Glossary · Hot water
UEF (uniform energy factor)
Also called: energy factor (EF)
A water heater's overall efficiency rating from a standard daily hot-water test; higher is better, and the best heat pump models score above 3.
What it means
UEF compares water heaters of the same type and draw pattern (how much hot water a household uses). Gas storage tanks score below 1, efficient gas tankless and condensing units approach 1, standard electric tanks are just under 1, and heat pump water heaters reach 3 to nearly 4. Older literature uses the energy factor (EF), which isn't directly comparable.
Why it matters in an audit
Comparing UEF lets you estimate operating costs between options and check rebate eligibility.
Typical numbers
Reference values with their sources. Your energy advisor’s report gives the figure for your own house.
| What | Value | Source |
|---|---|---|
| ENERGY STAR thresholds | Heat pump ≥ 3.30; gas storage ≥ 0.81 (medium draw, 20–55 gal) or ≥ 0.86 (high draw or over 55 gal); gas tankless ≥ 0.95 | energystar.gov ↗ |
| DOE FEMP comparison | Best heat pump model 3.93; standard electric tank 0.95 | energy.gov ↗ |
| NRCan (2012, older EF metric) | Conventional gas storage EF 0.53–0.70, average 0.62 | natural-resources.canada.ca ↗ |