Need advice installing a propane shop furnace

[ning]

Seems likely to me that you're going to get substantial heat stratification - heat rises, you're on the floor - so installing some fans may be helpful as well. Could be that enough cold happens at the roof that the air in the place is similar from man-height to higher; also a fan moving air while keeping the temperature more consistent it may make it feel cooler because of the air moving past skin. That's something that can be added later if you find it to be the case.

Found this, it may be helpful: Heater Size BTU Calculator - Heat Wagon Portable and Construction Heaters

For 42x60x14, assuming the building is "fairly tight" (heat retention, ranging from Very Loose/Loose/Fairly Loose/Fairly Tight/Tight/Very Tight) 60° inside desired temp and 20° outside temp, we get 80K.
If you want 50°/0° with a "fairly loose" building, it says 128K.

You're going to have to decide how tight you think the building is.

 

[5030]

I have ceiling fans (attached to the lower chord on the trusses) in both shops to move the air downward and to provide circulation as heat rises. I just bought 4 blade generic fans, nothing fancy. I believe I got them at Menards for under 50 bucks each and they are 3 speed. They stay on low all the time.