"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?

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.

Jim A