Recovery Rate / First-Hour Rating
Two related capacity measures: recovery rate is how fast a heater reheats water, and first-hour rating is how much hot water it can deliver in the first hour of heavy use.
Recovery rate is the number of gallons a water heater can heat per hour through a given temperature rise. A gas heater with a high BTU burner recovers faster than a standard electric model, which is why a 40 gallon gas unit can sometimes out-serve a 50 gallon electric one during back-to-back showers. The first-hour rating combines the tank size with that recovery speed to estimate how many gallons of hot water you can actually pull in the first hour starting from a full, hot tank.
For sizing a heater, the first-hour rating often matters more than raw gallons. A household that showers one after another in the morning is testing first-hour delivery, not total capacity. Two homes with identical 50 gallon tanks can perform very differently if one has a faster-recovering gas burner. This is why simply matching the old tank size can leave a growing family short, and why the rating appears on the yellow EnergyGuide label.
Recovery also explains the wait after heavy use. Drain a tank with a long shower and a load of laundry, and the recovery rate sets how long before there is hot water again, often 30 to 60 minutes on electric, faster on gas. Tankless units sidestep the question entirely since they heat on demand, which is part of their appeal for households that consistently outrun a tank.
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- Anode Rod : A sacrificial metal rod inside a tank water heater that corrodes in place of the steel tank, protecting it from rust for as long as the rod lasts.
- T&P Relief Valve (TPR) : A safety valve on every tank water heater that releases water if temperature or pressure climbs too high, preventing the tank from rupturing or exploding.
- Thermal Expansion Tank : A small tank that absorbs the pressure increase created when water heats and expands in a closed plumbing system, protecting the water heater and valves.