I have a small shop, just 18 x 30. I just bought a portable 40,000 btu forced air propane heater on Ebay, $69 plus shipping. I have used a similar kerosene fired heater in the past and it warmed it up nicely. I like the propane better because it is cleaner and does not have that smell. Our weather does not get all that cold, but 38 degrees is still pretty cold to work in! I expect the new heater this week or next, I'll put in a report once I have tried it out.

Pat