The short answer
UEF is the Uniform Energy Factor, the measure of a water heater's overall efficiency under the federal test procedure. Higher is better. ENERGY STAR's draft Version 5.0 criteria ask for a UEF of at least 0.95 for gas instantaneous (tankless) water heaters and at least 3.30 for integrated heat pump water heaters (2.20 for 120-volt models).
Typical values
| Type | UEF threshold |
|---|---|
| Gas instantaneous (tankless) | 0.95 |
| Integrated heat pump | 3.30 |
| 120 V heat pump / split system | 2.20 |
| Gas storage, high draw | 0.86 |
On our pages
Where a listing states a UEF, it appears in the spec grid; we don't estimate one.
Products mentioned
Questions readers ask
Is a higher UEF better?
Yes: more of the energy that goes in comes out as hot water. Compare UEF within the same type and draw pattern.