Updated October 2026 · 5 heaters, no paid placements

Best Gas Tankless Water Heaters in 2026

Natural gas from the street or propane from the tank: these five gas units are the ones we'd shortlist when one heater has to carry the house, indoor or outdoor. Ranked on buyer ratings, review volume and the specs each listing states, with the catch of each one spelled out.

See the ranking

In short

Our top pickMIZUDO 199,000 BTU Natural Gas Indoor9.2/10. The one we'd start with.$1,199 on Sep 30, 2026, may have changed

The 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 changed

The 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 where we'd start. The other four split between natural gas and propane, indoor and outdoor, so check your fuel line before you check the price. One slot per listing family: five different gas heaters, with the fuel printed on every card.

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

The ranking in detail

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

Stated maximum flow: 10.3 GPM
Stated gas input: 199,000 BTU/h
Natural gas, indoor mounting (listing)

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 ↗Read the reviewaffiliate link to Amazon.com

Gas tankless water heaters · Ranein · Runner-up

Ranein 190,000 BTU Natural Gas Indoor

7.9Very good · out of 10

Also available as: 130,000 BTU Propane Outdoor (5.3 GPM)

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

Stated maximum flow: 8.5 GPM
Stated gas input: 190,000 BTU/h
Natural gas, indoor mounting (listing)

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 ↗Read the reviewaffiliate link to Amazon.com

Gas tankless water heaters · Rinnai · Top 5 pick

Rinnai RU199iN Condensing

7.8Very good · out of 10

Best for: a busy house where two showers and the dishwasher overlap

Stated maximum flow: 11 GPM
Natural gas, indoor mounting (listing)

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

4.4/5 from buyers388 buyer reviewsSee current price ↗

See it on Amazon ↗Read the reviewaffiliate link to Amazon.com

Gas tankless water heaters · FOGATTI · Top 5 pick

FOGATTI Outdoor Propane Tankless

7.6Very good · out of 10

Best for: a mild-climate house with no easy vent route

Stated gas input: 120,000 BTU/h
Propane, outdoor mounting (listing)

The catch: Its 4.0/5 buyer rating is the lowest of these five.

4/5 from buyers166 buyer reviews$529.99 Price on Sep 30, 2026 · may have changed

See it on Amazon ↗Read the reviewaffiliate link to Amazon.com

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

Stated maximum flow: 8.4 GPM
Stated gas input: 157,000 BTU/h
Natural gas, indoor mounting (listing)

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 ↗Read the reviewaffiliate link to Amazon.com

Product images: Amazon listings

Best rated by fuel

The best-rated unit of this ranking for each fuel its listing states. Start from the fuel your house already has, then read across.

Natural gas	MIZUDO 199,000 BTU Natural Gas Indoor (#1) · 9.2/10 · 10.3 GPM, 199,000 BTU/h
Propane	FOGATTI Outdoor Propane Tankless (#4) · 7.6/10 · 120,000 BTU/h

How to choose

Match the fuel to the exact model. Natural gas and propane versions of one series share photos and most of the title. Read the fuel in the exact listing and in the model suffix, and keep that link for your gas fitter. A conversion is never something to assume.
Check the gas line against the stated BTU/h. A tankless burner is several times bigger than a tank burner. Your gas fitter checks that the line, the meter or the propane regulator can feed the stated input with every other gas appliance running.
Indoor or outdoor is a listing fact, not a choice. An indoor unit needs a vent route and combustion air; an outdoor unit needs a wall rated for it and a climate (or freeze protection) that suits it. Pick from the mounting the exact listing states.

Natural gas or propane: what changes

Of the 45 eligible listings, 32 run on natural gas and 13 on propane; 31 are indoor units and 14 are rated to hang outside. The fuel isn't a setting you pick later. Natural gas and propane versions of one series look identical in the photos, and the A. O. Smith guide we cite stresses specifying the correct fuel because the two burn differently. Read the fuel in the exact listing and in the model suffix, then hand that link to your gas fitter.

The burner size is the other surprise. The listings here state 80,000 to 199,900 BTU/h of input; PNNL's example tank burner is about 40,000 BTU, which is why a tankless swap often means a 3/4" gas line where a 1/2" one fed the tank. On propane, the regulator and the tank have to keep up as well. Outdoor propane units have their own best propane tankless water heaters ranking, the indoor natural gas units lead our best tankless water heaters list, and the natural gas vs propane guide covers the fuel question in plain words.

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 Gas Tankless Water Heaters in 2026

MIZUDO 199,000 BTU Natural Gas Indoor	MIZUDO	9.2	$1,199^†	Natural gas	10.3 GPM	199,000 BTU/h	120 V	Indoor	307
Ranein 190,000 BTU Natural Gas Indoor	Ranein	7.9	$699^†	Natural gas	8.5 GPM	190,000 BTU/h	Not stated	Indoor	710 (shared)^*
Rinnai RU199iN Condensing	Rinnai	7.8	See current price	Natural gas	11 GPM	Not stated	Not stated	Indoor, condensing	388
FOGATTI Outdoor Propane Tankless	FOGATTI	7.6	$529.99^†	Propane	Not stated	120,000 BTU/h	120 V	Outdoor	166
Rheem RTGH 8.4 GPM Natural Gas Indoor	Rheem	7.3	$1,168.99^†	Natural gas	8.4 GPM	157,000 BTU/h	Not stated	Indoor, condensing	60

^† 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.

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 gas tankless water heater in 2026?

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 45 complete gas tankless units whose exact listing states natural gas or propane, indoor or outdoor, 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.

Natural gas or propane tankless: which is better?

Neither, on paper. The right heater is the one built for the fuel you actually have. Natural gas usually means an indoor unit vented out a wall; all 13 propane listings here are outdoor models that hang near the tank. Propane is sold by the gallon and natural gas by the therm, so compare running costs with your own local prices.

How many BTU does a gas tankless water heater need?

Roughly GPM × temperature rise × 500, divided by the heater's efficiency. Two showers at 2.0 GPM each with 42 °F groundwater heated to 105 °F (a 63 °F rise) is about 126,000 BTU/h of heat, so about 154,000 BTU/h of input at 82 % efficiency. Our flow-rate calculator does the sum with your own fixtures.

Can a gas tankless water heater go outside?

Only if the exact model is rated for outdoor mounting. 14 of the eligible listings here state outdoor mounting; the indoor ones need a vent route and combustion air instead. PNNL notes that outdoor installation generally suits warm climates unless the unit and its pipes are freeze-protected.

How much does a gas tankless water heater cost?

Among the 40 eligible gas listings with a price we recorded, the box alone ran from $249.99 (APUS 80,000 BTU Natural Gas Indoor) to $1,815.58 (Noritz NR98SVNG Natural Gas), with a median of $824.50, on Sep 30, 2026. Prices move, and the installer's bill comes on top: gas line, venting and permit.

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 Tankless Water Heaters in 2026 →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 Whole-House Tankless Water Heaters in 2026: Gas and Electric →All rankings →Comparison tool →

Gas tankless water heaters →Rheem →Rinnai →Ranein →MIZUDO →Buying guides →