Everybody -- thank you very much for your helpful replies.

I got some additional feedback from a client of mine who is also an
experienced contractor, and he verified that this is a rather standard
practice among contractors here (San Francisco) to use a home's heating
system to help dry paint and joint compound or what-have-you.

A little more explanation: in San Francisco, our average temperature is
pretty mild year-round. It gets to be about 65-70 degrees during the
day and 52-55 degrees at night.

http://www.cityrating.com/citytemper...=San+Francisco

Plus, our marine air here is pretty moist (fog and so forth). So it
can be difficult to keep a house DRY inside when the heat isn't being
used.

So, it IS pretty common that contractors here in San Francisco will run
heat (and/or lights) at night to keep the temp up and help things dry.

That said, my client/friend said that he understood my concerns
regarding the new furnace. He suggested that the General needed to be
real careful with all the airborne dust and so forth that could
possibly get into the system.

So I did as had been suggested to me, I got the General to accept
responsibility for the well-being of our new furnace and also to
install an extra "pre-filter" over/before the cold air return so that
particles don't even make it into our new system.

So, that's solved, the contractor is taking these steps and we've
authorized him to run the heater at night to keep the temp up and let
the inside of our house dry out.

Thanks again for the input.

~r