Installed Hoyt 40HM-EV water heater. The documentation states 34000 BTU is required to heat 28.6 gallons per hour at a 100 degree F. rise. My calculations indicate 17000 BTU needed. However, my data is not factored by an efficiency rating. Therefore, I must assume the Hoyt heater efficiency is 50%. Can some tell me what efficiencies are normal for gas hot water heaters.
Did you calculate at 70, 80, and 90F rises in temperature? The incoming water is colder in the winter and warmer in the summer, so the rise changes. Your calculation would be for warmer ground water temperatures. An average betweeon 70 and 90 would be 80.
40 8.33 80 = 26,656 btu. 26,656 divided by 34,000 = .78 which is about where many water heaters are near – about 80% efficiency.