In the fall of 2016 I installed a 60k BTU Modine Hot Dawg that has sealed combustion chamber. so far I've been VERY happy with it. my shop is about 1000sf w/ 8.5' ceilings in an existing barn that i just built out and insulated over the past year. 3.5" Roxul in walls and 6" Roxul in the ceilings 3" rigid over the original wood floor with 2 layers of 3/4"OSB over that.
I've been keeping the programmable Tstat at 50 and so far it has been very comfortable to work in even with the this Maine winter we're in the midst of. It seems to run somewhat frequently, but not for very long. Its so nice to have a space that is always comfortable to walk into. No worrying about cans of finish freezing, or applied finishes curing, its better for my cast iron etc...
Cheers,
NWB
"there is no such thing as a mistake in woodworking, only opportunities to re-assess the design"