Garage heating capacity
Looking to add a heater to my 2 car garage. It is well insulated and has an insulated door, 1 east facing man door and 2 3x5 south facing windows (southern indiana). It's right at 600 SF with about 10.5' ceilings.
Is a 30K BTU wall heater with blower such as a Procom MD300TBA sufficient for this or should I go with a ceiling mounted 75K BTU heater? The wall heater is significantly cheaper and would be much simpler to mount and run gas too since the gas line is stubbed out of the wall.
I've seen that 35 or 40 BTU/SF is a sort of rule of thumb but I'm not sure how to do the manual J calc and also wasn't sure how the higher ceilings would play into that.
Any recommendations? I'm not looking to keep it 90+ just around 60-65 when I'm working on something. will the 30K heater take an inordinately long time to heat?