What is First-Hour Rating?

First-Hour Rating is an estimate of the maximum volume of hot water that a storage-type water heater can supply within an hour beginning with the water heater fully heated. It is a function of both the storage volume and the recovery rate (how quickly the water in the tank heats back up) of the water heater. Plumbing pros can use that among other factors to help determine the right water heater for a specific homeowner’s needs.