The ABCs of Plumbing – First Hour Rating

First Hour Rating (also called first hour delivery) is a measurement that calculates the amount of hot water in gallons a full water heater can deliver in the first hour of operation.

The FHR will depend on a number of variables, including the tank capacity, the source of heat (gas or electric), and the burner or element size. Tankless or on-demand water heaters use a different rating system that measures the maximum temperature rise possible at a given flow rate.

Because the First Hour Rating is an important consideration when selecting a tank-style water heater, the EnergyGuide label will list the first hour rating in the top left corner as “Capacity (first hour rating).” You should select a model with a first hour rating that matches within 1 or 2 gallons of your peak hour demand – the daily peak 1-hour hot water demand for your home.

Need help choosing the right water heater for your home? Call ABC Southwest Plumbing & Air Conditioning, we can help.