[Cougar]

At 24x40x12', my insulated barn is just a bit larger than what you have and open to the rafters. I heated it all last winter with a combo of a propane jet blower and a large Fisher woodstove. The stove is the primary heat, the blower is just for the initial quick heat up. I usually angle the blower slightly down to heat up the concrete directly where I'll be working.
There are two unseen advantages to the woodstove; 1. You can get rid of all your woodworking scraps and cardboard, and 2. It is great to weld near, if I leave the door open most of the fumes are drawn up the flue. In midwinter I really can't get the temp much above 55 or so with just the woodstove, but that is enough for me to work comfortably.
I plan to build a new home on this same large NH lot next summer with a drive under garage and unfinished basement. The floor will have radiant heat in both sections fed from the house superstore boiler in the basement. I plan to have a woodstove as well there, with a convection loop feeding from it into the superstore.
Peter