UEF (Uniform Energy Factor) is the U.S. Department of Energy efficiency rating for residential water heaters, measuring how much of the energy a unit consumes ends up as delivered hot water during a standardized day of use. It replaced the older Energy Factor (EF) in 2017, and a higher UEF means less energy for the same hot water.
Why it matters to you
UEF lets you compare models on the yellow EnergyGuide label: a 0.95 UEF unit delivers the same hot water as a 0.65 UEF unit with about 32% less energy input (1 − 0.65/0.95). Compare UEF only between water heaters of the same fuel type and usage bin.
Practical guidance
Read UEF together with the first-hour rating for tanks or the maximum gallons per minute for tankless units, because an efficient heater that cannot meet your household's demand is the wrong heater. Check the label's usage bin, such as medium or high, before comparing two models.
Typical UEF ranges by water heater type
| Water heater type | Typical UEF range | How it heats |
|---|---|---|
| Gas storage tank (standard) | About 0.58–0.70 | Burner under a stored tank; flue carries heat away |
| Gas tankless (non-condensing) | About 0.81–0.87 | Heats on demand; no standby loss |
| Gas tankless (condensing) | About 0.90–0.97 | Also recovers heat from exhaust gases |
| Electric resistance tank | About 0.90–0.95 | Elements heat stored water |
| Heat pump water heater | About 3.0–4.0 | Moves heat from surrounding air into the tank |
What is a good UEF rating for a water heater?
It depends on the fuel and type. Standard gas tanks typically rate around 0.58 to 0.70, gas tankless units around 0.81 to 0.97, and electric resistance tanks around 0.90 to 0.95. Heat pump water heaters rate above 3.0 because they move heat rather than create it, so compare a model against others of the same type.
Why can a heat pump water heater have a UEF above 1?
A heat pump water heater uses electricity to move heat from the surrounding air into the water instead of generating heat directly. It can therefore deliver more heat energy than the electricity it consumes, which the UEF shows as a number above 1.0.
What are UEF usage bins?
DOE tests each water heater under one of four draw patterns, called very small, low, medium, and high, chosen from the unit's first-hour rating or maximum flow. A UEF is only directly comparable between models tested in the same bin, which is listed on the label and spec sheet.
Is UEF the same as the old Energy Factor?
No. UEF comes from an updated DOE test procedure meant to better reflect real household use. A UEF number is not directly comparable to an older EF number printed on a legacy unit's label or spec sheet.