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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Here’s links to a collection of more blog posts about WATER HEATERS:

• Are water heaters required to be raised off the floor? 

• Can a Temperature and Pressure Relief (TPR or T&P) valve be mounted to discharge horizontally?

• Where are gas water heaters not allowed to be installed?  

• Is the minimum size water heater inlet pipe 1/2" or 3/4" according to the building code? 

• Can you use a light switch for a water heater disconnect? 

• How can I tell if a water heater is HUD-approved for mobile/manufactured homes?

• Can you wire a 240-volt water heater with 120 volts? 

• Is it alright to have a shut-off valve on both the hot and cold water pipes at a water heater?  

• What is the minimum clearance to doors and windows for an outdoor tankless gas water heater? 

• What is required clearance for access and working space in front of an electric water heater? 

• Why is the water heater older than the house? 

• Does a water heater need a shut-off valve? 

• Why should a tankless water heater have an isolator/service valve kit installed?

• When was a gas water heater first required to be elevated 18 inches above a garage floor?  

• Can the temperature and pressure relief (TPR) valve discharge pipe for a mobile/manufactured home water heater terminate under the home? 

• What is the purpose of a thermostatic mixing valve above a water heater? 

• Does a tankless gas water heater still work with no electricity during a power outage?  

•  Why do water heaters have a sacrificial anode? 

• What is the difference between a manufactured/mobile home water heater and a regular water heater? 

• Does a tankless water heater require a pressure relief valve?

• When is a water heater drain pan required?

• Why is there water in my water heater drain pan?

• What does it mean when a water heater Temperature/Pressure Relief (TPR) discharge pipe is "trapped"? 

• Can I leave a gas water heater in place when remodeling a garage into a family room or bedroom? 

• Where do I find the water heater in a mobile home?

• Does a tankless water heater in an attic require a drain pan? 

    Visit our WATER HEATERS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.