After getting my Dayton G53 electric heater (http://www.sawmillcreek.org/showthread.php?t=122266) , I am now looking for further improvements in my garage insulation. I can’t tackle everything this winter due to time and money constraints, so I am looking for the best bang for my time/buck.

It's a 2 car attached garage with 8' ceilings and about 500sf of total area. The garage walls are sheetrocked, but with no insulation (with the exception of the wall that is shared with the house). The ceiling is also sheetrocked, but the attic on top is not insulated. The two garage doors span most of the longest wall and are already insulated with a 1.75” thick rigid foam in between the metal sheets (pre-installed by the manufacturer).

Last weekend, temps went down to the high 20s and the garage was about 40F (without the heater being used). I fired up the heater and had the garage at 50F in about 15 min, but after an hour, it wasn’t getting much warmer than 52. It’s good enough for me to work, but now I am getting ambitious and thinking that 55-60F would be great!

So here is what I have currently in mind:

1) Garage doors: I could add some additional insulation on top of what they already have, but it doesn’t seem like the best first thing to do.

2) I could insulate the attic with some bat insulation. It would be an easy DIY project, and for the 400sf of area, I am probably looking at something in the $300 worth of 30R insulation. I am leaning towards doing this first.

3) I could blow in some insulation through holes in the un-insulated walls (about 400sf of wall area). I have no idea how to do it myself and probably would have to hire someone. Don’t know how much that would cost either.

If you can pick only one of those 3, which one would that be? Any ideas about costs? Any other alternatives I might be missing that would make a bigger impact?

Thanks!