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What is the First Hour Rating (FHR) of a water heater?
Sunday, November 18, 2018
The U.S. Department of Energy requires that the FHR of storage water heaters be printed on the yellow EnergyGuide on the side of the water heater. The First Hour Rating is defined as “the number of gallons of hot water the heater can supply per hour, starting with a tank full of hot water. We are not sure why, but an EnergyGuide label is not required for the new electric heat pump water heaters. Here’s two examples of an FHR rating from a gas and electric water heater.
Gas water heaters tend to have a higher FHR because they can provide more BTUs of heat faster. The variables that affect the FHR are size of storage tank, source of heat (gas or electric), and size of gas burner or electric heating element.
The purpose of the FHR rating is to help you determine if a water heater you are considering buying will meet the needs of your household during the “peak usage hour,” which is usually the early morning. Here’s the average gallons of hot water usage ratings for each type use:
- Shower - 10 gallons
- Shaving - 2 gallons
- Hand Washing - 4 gallons
- Food Prep - 4 gallons
- Automatic Dishwasher - 6 gallons
- Clothes Washer - 7 gallons
Adding up all the water usage gallons in your family’s morning or evening peak hour usage will tell you if it falls within the FHR of the water heater. So three showers, one dishwasher cycle, and a food prep equals 41 gallons. Add one more shower and you are close to the limit of the electric water heater shown above, and anything more beyond that puts your over the recovery capacity of the water heater—and you need a heftier unit.
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