Water Heater Recovery Calculator
Calculate water-heater recovery capacity from temperature rise, efficiency and either GPH demand or heater input.
Temperature rise
90 °F
Useful water-heating load
75 MBH
Required heater input
93.7 MBH
Recovery from known input
107 GPH
Recovery is only one part of water-heater sizing. Storage, peak draw, recirculation losses and manufacturer first-hour ratings may govern.
Turn the calculation into a complete design workflow
Use the free result as a quick engineering check, then continue into MEPFlow for connected system design, sizing and project calculations.
How the Water Heater Recovery Calculator Works
Heating one US gallon of water by one degree Fahrenheit requires approximately 8.33 Btu. Multiplying gallons per hour by temperature rise and 8.33 gives the useful heat transferred to the water.
To estimate required heater input, divide useful heat by thermal efficiency. To estimate recovery from a known heater input, multiply input by efficiency and divide by 8.33 × temperature rise.
Recovery is only one part of water-heater sizing. Storage volume, peak draw profile, first-hour demand, mixing, recirculation losses, standby losses and manufacturer ratings can all govern final equipment selection.
Calculation basis
Useful Heat ≈ 8.33 × GPH × ΔT
When to Use This Calculator
- Commercial DHW recovery checks
- Storage heater screening
- Boiler-to-DHW capacity checks
- Temperature-rise sensitivity
Engineering Checks Before Final Design
- Use manufacturer-rated thermal efficiency when available.
- Peak storage demand can govern even when recovery is adequate.
- Include recirculation and distribution losses in final sizing.
Frequently Asked Questions
What is water-heater recovery?
Recovery is the rate at which a heater can raise incoming water to the target delivery temperature, commonly expressed in gallons per hour.
Why does colder inlet water reduce recovery?
A larger temperature rise requires more heat per gallon, so the same heater input produces fewer gallons per hour.
Does efficiency affect required input?
Yes. Heater input must be higher than useful water-heating output when efficiency is below 100%.
Does this choose storage tank size?
No. Storage sizing requires the building's peak draw profile and recovery/storage strategy.