that. Not sure if the payback point would be anywhere short of
infinity.

--
Roger