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Updated October 2026 · 5 heaters, no paid placements

Best High-Efficiency Condensing Tankless Water Heaters in 2026

Five condensing gas units: the kind with a second heat exchanger that pulls heat out of the exhaust before it leaves the house. If you're swapping an old tank and want the efficient option, this is the shortlist we'd start from. Ranked on buyer ratings, review volume and what each listing states.

See the ranking

In short

Rinnai RU199iN CondensingOur top pickRinnai RU199iN Condensing9.1/10. The one we'd start with.See current priceRinnai RX160iN Condensing Smart SenseThe crowd favouriteRinnai RX160iN Condensing Smart Sense70 buyer reviews, 6.8/10. Plenty of owners to learn from.$1,442.70 on Sep 30, 2026, may have changedRheem RTGH 8.4 GPM Natural Gas IndoorThe best stated UEFRheem RTGH 8.4 GPM Natural Gas IndoorUEF 0.93 per the listing, 7.3/10. The biggest figure among the rest.$1,168.99 on Sep 30, 2026, may have changed

Want the efficient one without reading five spec sheets? Start with the Rinnai RU199iN Condensing. The other four differ on flow, burner size and what the box costs before the vent pipe and the condensate drain. Variants of one listing share a slot, so these are five different condensing heaters, not one heater in five sizes.

Written from each listing's specs and buyer reviews, not from our own use · How we rate

The ranking in detail

2Rheem RTGH 8.4 GPM Natural Gas Indoor
Gas tankless water heaters · Rheem · Runner-up

Rheem RTGH 8.4 GPM Natural Gas Indoor

7.3Good · out of 10

Also available as: RTGH 9.0 GPM Natural Gas Indoor (9 GPM)

Best for: a two-bathroom house with one shower running at a time

  • Stated maximum flow: 8.4 GPM
  • UEF 0.93 stated in the listing
  • Stated gas input: 157,000 BTU/h

The catch: 60 buyer reviews is still a thin record; the average can shift.

4.4/5 from buyers60 buyer reviews$1,168.99 Price on Sep 30, 2026 · may have changed
See it on Amazon ↗ Rheem RTGH 8.4 GPM Natural Gas Indoor (opens in a new tab)Read the reviewaffiliate link to Amazon.com
3Rinnai RX160iN Condensing Smart Sense
Gas tankless water heaters · Rinnai · Top 5 pick

Rinnai RX160iN Condensing Smart Sense

6.8Good · out of 10

Also available as: RX130iN Condensing Smart Sense (7.1 GPM) · RXP160iN Condensing Smart Sense (9 GPM)

Best for: a family that showers back to back before school

  • Stated maximum flow: 9 GPM
  • UEF 0.97 stated in the listing
  • Condensing design stated in the title

The catch: Venting and a gas line sized for its input come on top of the price.

4.2/5 from buyers70 buyer reviews$1,442.70 Price on Sep 30, 2026 · may have changed
See it on Amazon ↗ Rinnai RX160iN Condensing Smart Sense (opens in a new tab)Read the reviewaffiliate link to Amazon.com
5Rheem Prestige Condensing Natural Gas
Gas tankless water heaters · Rheem · Top 5 pick

Rheem Prestige Condensing Natural Gas

4.4Fair · out of 10

Best for: swapping a 50-gallon tank for a house with three bathrooms

  • Stated maximum flow: 11 GPM
  • Condensing design stated in the title

The catch: Its 3.3/5 buyer rating is the lowest of these five.

3.3/5 from buyers27 buyer reviews$1,199.99 Price on Sep 30, 2026 · may have changed
See it on Amazon ↗ Rheem Prestige Condensing Natural Gas (opens in a new tab)Read the reviewaffiliate link to Amazon.com

Product images: Amazon listings

Best rated by stated maximum flow

The best-rated unit for each band of maximum flow its listing states. Count the showers that run together on a busy morning, then read across (and keep in mind that the listing figure is a mild-weather one).

6 to 8.9 GPMRheem RTGH 8.4 GPM Natural Gas Indoor (#2) · 7.3/10 · 8.4 GPM
9 GPM or moreRinnai RU199iN Condensing (#1) · 9.1/10 · 11 GPM

How to choose

What "high efficiency" means on these listings

Plenty of gas tankless listings put "high efficiency" in the title, non-condensing ones included. We only let a heater in here when its listing title states a condensing design, because that's the part that actually changes the efficiency (and the install). Ten listings with a buyer review record pass that bar, from seven listing families. Where a listing states its Uniform Energy Factor, the figures run from 0.93 to 0.97. For scale, the PNNL guide written for the DOE Building America program gives energy factors of 0.82 to 0.94 for gas tankless units and 0.57 to 0.70 for gas tank heaters.

Honestly, the catch is the install. A condensing unit vents through PVC or stainless pipe and makes slightly acidic condensate, which has to drain somewhere, ideally through a neutralizer (PNNL recommends one). If your old tank sits mid-basement with a metal flue up the chimney, price that work before you fall for a UEF. The condensing vs non-condensing guide weighs the trade, the gas tankless ranking has the non-condensing alternatives, and the condensate neutralizer kits we rate sit in the parts collection.

Comparison table

All 5 on one screen. Tap a column header to sort by what matters at 6:45 on a weekday: flow, power or price.

Comparison table: Best High-Efficiency Condensing Tankless Water Heaters in 2026
Rinnai RU199iN CondensingRinnai9.1See current priceNatural gas11 GPMNot statedNot statedIndoor, condensing388
Rheem RTGH 8.4 GPM Natural Gas IndoorRheem7.3$1,168.99†Natural gas8.4 GPM157,000 BTU/hNot statedIndoor, condensing60
Rinnai RX160iN Condensing Smart SenseRinnai6.8$1,442.70†Natural gas9 GPMNot statedNot statedIndoor, condensing70
Takagi T-H3S-DV-N Condensing IndoorTakagi4.5See current priceNatural gas8 GPMNot statedNot statedIndoor, condensing25
Rheem Prestige Condensing Natural GasRheem4.4$1,199.99†Natural gas11 GPMNot statedNot statedIndoor, condensing27

† Prices as of Sep 30, 2026; they may have changed. The button always shows today's price.

How we rank

Every heater gets a score out of 10 from its exact listing. We look at what buyers give it, how many of them there are, and how completely the seller documents the specs and the warranty, then at how it stacks up against the other heaters in the list. On an exact tie, the listing slug settles the order.

We haven't installed or run these heaters ourselves, and a commission never moves a rating or a rank.

Read the methodology →Affiliate disclosure
  • 45 % buyer rating, damped when a listing has fewer than 50 reviews.
  • 35 % review volume, on a logarithmic scale up to 5,000 reviews.
  • 20 % documentation: feature bullets, images and stated brand of the listing.
  • Flow, BTU/h input, kW and voltage show up only when the exact listing states them. A headline GPM is not your winter flow, and we measure nothing ourselves.
  • One slot per listing family: variants of one parent listing, which usually share one review pool, count once and are listed under the best-rated variant.
  • Prices carry the date we recorded them. They may have changed since; the button shows today's offer.

Frequently asked questions

Which is the best high-efficiency tankless water heater in 2026?

Our pick is the Rinnai RU199iN Condensing, at 9.1/10 (excellent). It has 388 buyer reviews averaging 4.4/5, and its listing states 11 GPM. Next in line: the Rheem RTGH 8.4 GPM Natural Gas Indoor at 7.3/10.

How is this ranking built?

We start from 10 complete gas tankless units whose exact listing title states a condensing design, each with a buyer review record. Each one gets a rating out of 10: 45 % buyer rating, 35 % review volume and 20 % how completely the listing documents its specs. Variants of one listing family (same parent listing) share a single slot, so you see 5 different heaters rather than one heater in 5 sizes.

Is a condensing tankless water heater worth it?

It depends on how much hot water you use and what the install costs in your house. A condensing unit sends less heat up the vent, which pays back fastest in a busy household; it also needs a condensate drain and its own vent run, which can eat the saving in a small one. Ask for two written quotes for the same flow, one condensing and one non-condensing, and compare them line by line.

What UEF do these high-efficiency heaters state?

Five of the ten eligible listings state a Uniform Energy Factor, from 0.93 to 0.97. The others don't print one in the listing, so we don't guess. Compare a UEF only with models in the same usage bin (the bins are set by maximum GPM, as our tankless vs tank guide explains).

Do condensing tankless water heaters need special venting?

They vent differently from a tank. The PNNL guide notes that high-efficiency units use PVC or stainless steel vent pipe, and that the slightly acidic condensate has to be drained per local code, with a neutralizer recommended. A licensed installer sets the route from the exact manual; we give no venting instructions.

What does a high-efficiency tankless water heater cost?

Among the 8 eligible condensing listings with a price we recorded, the box alone ran from $499 (Vancepic Condensing Natural Gas Indoor) to $1,685.60 (Rinnai RXP160iN Condensing Smart Sense), with a median of $1,242.10, on Sep 30, 2026. Prices move, and the installer's bill comes on top, including the vent and the condensate drain.

Are the prices up to date?

Each price is the one we recorded on Sep 30, 2026, and it may have changed since. The button always opens the exact listing with today's price and seller.

Have you installed these water heaters yourselves?

No, we haven't installed them in a house of our own. The ratings come from what buyers say and from the specs stated in each exact listing, weighed with a formula we publish.

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