Colman mobile home gas furnace to use in my garage/shop

Colman Direct Vent air furnace (sealed combustion) Model# 7970-656/d Two questions. First, since this is a sealed combustion furnace, can I use it to heat a garage? Forget ''code'', there is no building code here. The insurance company just called and said it's OK to use in the garage does that sound right? I question this becasue the guy said "sealed combustion" has nothing to do with it being in a garage. Everyone else told me they use only sealed combustion in a garage where there may be fumes from gasoline, stain, paint, or other solvents.

Second, what are the specs. for the exhaust and air intake vent/flue? It's the exhaust flue inside the air intake pipe. More specifically, does it have to go straight up a certain height before going to a 90 angle and outside. How far can I make the flue pipe run? Also once outside how high does it have to go or can I use one of those... things that just stick out the wall, or is that only for a condensing furnace? If I go out low on the gable end, do I still have to go out above the roof even if the gable overhang is 10 feet up? Sorry for so many questions.