First Hour Rating (FHR)
The First Hour Rating (FHR) measures how much hot water a storage water heater can deliver in the first hour of use, starting with a full tank. It combines tank capacity and recovery rate, making it a key sizing metric for household peak demand. Tankless units do not use FHR; they are rated by flow rate at a specific temperature rise.
💡 Key Takeaways
- ✓The First Hour Rating (FHR) measures how much hot water a storage water heater can deliver in the first hour of use, starting with a full tank. It combines tank capacity and recovery rate, making it a key sizing metric for household peak demand. Tankless units do not use FHR; they are rated by flow rate at a specific temperature rise.
- ✓FHR applies to storage water heaters, not tankless models.
- ✓Higher FHR often means higher input or larger tank size.
- ✓Sizing to demand avoids energy waste and hot water shortages.
First Hour Rating (FHR)
/fɜrst aʊər ˈreɪtɪŋ (FHR)/
Definition
The First Hour Rating (FHR) measures how much hot water a storage water heater can deliver in the first hour of use, starting with a full tank. It combines tank capacity and recovery rate, making it a key sizing metric for household peak demand. Tankless units do not use FHR; they are rated by flow rate at a specific temperature rise.
What does First Hour Rating tell you?
It tells you how many gallons of hot water a tank water heater can supply in the first hour of use.
Source: The Cooling Company
Quick Facts
How First Hour Rating (FHR) Works
FHR combines tank size and recovery speed.
Real-World Application
A family of four chooses a water heater with an FHR that supports back-to-back showers and morning laundry without running out of hot water.
Pro Tip
Estimate your peak hour hot water demand and choose an FHR that meets or slightly exceeds it.
“Estimate your peak hour hot water demand and choose an FHR that meets or slightly exceeds it.”
Important Things to Keep in Mind
- FHR applies to storage water heaters, not tankless models.
- Higher FHR often means higher input or larger tank size.
- Sizing to demand avoids energy waste and hot water shortages.
Did You Know?
FHR provides a more practical sizing guide than tank size alone because it includes recovery rate.
FAQ
How do I estimate my peak hour demand?
Add up hot water use for showers, laundry, and dishes during your busiest hour.
Is a higher FHR always better?
Only if it matches your demand. Oversizing can increase standby losses.
Do heat pump water heaters have an FHR?
Yes. Storage-type heat pump models list FHR values on the label.
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