[D&M2]

I went with a ventless LP heater as I did not want the hassle of putting a vent pipe. My garage is smaller than your's at 22x22. The heater that I got can be either free standing or hung on the wall. The hose is long enough that I could move it to where ever I am working on something but it does such a good job even in really cold weather that I just leave it where it is and turn it up when I plan on working in the garage. I have left it on all the time when I planned on working in the garage and, at the lowest setting, it keep the garage at 50-55 even in the coldest weather that we have had the past couple of years. When I have turned it down to just the pilot and then turned it up for ad hoc work, it was warm in less than 30 minutes.

Right now I have the unit in free standing mode but will probably wall mount it in the near future just to gain some floor space.