My garage in northern UT has 1 2000 watt heater and it will maintain a comfortable working environment when it is only 10 or 20 degrees out. Several friends have hot dawgs and they work great. My mother in law's condo is heated with the hot water heater. It's about 90 gallon and has the standard inlet and outlet on top and two ports on the side the supply the recirculation pump for the forced air furnace. Does a great job on about 1200 sq ft.
Dave
Dave