What is a good UEF rating for a tankless water heater?

For gas tankless units, 0.80-0.82 UEF is typical for a non-condensing model and 0.93-0.97 UEF is typical for a condensing model, per manufacturer spec sheets from Rinnai, Rheem, and Navien. For electric tankless units, UEF generally runs close to 0.99 since there's no exhaust heat loss to account for. ENERGY STAR cites 0.93 as an example UEF for a certified tankless gas or standard electric storage unit on its own explainer page, which gives a rough sense of where the certification bar sits, though the exact ENERGY STAR threshold varies by unit type and size.

Can I compare the UEF of a tankless water heater to a storage tank water heater?

Only if they were tested in the same DOE draw-pattern bin, and in practice this is a common mistake. UEF testing sorts water heaters into one of four usage bins based on expected daily hot water draw, and the DOE's own guidance is explicit that a unit rated 0.95 in one bin does not perform the same as a unit rated 0.95 in a different bin. A storage tank is often tested and rated to a lower-draw bin than its real-world use, while a tankless unit's continuous-flow design typically puts it in a higher bin. Comparing the two numbers side by side without checking the bin can make a tank look more efficient than it actually is in your home.

Why did my tankless water heater's UEF change from its old EF rating?

UEF replaced the older Energy Factor (EF) metric in 2017 under a revised DOE test procedure, and it's not a straight unit conversion — the two numbers were measured differently, so a model's published UEF and its predecessor's EF rating are not directly comparable even if it's the same basic unit. If you're comparing a water heater bought years ago against a new 2026 model, use UEF-to-UEF or EF-to-EF, not one against the other.

Where do I find the UEF rating for a specific tankless water heater model?

On the manufacturer's spec sheet or the yellow EnergyGuide label that ships with the unit — both list UEF directly. Our best tankless water heater guide and the individual brand roundups linked from it include the UEF figures we've verified against each manufacturer's own published specs, so you can compare models without digging through PDFs yourself.

What Does UEF Mean on a Tankless Water Heater? (2026 Guide)

Quick Answer: UEF (Uniform Energy Factor) is the U.S. Department of Energy's standardized efficiency rating for water heaters — a higher number means more of the energy you pay for goes into heating water instead of being lost as exhaust or standby heat. For tankless units, non-condensing gas models typically land around **0.80-0.82 UEF**, condensing gas models **0.93-0.97 UEF**, and electric tankless close to **0.99 UEF**, per manufacturer spec sheets. The catch most buyers miss: UEF ratings are only directly comparable within the same DOE draw-pattern usage bin, so a 0.95 next to a 0.95 on two different spec sheets isn't automatically an apples-to-apples tie.

Every tankless water heater spec sheet has a UEF number printed near the top, usually somewhere between 0.80 and 0.97. It looks like a simple efficiency percentage you can line up across models and pick the highest one. Mostly that works — but the rating has a wrinkle that trips up a lot of comparison shopping, and it’s worth understanding before you treat two UEF numbers as directly interchangeable.

Check the UEF on the spec sheet, not just the marketing headline

Manufacturer spec sheet or EnergyGuide label — both list the tested UEF directly

Condensing gas tankless units (PVC venting, secondary heat exchanger) post the highest UEF numbers in the category, typically 0.93 and up.
Non-condensing gas units (stainless venting) run lower, typically 0.80-0.82, but cost less upfront — see our condensing vs. non-condensing guide for the full trade-off.

What UEF actually measures

UEF stands for Uniform Energy Factor, the DOE’s standardized water-heater efficiency metric that replaced the older Energy Factor (EF) rating starting in 2017 under a revised test procedure. — ENERGY STAR It’s a ratio: how much of the energy a unit consumes actually ends up heating the water you use, versus what’s lost to exhaust gases, standby heat, or combustion inefficiency. A UEF of 0.93 means roughly 93% of input energy goes into heated water, with about 7% lost. — ENERGY STAR Because UEF replaced EF with a different test procedure rather than a simple rebranding, a unit’s old EF number and a newer model’s UEF number aren’t directly convertible — compare UEF to UEF, not across the two metrics.

The part almost nobody reads: usage bins

Here’s the detail that gets skipped on most spec-sheet comparisons. The DOE test sorts every water heater into one of four draw-pattern usage bins — generally described as Very Small, Low, Medium, and High — based on how much hot water a typical household in that bin draws per day, and a water heater’s UEF is only valid for comparison against another unit tested in the same bin. ENERGY STAR’s own guidance is direct about this: a higher UEF means a unit is more efficient than others in its own bin, and comparing across bins isn’t a fair comparison. — ENERGY STAR

Water heater type	Typical UEF range	Why
Electric tankless	~0.98-0.99	No combustion exhaust loss; nearly all input energy converts to heat
Condensing gas tankless	0.93-0.97	Secondary heat exchanger recovers exhaust heat before venting
Non-condensing gas tankless	0.80-0.82	Single heat exchanger; hotter, less-recovered exhaust
Gas storage tank	0.60-0.70	Standby heat loss from a stored, constantly-reheated tank of water
Heat pump water heater	3.0-4.1	Moves heat rather than generating it (not a 1:1 energy ratio, hence >1.0)

This is also why a heat pump water heater’s UEF of “3.5” isn’t a typo — it’s measuring heat moved per unit of electricity, not combustion efficiency, so it sits on a completely different scale than a gas unit’s UEF.

Why this matters for your actual comparison

In practice, a tankless water heater’s continuous-flow design tends to put it in a higher-draw bin than a storage tank sized for the same household, since the tankless unit’s rated capacity assumes it can keep serving fixtures indefinitely rather than until a tank runs dry. That means a tank’s UEF and a tankless unit’s UEF printed side by side on two spec sheets may not have been tested against the same daily-use assumption — the DOE’s own bin system exists specifically to prevent that exact side-by-side mistake. — ENERGY STAR The safest comparison is tankless-to-tankless, matched roughly by GPM class, which is also how our best tankless water heater guide and brand-by-brand roundups present the UEF figures we’ve verified.

By the numbers

0.93 — ENERGY STAR’s own example UEF for a certified tankless gas or standard electric storage water heater, cited on its official UEF explainer. — ENERGY STAR
0.63-0.95 — the typical UEF range across traditional (non-heat-pump) water heater types overall, per ENERGY STAR. — ENERGY STAR
3.3-4.1 — the typical UEF range for ENERGY STAR certified heat pump water heaters, which move 3-4 units of heat per unit of electricity consumed rather than generating heat directly. — ENERGY STAR
2017 — the year the DOE’s revised test procedure introduced UEF as the replacement for the older EF (Energy Factor) metric. — ENERGY STAR

The bottom line

UEF is a real, useful number for comparing tankless water heaters — but only once you know it’s bin-dependent, not a flat universal scale. Treat a non-condensing gas unit’s 0.81 and a condensing unit’s 0.95 as roughly accurate within the gas-tankless category, be skeptical of lining a tankless unit’s UEF up directly against a storage tank’s, and never compare a heat pump unit’s 3-point-something UEF against either — it’s measuring something fundamentally different. For how UEF factors into picking the right unit for your household size and climate, see our sizing guide, and for how the newest DOE efficiency rules affect commercial units specifically (a separate rating system from residential UEF), see our 2026 DOE regulations guide.