Water heater sizing Last reviewed June 30, 2026
Water Heater UEF Rating Explained: Energy Factor vs FHR Chart
By the WhatSize editorial team 4 min read Standards-reviewed
UEF (Uniform Energy Factor) measures water heater efficiency from 0.50 to 4.0+. Higher UEF = lower operating cost. Gas tanks: UEF 0.60-0.70. Electric tanks: UEF 0.90-0.95. Heat pump: UEF 3.0-4.0. Gas tankless: UEF 0.82-0.96. FHR (First Hour Rating) is separate — it measures capacity, not efficiency.
What the UEF Rating Actually Tells You
The Uniform Energy Factor (UEF) replaced the Energy Factor (EF) standard in 2015 under DOE 10 CFR 430. It measures how efficiently a water heater converts energy into hot water — higher UEF means more of your energy bill goes to heating water and less is lost as standby heat.
UEF is not a direct savings calculator. A jump from 0.60 to 0.95 UEF on an electric tank saves roughly $100-150/year depending on local energy costs. The real savings come from switching from a gas tank (UEF 0.62) to a heat pump (UEF 3.5+), which can cut water heating costs by 60-70%.
Top picks for this size
These Amazon-available picks meet the calculated spec. For region-specific or licensed contractor-installed options, consult a local professional. See our Disclaimers.
UEF Rating Range by Water Heater Type
- Gas storage tank (30-75 gal): UEF 0.60-0.70 — lowest efficiency, most common type
- Electric storage tank (30-80 gal): UEF 0.90-0.95 — better than gas, higher operating cost
- Gas tankless: UEF 0.82-0.96 — 15-30% more efficient than gas tank
- Electric tankless: UEF 0.94-0.99 — efficient but high electrical demand
- Heat pump (hybrid): UEF 3.0-4.0 — highest efficiency, 3-4x better than electric tank
Frequently asked questions
What is a good UEF rating for a water heater?
For gas tanks, UEF 0.65+ is good. For electric tanks, UEF 0.92+ is good. For maximum savings, a heat pump water heater with UEF 3.5+ pays for itself in 2-4 years versus a standard electric tank.
Is a higher UEF rating worth the extra cost?
Calculate payback: yearly savings = (old UEF - new UEF) x annual energy cost. A heat pump ($1,800) vs standard electric ($600) = $1,200 premium. At $150/year savings, payback is 8 years. If you stay 10+ years, it's worth it.
Does UEF affect First Hour Rating (FHR)?
No — UEF and FHR measure different things. UEF is efficiency (how much energy converts to heat), FHR is capacity (how many gallons of hot water in the first hour). Choose by FHR first, then UEF for operating cost.
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- What Size Water Heater for a 3-4 Person Household?
- What Size Water Heater for a Family of 5?
- Tank vs Tankless Water Heater: Which Size Is Right?
- What Size Water Heater for Electric vs Gas Homes?
- Water Heater FHR Chart: First Hour Rating by Household Size
- Tankless Water Heater GPM Chart by Household Size
- What Size Water Heater for a 2-Bathroom House?
- 40 vs 50 Gallon Water Heater: Which Size Do You Need?
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