"Andrew Gabriel" wrote in message
...
In article ,
"dennis@home" writes:
If its a condensing boiler what produces the mist?

The condensate.

How much don't they condense out and how much heat is wasted because they
don't?

Depends on the return water temperature.

I just wondered when a new super condensing boiler was going to be
required
if the condensing ones are so bad they leave troublesome plumes?

The plume is as a result of condensate. If it was still steam,
that's invisible.

And if it had condensed and given up its heat to the heat exchanger it would
drip off and not be a plume.