I bought my BlueFlame brand 15,000 BTU heater on Ebay for about $150.00
delievered. This is a ventless type and I have had no problems with
moisture in the garage.

My space is about 1/2 your space, and on a pretty cool day, like 30's,
it would take about an hour to make the space habitable. Therefore
with 2x the space, I would go to a 45,000 btu unit and you should be
pretty comfy in there.

15,000 btu's cost me about $0.50 an hour to run at $2.20us a gallon of
propane.

Alan

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