Heater placement
I just had a garage heater installed last month and love it. It's a Reznor 45,000 BTU roof mount heater and it keeps the garage nice and toasty. My garage is 24'x24'x8' and I had to insulate it and poly it as well (I still have to finish the walls in OSB and replace the garage door, but that will come in time) You can see the angle the installers put it on and it seams to blow the heat around well.
The Reznor is the most efficient garage heater you can get. It's 86% efficient I believe? It's not loud either.