UEF: How Efficient It Is
UEF (Uniform Energy Factor) is the official efficiency rating for water heaters. Higher is better. A standard electric tank is usually around 0.9 to 0.95. The heat pump water heaters we reviewed all list 3.75, because the heat pump moves heat from the air instead of making it.
In practice, a higher UEF means lower running costs for the same hot water. Your real savings depend on your hot water use, electricity price and where the tank sits.
First-Hour Rating: How Much Hot Water at Once
The first-hour rating (FHR) is how many gallons of hot water the tank can deliver in one busy hour, starting full. It matters more than tank size for back-to-back showers.
- Rinnai REHP50: 73 gallons, per the listing.
- Senville 50 gallon: 69 gallons, per the listing.
How to Use Them
- Estimate your busiest hour: showers, laundry and dishwasher together.
- Pick a tank with an FHR at or just above that.
- Then compare UEF to see which costs less to run.
For tank sizes, see our size guide.
Want to see how a heat pump water heater fits with the rest of your home? Our Whole-Home Energy Calculator adds up what a thermostat, an EV charger, a backup battery and more would mean for your monthly bill.