Depends on the efficiency rating, but I'd say it's gonna use a bunch! I got a 90,000 BTU natural gas furnace in my garage, partly insulated. Gotta finish that someday...
How big is the one in your house? If it's close, use the info they give you on the monthly bill and divide by however much time you think you'll be out there, 50%, 66%, 100%.
100,000 BTU will heat about 1500 sq. ft. pretty well.
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Don't tell people how to do things. tell them what needs to be done and be surprised by their ingenuity. -- Gen. George S. Patton
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