In article ,
Bill writes:
In message , Andrew Gabriel
writes
In article ,
Bill writes:
There is, of course the ancillary question about why, if it's a
condensing boiler, we see so much 'steam' from it. If it were condensing

You can't see any steam from it - steam is invisible.
You see the water droplets as a result of condensing the steam.

fully, surely we should see no visible exhaust. Are we losing huge
amounts of latent heat here? Is a second stage condensing process worth
looking into?

That's why I put 'steam' in single quotes. What I was thinking was that
there might be more real steam in the output than there should be, and
that this steam was condensing into what I see after it left the flue.

That will happen. The flue gas will be emitted at about 5C hotter
than the return water temperature, which is going to be about 55C
if the boiler is setup properly. It will be 100% humidity. When it
mixes with the outdoor air at, say, 10C, it will cool and not be
able to hold as much moisture, so a little more will condense out.
Exactly the same thing happens when you breath out in cold air and
you see a mist.

What comes out does feel quite hot, so I'd have thought that a further
heat exchanger stage might be worthwhile.

What temperature is your boiler set to?
Maybe you are running it too hot to be running in condensing mode.
If you have a thermometer on the return temperature, what is it?

If the condensing boiler were
not condensing every bit of steam, this could also capture the residual
latent heat. Are there such things as add-on heat exchangers or would
this have to be a bodge it and see winter project?

You can always extract more. You could put a unit on the flue and
condensate drain which captures and freezes the water, and thus
also extract the latent heat from that. It's really a question of
where you sensibly stop. The heat output from freezing the
condensate would be difficult to use effectively.

Running the boiler at the lowest temperature you can get away with
is realistically the best you can do. I run mine at 45C flow 40C
return, but I have radiators suitably sized to heat the house with
the water at that temperature.

--
Andrew Gabriel
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