Have a melamine enclosure that somewhere in the process will be getting coated in polyurethane sealer. 40ish sq foot worth.

I dont really have a heated area, and hit upon the idea of my backyard shed with power would fit the thing on sawhorses. Due to the cold, was thinking run a heater in there closed up should keep it nice and toasty. I know the fumes arn't good to breathe, but would they be heavy enough to be like condensing onto the heater and burning up or lighting in the air like gasoline vapor?