Thank you very much, Gideon. My gut feeling was that such a system
would be practical only a certain amount of time during the year. The
humidity is due to the general tightness of the house and (imo) the
geothermal HVAC system not pulling as much moisture out of the air as a
standard system would have.

We would have to manually disable the system I'm talking about during
times of high humidity outside. The radon is of course a concern as
well. Although I suspect that air would be drawn in thru the bathroom
exhaust fans... but then could add the whole new problem of drawing in
septic air since I suspect that our bathroom exhaust fans are tied into
the waste system vents.

My gut feeling is that dehumidifiers are the only practical way to go
and we just live with the expense of running them (they can add around
$10-$20 a month around here to the electricity bill). We have a small
40pint portable unit in the basement that keeps freezing up. I wish I
knew what size we would really need to do the job properly.

Take care,
Melody

Gideon wrote:
A dehumidifer uses more electricity per hour than an exhaust
fan, but the dehumidifer is going to run a lot less than a fan
set to run automatically by a humidistat which isn't aware of
the ambient humidity. When you consider the heated or air
conditioned air which is wasted by the exhaust fan, then the
dehumidifer is going to be much less expensive to operate.

FYI - my next door neighbors have a humistatically controlled
basement exhaust system that was installed by a basement
waterproofing company. It is extremely rare to walk by the
house and not hear it running. They paid a small fortune to
have it installed (about $1000 !) and they are continuing to
pay dearly as it runs even when the furnace or the AC is running.
That's like leaving a front and back window open when running
the furnace or the AC.