Water Heater Recovery Calculator

Recovery Rate is the heater's BTU output divided by the energy needed per gallon, and that per-gallon energy need rises with the temperature rise (Set Temperature minus Inlet Water Temperature). A higher thermostat setting — say 140°F instead of 120°F — widens that gap, so the same burner produces fewer gallons per hour even though its BTU output hasn't changed.

Thermal Efficiency is the percentage of the burner or element's rated BTU input that actually goes into heating water rather than being lost up a flue or through the jacket. Standard atmospheric gas water heaters run around 80%, high-efficiency condensing gas models reach 90% or higher, and electric resistance water heaters run close to 98% since there's no combustion exhaust to lose heat through.

It's calculated the same way the label estimates it: 70% of the tank's rated capacity (the portion assumed usable before cold water mixing degrades output) plus one hour's worth of Recovery Rate. It's a close approximation of that label figure, not an exact match, since actual EnergyGuide testing follows a specific DOE test procedure this calculator doesn't replicate.

Standby Loss here is a fixed 2%-of-BTU-input-per-hour approximation, not a measurement of your specific tank's jacket insulation or age. Real standby losses for standard tanks typically run in the 2-4% per hour range depending on insulation quality and ambient temperature, so treat this figure as a planning estimate rather than a guarantee for any particular unit.