Water Heater Recovery Time

Estimate how long a storage water heater needs to reheat its entire tank after depletion. Supply the tank volume, temperature rise, and burner or element output to see the theoretical recovery time.

Capacity of the storage tank in US gallons.
Desired increase between incoming cold water and delivery temperature.
Rated heating capacity from the equipment nameplate.

Approximate; actual recovery varies with heater efficiency and heat losses.

Examples

  • 40 gal, 70°F rise, 40,000 BTU/hr ⇒ 0.58 h
  • 50 gal, 60°F rise, 30,000 BTU/hr ⇒ 0.83 h
  • 80 gal, 75°F rise, 50,000 BTU/hr ⇒ 1.0 h

FAQ

What does 8.33 represent?

It converts gallons of water to pounds.

Does this assume 100% efficiency?

Yes, real heaters may take longer.

Can I use liters and watts?

Convert units to gallons and BTU/hr before using.

Is the result in hours?

Yes, multiply by 60 for minutes.

Additional Information

  • The formula multiplies tank volume by 8.33 (pounds of water per gallon) and the required temperature rise, then divides by heater output in BTU/hr.
  • Results assume 100% efficiency. Electric and gas heaters typically recover more slowly due to standby and flue losses.
  • Multiply the hour value by 60 to express recovery time in minutes.
  • For metric units, convert liters to gallons (1 gal ≈ 3.785 L) and kilowatts to BTU/hr (1 kW ≈ 3412 BTU/hr) before entering the numbers.

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