I have a 30x40 outbuilding, with 2x4 framed walls, standard roof with shingles, etc. Walls have standard batt insulation and the attic has blown-in cellulose.
I heat it with two 30k btu propane "Reddy Heater" style heaters. They get the place up to 60 degrees pretty quick. Portable, no venting, very convenient.
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