Water Heater Input for a Target Recovery
The burner or element input needed to sustain a target recovery rate.
Example
You enter
- Heater type gas_atmospheric
- Target recovery rate (gph) 54.879
- Efficiency 0.8
- Incoming water temp (°F) 50
- Set-point temp (°F) 120
You get
- Input (Btu/hr) 40000
Details, formula, and sources
Input BTU/hr = recovery_gph x 8.33 x rise / efficiency (electric kW = input / 3412). A 54.9 gph recovery over a 70 F rise at 80% needs a 40,000 BTU/hr gas heater; a lighter 25.8 gph duty at 0.98 is a 4.5 kW electric element. Answers 'what input do I need' instead of the recovery from one rating. Steady recovery only - a tank credits stored volume for short peaks. Per DOE 10 CFR 430 / AHRI 1300.
input BTU/hr = (recovery_gph × 8.33 × delta-T) / recovery efficiency; electric kW = input / 3412. The inverse of gph = (input × efficiency) / (8.33 × delta-T).
DOE 10 CFR 430 water-heater efficiency test procedure; AHRI 1300 (residential water heaters).
Free at energy.gov/eere for DOE test procedures and ahri.org for the AHRI directory / TOC.
Estimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.
Field names used by the API: heater_type, target_recovery_gph, efficiency, incoming_F, setpoint_F, input_btu_hr
- Recovery efficiency 0.98 electric / 0.80 atmospheric gas / 0.94 condensing gas unless the user enters the nameplate valueDOE 10 CFR 430 / AHRI 1300 typical
- Steady recovery only sizes the steady input; the first-hour rating credits stored volume, so a tank meets short peaks with less inputDOE 10 CFR 430 FHR test
- Water energy constant 8.33 BTU per gallon per degree Ffirst-principles water properties