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Updated October 2026 · 5 heaters, no paid placements

Best Tankless Water Heaters in 2026

Five indoor natural gas units we'd shortlist for the house where the tank runs cold by the third shower. Ranked on buyer ratings, review volume and the specs each listing states, with the catch of each one spelled out (outdoor propane and whole-house electric units have their own lists).

See the ranking Compare up to 3 water heaters

In short

MIZUDO 199,000 BTU Natural Gas IndoorOur top pickMIZUDO 199,000 BTU Natural Gas Indoor9.2/10. The one we'd start with.$1,199 on Sep 30, 2026, may have changedRanein 190,000 BTU Natural Gas IndoorThe crowd favouriteRanein 190,000 BTU Natural Gas Indoor710 buyer reviews (shared by its variants), 7.9/10. Plenty of owners to learn from.$699 on Sep 30, 2026, may have changedRinnai RU199iN CondensingThe most flow on paperRinnai RU199iN Condensing11 GPM per the listing, 7.8/10. The biggest figure among the rest.See current price

Short on time? The MIZUDO 199,000 BTU Natural Gas Indoor is the one we'd start with, and the other four are here in case your gas line, your vent route or your budget says otherwise. Variants that share one review pool take a single slot, so these are five different heaters, not one heater in five sizes.

Shopping by fuel or by feature? See the best gas tankless water heaters (natural gas and propane), the best electric tankless water heaters, the best propane tankless water heaters for an outside wall, the best high-efficiency tankless water heaters and the best whole-house tankless water heaters.

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

The ranking in detail

1MIZUDO 199,000 BTU Natural Gas Indoor
Gas tankless water heaters · MIZUDO · Top pick

MIZUDO 199,000 BTU Natural Gas Indoor

9.2Excellent · out of 10

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

  • Up to 10.3 GPM
  • ±1°F temperature control
  • Smart WiFi app control

The catch: Expect less than 10.3 GPM when the groundwater is cold.

4.4/5 from buyers307 buyer reviews$1,199 Price on Sep 30, 2026 · may have changed
See it on Amazon ↗ MIZUDO 199,000 BTU Natural Gas Indoor (opens in a new tab)Read the reviewaffiliate link to Amazon.com
2Ranein 190,000 BTU Natural Gas Indoor
Gas tankless water heaters · Ranein · Runner-up

Ranein 190,000 BTU Natural Gas Indoor

7.9Very good · out of 10

Best for: replacing a 40-gallon tank in a mid-size home

  • 190,000 BTU, 8.5 GPM
  • Serves 4-6 outlet points
  • Indoor natural gas unit

The catch: No ±1 °F temperature hold claimed for the Ranein, while most units here state one.

4.2/5 from buyers710 buyer reviews, shared by 2 variants$699 Price on Sep 30, 2026 · may have changed
See it on Amazon ↗ Ranein 190,000 BTU Natural Gas Indoor (opens in a new tab)Read the reviewaffiliate link to Amazon.com
4Rheem RTGH 8.4 GPM Natural Gas Indoor
Gas tankless water heaters · Rheem · Top 5 pick

Rheem RTGH 8.4 GPM Natural Gas Indoor

7.3Good · out of 10

Also available as: RTGH-95DVLN-3 Natural Gas Indoor (9.5 GPM) · RTGH 9.0 GPM Natural Gas Indoor (9 GPM)

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

  • 8.4 GPM, 157,000 BTU
  • 0.93 UEF condensing efficiency
  • 3-4 simultaneous showers

The catch: Only 60 buyer reviews so far, so that average can still move.

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
5Rheem RTG 9.5 GPM Natural Gas Indoor
Gas tankless water heaters · Rheem · Top 5 pick

Rheem RTG 9.5 GPM Natural Gas Indoor

7.2Good · out of 10

Also available as: RTG 7.0 GPM Natural Gas Indoor (7 GPM)

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

  • 9.5 GPM, 199,900 BTU
  • 0.82 UEF efficiency
  • Digital LED temperature control

The catch: Its 4.2/5 buyer rating ties for the lowest of these five.

4.2/5 from buyers88 buyer reviews$1,047.92 Price on Sep 30, 2026 · may have changed
See it on Amazon ↗ Rheem RTG 9.5 GPM Natural Gas Indoor (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 GPMRanein 190,000 BTU Natural Gas Indoor (#2) · 7.9/10 · 8.5 GPM
9 GPM or moreMIZUDO 199,000 BTU Natural Gas Indoor (#1) · 9.2/10 · 10.3 GPM

How to choose

How to pick a tankless water heater

Fuel first, because it decides everything else. If you have natural gas and a wall the vent can go through, start with the list above. With propane and an outside wall, go to the outdoor propane ranking. With no gas at all, the whole-house electric ranking is your list, after a chat with your electrician about the panel.

Then size for January, not for the box. Count the fixtures that run together on a busy morning, subtract your winter inlet temperature from the shower temperature you want, and read the maker's chart at that rise. Our flow-rate calculator does the arithmetic, and the tankless water heater buying guide walks through the rest. Last, price the install: the installation cost guide lists the line items that often cost more than the heater.

Tankless water heater pros and cons

The good: no stored tank to run dry (the limit becomes flow, not volume), no heat lost from a tank sitting idle, and a longer life. The PNNL guide written for the DOE Building America program puts tankless energy costs 5 to 40 % below a tank on the same fuel, and service life at up to 20 years against 10 to 15 for a tank.

The catch: PNNL also puts the installed cost at 1.5 to 2 times a tank heater, mostly because of the gas line, the vent or the electrical service. Flow drops when the groundwater is cold, some units won't fire for a trickle at the sink, and hard water means descaling. The full comparison is in our tankless water heater pros and cons guide.

Which tankless water heater brand is best?

We rate listings, not logos, so there's no brand trophy here. What the data does show: Rheem (23 complete heaters), Rinnai (22 complete heaters) and Ranein (10 complete heaters) have the most rated units in our catalogue, and the #1 picks of our three main rankings are the MIZUDO 199,000 BTU Natural Gas Indoor (9.2/10), FOGATTI Outdoor Propane Tankless (9.1/10) and Rheem 18 kW Electric, 240V (9.3/10). Every maker with three or more products has its own page in our tankless water heater brands index.

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 Tankless Water Heaters in 2026
MIZUDO 199,000 BTU Natural Gas IndoorMIZUDO9.2$1,199†Natural gas10.3 GPM199,000 BTU/h120 VIndoor307
Ranein 190,000 BTU Natural Gas IndoorRanein7.9$699†Natural gas8.5 GPM190,000 BTU/hNot statedIndoor710 (shared)*
Rinnai RU199iN CondensingRinnai7.8See 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
Rheem RTG 9.5 GPM Natural Gas IndoorRheem7.2$1,047.92†Natural gas9.5 GPM199,900 BTU/hNot statedIndoor88

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

* Shared: the same review pool appears on every variant of a listing family (Ranein, 2 variants), so the count is not specific to one variant.

Our 2026 rankings

Every ranking on the site, with its #1 pick and the number of models ranked.

All rankings →
Rinnai RU199iN Condensing#1: Rinnai RU199iN Condensing · 9.1/10Best High-Efficiency Condensing Tankless Water Heaters in 20265 models rankedRheem 18 kW Electric, 240V#1: Rheem 18 kW Electric, 240V · 9.3/10Best Whole-House Electric Tankless Water Heaters in 20265 models rankedFOGATTI Outdoor Propane Tankless#1: FOGATTI Outdoor Propane Tankless · 9.1/10Best Outdoor Propane Tankless Water Heaters in 20265 models rankedMIZUDO 199,000 BTU Natural Gas Indoor#1: MIZUDO 199,000 BTU Natural Gas Indoor · 9.2/10Best Whole-House Tankless Water Heaters in 2026: Gas and Electric5 models rankedMIZUDO 199,000 BTU Natural Gas Indoor#1: MIZUDO 199,000 BTU Natural Gas Indoor · 9.2/10Best Gas Tankless Water Heaters in 20265 models ranked

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 tankless water heater in 2026?

For an indoor natural gas install, our pick is the MIZUDO 199,000 BTU Natural Gas Indoor, at 9.2/10 (excellent). It has 307 buyer reviews averaging 4.4/5, and its listing states 10.3 GPM and 199,000 BTU/h. Next in line: the Ranein 190,000 BTU Natural Gas Indoor at 7.9/10.

How is this ranking built?

We start from 32 complete natural gas tankless units whose exact listing states indoor (or indoor and outdoor) mounting, 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 higher GPM always better?

Not on its own. A listing usually quotes its maximum flow at a gentle temperature rise, and the usable flow falls when the incoming water is cold. In this ranking, the listings that state a maximum flow give 8.4 GPM to 11 GPM. Size from the flow you need at your winter rise; our flow-rate calculator does that arithmetic.

Does an indoor gas tankless heater need special venting?

Yes. An indoor gas unit needs a vent route, combustion air and a gas line sized for its input, as the maker and your local code set them. In this ranking, two of the five listings state a condensing design, which also makes condensate that has to drain somewhere. A licensed plumber or gas fitter decides all of this; we give no installation instructions.

Are tankless water heaters worth it?

Usually, when your household runs the tank out and your house can take the install (the pros and cons above carry the PNNL figures). A like-for-like tank swap can still be the cheaper move when the gas line, the vent or the panel would need major work, so price both before you decide.

Gas or electric tankless: which should I buy?

Gas makes more hot water per unit; electric needs no vent but a lot of amps. If you already have gas, start with this ranking or the gas tankless ranking; if not, start with the electric tankless ranking and your electrician. Our gas vs electric guide compares the two on equal terms.

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.

Tankless flow-rate calculator →Buying guide: how to choose a tankless water heater →Best Outdoor Propane Tankless Water Heaters in 2026 →Best Whole-House Electric Tankless Water Heaters in 2026 →Best High-Efficiency Condensing Tankless Water Heaters in 2026 →Best Gas Tankless Water Heaters in 2026 →Best Whole-House Tankless Water Heaters in 2026: Gas and Electric →All rankings →Comparison tool →
Gas tankless water heaters →Rheem →Rinnai →Ranein →MIZUDO →Buying guides →