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Tankless vs Tank Water Heater Efficiency: UEF Ratings & Energy Savings 2026

The U.S. Department of Energy says tankless water heaters can be 24-34% more energy-efficient than conventional storage tanks in homes that use 41 gallons of hot water a day or less, and 8-14% more efficient in homes that use around 86 gallons. Here is what that means for your energy bill.

UEF Ratings by Water Heater Type

The Uniform Energy Factor (UEF) measures how efficiently a water heater converts energy into hot water. Higher is better. A UEF of 0.67 means 67 cents of every dollar becomes hot water; the rest is lost as waste heat.

TypeUEF RangeAnnual Energy CostNotes
Standard gas tank0.58-0.70$236-285/yrMost common, lowest upfront cost
Condensing gas tank0.80-0.95$174-207/yrENERGY STAR certified
Electric resistance tank0.90-0.95$593-626/yrEfficient conversion but electricity is costly per BTU
Gas tankless (non-condensing)0.82-0.88$188-201/yrGood efficiency, simpler venting
Gas tankless (condensing)0.90-0.97$170-184/yrBest gas efficiency, requires condensate drain
Electric tankless0.97-0.99$569-581/yrNear-perfect conversion efficiency
Heat pump (hybrid electric)2.0-4.5$125-282/yrMost efficient overall - moves heat rather than generating it

Annual cost at 55 gal/day (DOE medium draw, 58°F in, 125°F out) and the EIA 2025 US residential averages: $1.48 per therm (from $15.34 per Mcf) and 17.23 cents/kWh. Energy = gallons x 365 x 8.3 lb x 67°F / UEF.

Standby Heat Loss: The Hidden Energy Drain

A tank keeps 40-80 gallons of water hot at 120-140F continuously, regardless of use. The tank walls absorb that heat, requiring the burner to fire repeatedly to maintain temperature. This is standby loss.

Standby loss is already inside a tank's UEF: the DOE test runs for 24 hours, idle time included. That is why a minimum-efficiency gas tank rates 0.58 while a condensing tankless rates 0.93. Tankless units have zero standby loss.

Annual Savings: Switching to Gas Tankless

DOE draw patternGas Tank (0.58)Gas Tankless (0.93)Annual Saving10-Year Saving
Low (38 gal/day)$197/yr$123/yr$74/yr$741
Medium (55 gal/day)$285/yr$178/yr$107/yr$1,072
High (84 gal/day)$435/yr$271/yr$164/yr$1,637

Federal Tax Credit (25C) Expired After 2025

The One Big Beautiful Bill Act (P.L. 119-21) terminated the Section 25C Energy Efficient Home Improvement Credit. It applied only to equipment placed in service on or before 31 December 2025. For water heaters installed in 2026 there is no federal tax credit. The boxes below show what the credit covered while it was in force.

$600 (expired)
High-Efficiency Gas Tankless
  • Required UEF ≥ 0.82
  • Natural gas or propane fuel
  • Primary residence only
  • Was 30% of cost, capped at $600/year
  • Placed in service by 31 Dec 2025
$2,000 (expired)
Heat Pump Water Heater
  • Required UEF ≥ 2.0
  • Electric heat pump only
  • Primary residence
  • Was 30% of cost, capped at $2,000/year
  • Placed in service by 31 Dec 2025
What still helps in 2026: the federal credit is gone, but many state energy offices and electric utilities continue to offer rebates on heat pump water heaters - sometimes several hundred dollars. Check your utility and state energy office before buying. See our heat pump water heater guide for more.
Cost ComparisonHeat Pump GuideGas vs ElectricBest Brands 2026

Frequently Asked Questions

What is UEF rating and what is a good score?
UEF (Uniform Energy Factor) is the standard metric for water heater efficiency. It measures how much energy is converted into hot water vs lost. Standard gas tanks rate 0.58-0.70. A condensing gas tankless typically rates 0.82-0.97. Heat pump water heaters achieve 2.0-4.5 UEF, meaning they deliver 2-4.5 times more heat energy than the electricity they consume.
How much can I save by switching from a tank to a tankless water heater?
It follows from the two UEF ratings. At the DOE test's 55 gallons a day and the 2025 EIA average of $1.48 per therm, a condensing gas tankless (UEF 0.93) uses about $107 a year less gas than a minimum-efficiency 40-gallon gas tank (UEF 0.58). An electric tankless (0.96) against a minimum electric tank (0.92) saves about $26 a year at 17.23 cents/kWh, because electric tanks already convert most of their energy to hot water.
Is there a federal tax credit for a water heater in 2026?
No. The Section 25C Energy Efficient Home Improvement Credit was terminated by the One Big Beautiful Bill Act (P.L. 119-21) and applied only to equipment placed in service on or before 31 December 2025. Until then it covered up to $600 for qualifying gas tankless units (UEF >= 0.82) and up to $2,000 for heat pump water heaters, claimed on IRS Form 5695. For installations in 2026 there is no federal credit, but many state energy offices and electric utilities still offer rebates on heat pump water heaters, so check locally.
What is standby heat loss and why does it matter?
Standby heat loss is the energy a tank water heater uses keeping stored water hot around the clock, whether or not anyone draws it. It is already counted in a tank's UEF rating, which is measured over a 24-hour test that includes idle hours, so a tank's lower UEF is largely its standby loss. Tankless units have no tank and so no standby loss, which is the main reason their UEF is higher.

Updated 2026-11-10