I used this heater in combination with a circulation pump to heat a 750 gallon baptistry at my church. Originally, the baptistry was supplied by a 30 and an 80 gallon water heater setup which required a procedure to fill and would leave the water chilly for batisims. I removed the water heaters and installed the pump/heater system. After filling the baptistry with 62掳 water, it took 11 hrs to heat to 83掳 which will probably be the temperature needed. I monitored the progress of the water temperature rise with an infrared thermometer and marked on the dial thermostat at 70, 80 and 83掳 so we can set a minimum temperature. Now we can fill the baptistry, turn on the pump and heater and next morning have warm water automatically! The only issue with the heater was the tube was kinked from the factory on the flow switch which would not allow the heater to come on. I used thicker walled, weed eater replacement fuel line that allows the bend needed without kinking. Because of the factory defect of the thin walled, kink prone flow switch tubing issue, I rated the heater at four stars. Time and use will determine longevity of the heater.