Quote Originally Posted by Mr Smith View Post
And of course I would have to shut that down too while painting.
As long as the furnace is not in your segregated paint area and you don't have a cold air return pulling from that area you would be fine to heat with the indirect propane furnace, blowing heated air into the paint area. The concentration of paint fumes has to get very high to be flammable, anyway, and you will be ventillating the area to clear fumes, right? Your concern about heat escaping through the non-insulated metal walls is the major issue - I have the same thing in my barn.