Water Heater Recovery Rate
GPH = (BTU/hr × efficiency) / (8.33 × ΔT). Hot water output rate.
Result
Recovery rate
54.9 GPH
0.91 GPM continuous.
- BTU/hr40000
- Efficiency80.0%
- ΔT70 °F
- GPH54.88
- GPM0.915
Step-by-step
- Useful BTU = burner × efficiency = 40000 × 0.8 = 32,000.
- Per gallon: 8.33 lb × 1 BTU/lb/°F × ΔT = 583.1 BTU.
- GPH = useful BTU / per-gallon = 32,000 / 583.1 = 54.9.
How to use this calculator
- Enter burner BTU rating.
- Enter efficiency (label or AFUE).
- ΔT = setpoint − incoming cold (typically 70 °F).
About this calculator
Water heater recovery rate (GPH = gallons per hour) measures continuous hot water output. Formula: GPH = (BTU/hr × efficiency) / (8.33 × ΔT), where 8.33 lb/gal is water mass. A 40,000 BTU gas heater at 80% efficiency raising water 70 °F: ~55 GPH ≈ 0.92 GPM. Tankless heaters quoted at peak GPM. Tank heaters: tank capacity gives buffer for short bursts (shower); recovery rate matters for long demands (back-to-back showers).
Frequently asked
1 W = 3.412 BTU/hr. Electric water heater 4500 W = 15,354 BTU/hr (much less than gas).
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