Given a 40 gallon natural gas water heater, and a shower head with a flow rate of 2.5 gallons per minute. How long should the shower be able to maintain 105°F water temperature?
Assume the average cold water supply temperature is 58.7°F. The tank will be set at 140°F, to avoid Legionella. The tank recovery is typical of a natural gas heater, so it can recover its volume in an hour (40 gph in this case).