I had a NewAir G73 heater installed in my shop. My shop is 27' x 32'. I has two garage doors and an entry door. The shop has two insulated windows and is insulated. When I turned the heater on, the outside temperature was 44 degrees. and the inside temperature was 47 degrees. I set the thermostat to maximum. It took 1 hour and 40 minutes for the inside temperature to get to 60 degrees. I then lowered the thermostat until the unit shut off. The heater came back on when the inside temperature was 59 degrees. .