Several years ago a friend took out a working electric furnace . He wanted the then available lower gas bill.
It was a 120,000 BTU 240 Volt heater, with 3 heating elements. I disconnected 2 , a had a 40,000 BTU heater .
I wired the heater with a electric stove cordset and a 40 Amp circuit.
Over the top duct opening I put 1/2" steel hardware cloth and alum window screening.
I put a filter on the intake and finished it off with a wall mounted thermostat .

We epoxy coated the floor, hung a swing , put in a stereo with UREI 809s

With the cars outside we have a place for the grand kids to play. (papa too)

The garage has insulated plaster board walls and cieling, 1" strofome under the slab floor , thermo payne windows facing south, and an insulated 1.5" steel door. We painted it white and that really helped brighten it up.

Don