Water heater sizing Last reviewed June 2026

Water Heater UEF Rating Explained: Energy Factor vs FHR Chart

By the WhatSize editorial team 4 min read Standards-reviewed

TL;DR

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.

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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%.

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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.