Have a reddy heat jet heater that was on sale for about 100 at lowes one year. Suppose to heat a 5000 sqft area, doesn't take long to heat our 1200 sq ft shop
We have it on a shelf up near the ceiling so the jet isn't constantly blowing on you and an old fan from a school that was shut down to pull the heat down works pretty good, of course our shop is pretty well insulated so even if its below freezing outside once we get it warm inside just turning the heater back on for a few minutes every couple of hours keeps the shop warm if the doors aren't constantly being opened and closed.