Water Heater Recovery Time Calculator

About this calculator

Recovery time is how long a water heater needs to reheat its full tank after being drawn down, and it depends on the tank size, the heating element's wattage and the temperature rise required: the energy needed equals the water volume times its specific heat times the temperature rise, and dividing that by the element's power output (after accounting for typical heating efficiency) gives the time in hours. A higher-wattage element or a smaller required temperature rise both shorten recovery time.

Plumbers and homeowners use this calculation when sizing a replacement heating element or comparing water heater models, since a household that regularly runs out of hot water mid-shower usually has a recovery time problem rather than a tank-size problem — a bigger tank does not help if the element cannot reheat it fast enough between uses.

This calculator takes your tank size, element power and the temperature rise needed and returns the recovery time, so you can see how long you would actually wait for hot water again after a heavy draw.