Water Heater Recovery Rate
Recovery gph and AHRI first-hour rating from input rating, efficiency, and temperature rise. gph = input BTU/hr x efficiency / (8.33 x delta-T). Per DOE 10 CFR 430 / AHRI 1300.
Formula and source
gph = (input BTU/hr × recovery efficiency) / (8.33 × delta-T). Electric input = kW × 3412 BTU/hr. First-hour rating = recovery gph + 0.70 × stored gallons (DOE FHR convention). 8.33 BTU per gallon per degree F is first-principles water properties.
DOE 10 CFR 430 water-heater efficiency test procedure; AHRI 1300 (residential water heaters).
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