Water Heater Recovery Rate Calculator
Find how fast a water heater can reheat. Enter the BTU input, the efficiency and the temperature rise from cold inlet water to your set point to get the recovery rate in gallons per hour.
How to calculate water heater recovery
- Enter the burner or element heat input in BTU per hour.
- Set the efficiency, about 0.98 for electric and 0.80 for atmospheric gas.
- Enter the temperature rise in degrees F to read the recovery in gallons per hour.
Examples
40,000 BTU gas heater, 80 F rise
40,000 BTU, 80 percent efficiency, 80 F rise
About 48 gallons per hour of recovery
Frequently asked questions
What is water heater recovery rate?
It is how many gallons the heater can raise to your set point in one hour. It depends on the heat input, the efficiency and how cold the incoming water is.
How is recovery rate calculated?
Recovery in gallons per hour equals the BTU input times efficiency divided by 8.33 times the temperature rise, since one gallon needs about 8.33 BTU per degree F.
What efficiency should I use?
Electric resistance heaters are about 0.98, standard atmospheric gas about 0.80, and high efficiency condensing gas can reach about 0.95.
How do I convert watts to BTU per hour?
Multiply watts by 3.412. A 4500 watt element is about 15,357 BTU per hour, which you can enter directly into this calculator.
Why does the temperature rise matter so much?
A larger rise needs more energy per gallon, so recovery drops. Winter inlet water is colder, which is why heaters recover more slowly in cold months.
Related tools
Water Heater Cost Calculator
Find the energy and cost to heat a tank of water. Enter gallons, inlet and outlet temperature, your rate and efficiency to get kWh and cost.
Pipe Volume Calculator
Calculate the water volume held inside a pipe in gallons, liters and cubic inches. Enter the inner diameter and length to size flush and purge jobs.
Pool Heater Calculator
Calculate the energy and time to heat your pool. Enter gallons, the temperature rise, heater output and efficiency to get BTU, kWh and heating hours.
Appliance Energy Calculator
Find what an appliance costs to run from its wattage. Enter watts, hours per day and your rate to see kWh and cost per day, month and year.
Aquarium Volume Calculator
Calculate your fish tank volume in gallons and liters from inside dimensions in inches. Set a fill level to estimate the actual water it holds.
Baseboard Calculator
Estimate linear feet and pieces of baseboard or trim for a room. Enter length and width, subtract doorways, set piece length and add waste.