I bought this unit knowing it would not heat the 850 sqft. Of my well insulated shot. So here's the scoop. After unpacking and testing on a workench and heat came out I used the mounting bracket to mark the screw locations on the wall and drilled pilot holes for mounting and put in the screws leaving room to mount the bracket. Step 2 I mounted the bracket to the enclosed strap I mounted earlier. Step 3 I hung the unit and bracket on the wall and secured the screws and plugged it in and turned it on. At that time the outside temp had come up from 28°f to 40° f. The shop was 50°f. In 2 hours the inside temp was 66°f. Mind you the ceiling in the wood shop is an average 10 ft. That's why I give this unit 5*s. Heat output is very good even if it won't fry your face 2 ft in front of it. Very safe and adequate. Temp only 3*s as it does not have a thermostat. Only 3*s because I know a lot of people don't know that a garage heater is not a main source of regulated heating. Noise level got 5*s but if you don't know about garage heaters you'll disagree. This one makes the noise of a 20" shop fan. You can carry on a conversation about 3' in front of it and don't need ear plugs. It's easy to hang and use and can heat better than I thought it would. But if you want 80°f on a 20°f day in an unheated 2 car garage, forget it and buy a 20,000BTU heat pump. Oh yes, actual rating is labeled as 3750 Watt so your 20 amp breaker is plenty good between 208 and 240 volts.