CatDog I'm sure your heating contractor will put you in the right direction. He should be able to suggest a nat gas warm air unit to meet your needs. Besides whole house residential sizes there are also apartment sized units that ought to be down close to your garage BTU needs. ( My estimate without seeing your building is between 28,000 to 35,000 BTU/hr heat loss.) Sometimes referred to as wall mounted unit heaters, they are set up with through the wall exhaust venting so no chimney is required. About the only down side to these is you generally have no way to attach duct work for more even heat distribution. But for a garage this is a non factor usually. Local codes may or may not permit open flame devices in a garage and again your contractor will be able to inform you.
Good luck with the project. It will be worth the wait.
Mike
