Tankless Water Heaters
Best Natural Gas Tankless Hot Water Heater (2026): Top 4 by the Specs
As an Amazon Associate I earn from qualifying purchases. Specs below come from each product's Amazon listing; we do not test products in person.
The Rheem RTG Series leads this list as Best Overall: 9.5 GPM at a 35°F temperature rise covers 3-4 simultaneous showers, with a digital LED temperature control panel and precision ±1°F adjustments. If flow matters most, the Rinnai RXP199iN reaches 11.1 GPM for 7 fixtures at once, while the Ranein covers 4-6 outlet points at 42 lb.
Starting out? See the main guide: Best Tankless Water Heater
Top picks at a glance
-
Best OverallRheem RTG Series 9.5 GPM Natural Gas9.8 View on Amazon -
Highest Flow RateRinnai RXP199iN Condensing Smart Sense Tankless Water9.4 View on Amazon -
Lightest PickRanein Natural Gas Tankless Water Heater9.2 View on Amazon -
Also GreatMIZUDO Natural Gas Tankless Water Heater9.2 View on Amazon
Compare the specs
Ranked on flow rate, temperature control, phone app control from each listing, plus how many buyers have rated it. A dash (—) means we could not confirm that figure from the listing.
| Pick | Flow rate | Fuel | Temperature control | Phone app control | Weight | Warranty |
|---|---|---|---|---|---|---|
| 1. Rheem RTG Series 9.5 GPM Natural Gas | 9.5 GPM | natural gas | Yes | — | 46.5 lb | 1-year |
| 2. Rinnai RXP199iN Condensing Smart Sense Tankless Water | 11.1 GPM | propane or natural gas | — | — | 58 lb | 1-year |
| 3. Ranein Natural Gas Tankless Water Heater | 8.5 GPM | natural gas | — | — | 42 lb | 2-year |
| 4. MIZUDO Natural Gas Tankless Water Heater | 10.3 GPM | natural gas | Yes | Yes | 55.5 lb | 2-year |
Rheem RTG Series 9.5 GPM Natural Gas
It covers whole-house use at 9.5 GPM for 3-4 simultaneous showers, with a digital LED temperature control panel and CSA certification.
- Flow rate: 9.5 GPM
- Fuel: natural gas
- Temperature control
- 1-year warranty stated
Good for
- Owners of multi-bathroom homes with 3-4 water points running
- Buyers who want digital LED temperature control with ±1°F adjustments
Skip it if
- You need more than 9.5 GPM of flow
- You want a warranty longer than 1 year
It delivers 199,900 BTU/hr output with a 0.82 Uniform Energy Factor (UEF) and a direct vent system for indoor installation. It has freeze protection and flame failure protection, plus a wall-mount design. Mounting hardware and a detailed installation manual are included, and professional installation is required.
Rinnai RXP199iN Condensing Smart Sense Tankless Water
It reaches up to 11.1 GPM for 7 fixtures at once, with Smart-Circ recirculation and an internal pump.
- Flow rate: 11.1 GPM, the highest here
- Fuel: propane or natural gas
- 1-year warranty stated
Good for
- Buyers who run 7 fixtures at once
- Owners who want indoor or outdoor installation
Skip it if
- You need more than 11.1 GPM of flow
- You want a warranty longer than 1 year
It runs on propane or natural gas through a Smart Sense gas control system, and it installs indoors or outdoors with a Versa Vent. An internal pump with Smart-Circ technology schedules recirculation around water usage patterns. It has a Quick Flush feature and an easy-to-use interface, a UEF of .98, and an RX-OVC vent cap is required for outdoor install.
Ranein Natural Gas Tankless Water Heater
It weighs 42 lb and covers 4-6 outlet points at up to 8.5 GPM, with a wall-mount design.
- Flow rate: 8.5 GPM
- Fuel: natural gas
- 2-year warranty stated
- 42 lb, the lightest here
Good for
- Buyers who want a 42 lb wall-mount unit
- Owners with 4-6 outlet points to serve
Skip it if
- You need more than 8.5 GPM of flow
- You want a warranty longer than 2 years
It has 190,000 BTU of heating capacity and measures 24.25 inches long, 15.08 inches wide and 8.07 inches high. A blower under the unit adjusts speed with wind pressure and water temperature. It uses 3/4 inch G water inlet fittings, carries a 2-year warranty, and needs its pressure relief valve opened to drain remaining water after long cold-weather disuse.
MIZUDO Natural Gas Tankless Water Heater
It pairs 10.3 GPM with WiFi and app control, ±1°F temperature control and a 107°F default setting.
- Flow rate: 10.3 GPM
- Fuel: natural gas
- Temperature control
- Phone app control
- 2-year warranty stated
Good for
- Buyers who want app control from anywhere
- Owners with 2-3 bathrooms plus kitchen and laundry
Skip it if
- You need more than 10.3 GPM of flow
- You want a warranty longer than 2 years
It has 199,000 BTU of heating input and a 0.53 GPM low-flow activation level. Temperature adjusts up to 149°F from a 107°F default, and the LED display pairs with app control and instant abnormal alerts. It is CSA certified for indoor installation, with a sealed concentric direct-vent system and a 3 inch by 5 inch concentric vent kit.
How to choose
Compare flow rate at a stated rise
Flow rate alone does not tell the whole story: the Rheem gives 9.5 GPM at a 35°F temperature rise, while the Rinnai reaches 11.1 GPM for 7 fixtures at once. Compare the flow figure with the number of showers and fixtures you run at once: the Rheem covers 3-4 simultaneous showers, the Ranein covers 4-6 outlet points, and the MIZUDO covers 2-3 bathrooms plus kitchen and laundry. A higher flow figure suits more simultaneous use.
Temperature control and app control
App control means managing the unit from a phone: only the MIZUDO offers it here, with operating status, temperature fine-tuning and instant abnormal alerts through its app. The Rinnai mentions a WiFi control module that is not included, so do not count it as app control.
Venting, installation and upkeep
The Rheem and the MIZUDO are indoor units with direct vent systems, and the Rinnai also installs outdoors with a Versa Vent and an RX-OVC vent cap for outdoor install. Professional installation is required for the Rheem and recommended for the Rinnai and the MIZUDO. For upkeep, the Rinnai has a Quick Flush feature for simplified flushing, and the Ranein needs its pressure relief valve opened to drain remaining water after long cold-weather disuse.
FAQ
What flow rate do I need for simultaneous showers?
Match the flow figure to the fixtures you run at once. The Rheem covers 3-4 simultaneous showers at 9.5 GPM, the Rinnai reaches 11.1 GPM for 7 fixtures at once, and the Ranein covers 4-6 outlet points.
Which of these water heaters has app control?
Only the MIZUDO offers app control: you can manage it from anywhere via its app, check operating status, fine-tune temperature and get instant abnormal alerts. The Rinnai mentions a WiFi control module that is not included.
Do these tankless water heaters need professional installation?
Professional installation is required for the Rheem and recommended for the Rinnai and the MIZUDO.
What warranty terms do these water heaters carry?
The Rheem and the Rinnai carry a 1-year warranty, while the Ranein and the MIZUDO carry a 2-year warranty. The Rheem also gives a 15-year heat exchanger warranty and a 5-year parts warranty, and the MIZUDO gives 5-year heat exchanger coverage.
