garage heat install

[DanC]

I have a choice of two different heaters to put in my garage. One is a unit that hangs from the rafters, the other is a unit out of a house. Both are GFA. The rafter unit is appealing in that I wont have to build any ducts. Either unit has the round vent (?) that needs to be vented outside. What do I need to know to run the vent pipe out? Things like clearances, roof/ceiling exit, any limits on 90's, etc...
The house unit is appealing in that I could run ducts to all of the shop, but I dont plan to right now, can I just build one large duct on the top of the unit to blow out into the shop (essentially it would be just like the rafter unit then, heating the whole shop from one spot. I assume on this unit the opening of the bottom is for intake and I'll have to build a plenum that holds a filter and the warm air is discharged out the top of the unit?? Do these things have any minimum clearances or can I mount it right in the corner? I plan to mount it X inches of the ground to get above the explosive fumes.
Which unit would be better to heat my 24x26 garage?? I basically need/want to know how to do everything myself before I pay a pro to come in and make sure its all good/safe to use. thanks-

[Goobzilla]

Which rafter mounted unit do you have? Got any pics? Most owner/installation manuals are available on the net with a little snooping around, unless it's a really old unit. I would think with a garage that size you really wouldn't need a lot of ductwork, but then again MT gets pretty darn cold.

[DanC]

they are both fairly old units, both working but replaced with newer, more efficient units. Yes, MT is cold (and hot) just had about 4" snow here today!