Mark, much as most of us just hate you for having a 55'x 50 hangar.....I have to put in my $.02

a couple ideas nobody has forwarded.
because it's so big, I have to ask.....how many places can you stand, or work, at once?
Perhaps just heated boots?
I have a 3 car garage, but I work in front of the bench 99% of the time. So a $60 radiant heater sitting on the floor warms me up in about 5 minutes. by lunchtime, the bench, tools etc. are all warm to the touch. Radiant kicks butt.
Your 'contractor' should be put in that special place where they put people who suggest what's quick, easy, and cheap...for them. They don't have to live with the result. Big hanging forced air units are 1940's tech, and they were stupid then too!..... good for wasting a LOT of energy ( $$$) and heating the air at the ceiling. Sure, fans can push it down a bit ( more $$$ to run) but the draft is uncomfortable.
Look at the big hangars, like Buffalo Airways in the faaaaaaar north, ( Yellowknife etc.) they have black pipe radiant tubes overhead. It warms the planes, then the floor, then the air.
If you have a 'tool zone' you could put a wooden subfloor in the area only, or even build up a platform, 3" thick, insulate it, and put radiant floor panels in it.
.....hang a clear poly curtain/ceiling enclosure, and you'll have a shirtsleeve environment for a few bucks an hour.
If you have the choice, and budget, radiant first, for quick heat, then slab heat, but put in a LOT of zones, so you can mitigate leaks, and only heat the area you are using. You need good thermal breaks at the outside walls and under doors etc....or you lose all that nice slab heat to the outside....unless you WANT to melt the snow on your ramp!?!?? Beats shoveling! ( wait, tell the wife you need a 4-wheel drive tractor too, with a blade, and backhoe, with mower, and a cab, with a towbar, and a/c with MP3 surround-sound, ......ah heck, you probably already have one eh???
