How big of a radiant tube heater for a shop 56' x 36' with 14' sidewalls? It has 18" of blow-in insolation in the ceiling 6" bat insulation in walls. The location is in NE Missouri.

Either the 100000 or the 125000 BTU heater would be fine for this. I would go with a 40' tube; QC Part #22657 or 22659.