Depending on what the outside water temperature is I get at least 15 to 20 minutes of hot water shower in the summer and easily 10-15 minutes of hot shower in the winter doing similar math to what Gdetrailer does, and this is with a 6 gallon heater. I don't regulate that much though cause I like some decent pressure and do have an oxygenics shower head. I also added the electric heater rod kit and have both the electric on and the gas for quick recycle times. My wife wasn't going to do navy showers either. We only wait about 10 minutes between our 10 minute showers and still get a full hot shower on the third and fourth if the whole family is up for showers like after a smoky campfire.