On Sep 17, 9:56*pm, Big_Jake wrote:
I did a little more research on the topic, and here is a pretty good
article on it. *Looks like the answer is that a "condensing" boiler
operating at high temps is only about 88% efficient, or about 4-6%
more efficient than reliable, long lasting, cast iron.

JK

Thanks for the info - what is the URL for the article?

I have cast iron radiators and big old iron pipes serving them - I
think the system was originally a gravity circulator. When the
weather gets good and cold and the unit runs for a while, the
thermometer on the boiler gets up to maybe 180 or 185; I assume that
is the temperature inside the unit, not the return temperature. I
don't know what the return the temp is. But can't you adjust the set
points so that the system runs cooler (but for longer)? (Or, could
you adjust the pump size or speed so the water has a longer residence
time in the radiators, thus returning cooler?)

Of course there is always uncertainty about gas prices going into the
future, which affects any such calculation. -- H