Most hot water heat systems have an air eliminator.
Spirovent, or some similar system. So, the little bit of air
into the domestic (drinking) water isn't an issue.

--
Christopher A. Young
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"frank1492" wrote in message
...
Thanks all for your answers to my original post about
changing a
pressure tank. Now the second question.
Removing the old tank should be quite easy because
there is a
shut-off valve at the tank so I should not have to drain the
whole
system. Still, some air will be introduced when the change
is made.
Since the system includes hydronic heat I do wonder to
what
extent air could enter the loop (includes a standard air
scoop and
pressure reducing valve and backflow preventer at input.) My
thought
is that most of the air will pass out the faucets if they
are opened
soon after the job is completed and not be an issue, but I
still
wonder to what extent air could be a problem in the hydronic
loop.
(BTW, the tap water and the water for the hydronic system
are both
heated by an oil burner)
Thanks again for your help. If this was my house I
wouldn't bother
asking all these things but it's not my house and I'd like
things to
go as smoothly as possible.
Frank