I installed a gas-fired wall-mount furnace in my garage 2 years ago and
it has worked out well. It's a unit like someone else described earlier
in this thread: the intake air and exhaust gas come and go through the
wall in concentric ducting. There is essentially no open flame hazard,
because the combustion chamber is open only to outdoor air. (There is a
small pilot flame site window cover with a cover clamped over it.)
It cost about $600 for the unit and another $600 for help from a gas
fitter to run gas line from one corner of the basement to the other,
then 20' or so of pipe in the trench. I dug the trench. As soon as the
pipe was in the trench the earliest and snowiest winter in memory
started. I refilled the trench weeks later with frozen chunks of earth
during a "thaw".
I believe the same units are available in propane. My furnace is about
33,000 Btu (I think) and you wouldn't want any less capacity than that
for a two car garage. I bought the optional fan, but it doesn't exactly
give a blast of warm air on a 20 or 30 degree day -- it takes time to
warm up in those conditions.
As far as humidity goes, you'll need a heater if you want the
dehumidifier to run much in the winter. They're likely to frost up
below about 50 deg., so they're either set to stop running at low temps
or an electric defrost circuit comes on.
Any time you add heat to the air, the air will then hold more moisture,
so the relative humidity will go down. I think the rust problem that
Chip mentions occurs where a car regularly comes into the garage wet and
salty. The chemical reaction of rusting is accelerated when the salt
water cocktail is heated. I don't think that would be a problem where a
car stays in the garage -- the heat should help to keep the moisture
away, unless there is a big source of moisture such as a leaking
concrete wall.
-- Steve Manwell
Melrose, MA, but lived through many a salt-bath winter growing up in
Syracuse, NY.
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