In 1978, I bought a used 25,000 btu wall mounted, through the wall vent and
air intake propane furnace. I paid about $30 at the time for brand new
exhaust intake piping. I heated my 20 X 20 foot and 20 X 24 foot shops with
it until 1992 when we built a new house and it was still running fine in
west central Wisconsin. I had pretty well insulated walls; 8" of
fiberglass, one inch of foam in walls and 10" of fiberglass and one inch of
foam in ceilings. I put one inch of foam 2 feet deep around the concrete
floors all the way around. No trouble at all getting the place up to 70
degrees plus at -30F. I replaced in with a new 35,000 btu unit in 1992,
The new one is a Williams wall mounted furnace with a vertical chimney/fresh
air intake, which also has an adjustable rear vent to heat a new breezeway.
Again, it works just fine- no concerns at all with condensation, even though
I keep the temp down to about 60 degrees.
I built a woodshop in another part of that building about 6 years ago
and added another furnace of the same type. I'd do it again.
I know that one poster said he didn't have condensation problems with an
unvented propane heater, but I certainly had it before I did the above, and
I worked part time in a place that used that form of heat and it sure did
have condensation.

Pete Stanaitis
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