This is the heated area of my garage 20 x 36...the sliding doors lead into the unheated part....
Walls are R19...ceiling will be R30+...
I use this 5000/7500 BTU electric heater from Northern Tool
At 25ºF outside it will keep it at 65º on the low setting a about ¼ of the way on the knob
When I get the ceiling insulated...it should work just fine....
(I still have a few loose ends to finish up on)