Tankless Water Heaters
Best Indoor Tankless Water Heater (2026): 5 Models Side by Side
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.
For indoor endless hot water, the MIZUDO leads this list with 10.3 GPM, 199,000 BTU of heating input, app control and temperature control within ±1°F. The five picks cover indoor whole-house installs on propane or natural gas, with flow rates from 7.5 GPM to 10.3 GPM.
Starting out? See the main guide: Best Tankless Water Heater
Top picks at a glance
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Best OverallMIZUDO Propane Gas Tankless Water Heater9.8 View on Amazon -
9.6 View on Amazon -
9.6 View on Amazon -
9.5 View on Amazon -
Also GreatRheem RTGH Series 8.4 GPM Natural Gas9.2 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. MIZUDO Propane Gas Tankless Water Heater | 10.3 GPM | Propane | Yes | Yes | 55.5 lb | 2-year |
| 2. Rinnai RE199iN Non-Condensing Natural Gas Tankless Water | 9.8 GPM | Natural Gas | — | — | 52.1 lb | — |
| 3. FOGATTI Tankless Water Heater Natural Gas Indoor | 7.5 GPM | Natural Gas | Yes | — | — | — |
| 4. Westinghouse Tankless Water Heater Gas Indoor | 7.9 GPM | Natural Gas | Yes | Yes | 39.3 lb | 2-year |
| 5. Rheem RTGH Series 8.4 GPM Natural Gas | 8.4 GPM | Natural Gas | Yes | — | 59.88 lb | 1-year |
MIZUDO Propane Gas Tankless Water Heater
It delivers 10.3 GPM with 199,000 BTU of heating input, app control and temperature control within ±1°F.
- Flow rate: 10.3 GPM, the highest here
- Fuel: Propane
- Temperature control
- Phone app control
- 2-year warranty stated
Good for
- Propane households that need 10.3 GPM across 2 to 3 bathrooms
- Buyers who want app control and Alexa voice control
Skip it if
- You need natural gas instead of propane
- Your home sits above 3,000 feet in elevation
It heats water only when needed, with a 0.53 GPM low-flow activation for faucets and showers. The temperature adjusts from 95 to 149°F with a default 107°F daily comfort setting, and the sealed concentric direct-vent system draws outdoor air for combustion. It measures 24.8 by 15.9 by 10.4 inches, uses 3/4 inch NPT connections, and carries a 2-year full unit warranty with 5-year heat exchanger coverage.
Rinnai RE199iN Non-Condensing Natural Gas Tankless Water
It delivers 9.8 GPM with 199,000 BTU of heating input for multiple fixtures at once, on natural gas.
- Flow rate: 9.8 GPM
- Fuel: Natural Gas
Good for
- Natural gas households that need 9.8 GPM for multiple fixtures
- Buyers who want an LED display with diagnostic codes
Skip it if
- You need propane instead of natural gas
- You need more than 9.8 GPM of flow
It heats water only when needed, with a compact, space-saving wall-mounted design. The LED display shows diagnostic codes and service reminders. It supports showers, laundry and dishwasher use, and carries a 15-year limited warranty on the heat exchanger.
FOGATTI Tankless Water Heater Natural Gas Indoor
It delivers 7.5 GPM with 170,000 BTU and water servo control within ±1°F for 3 to 5 outlet points.
- Flow rate: 7.5 GPM
- Fuel: Natural Gas
- Temperature control
Good for
- Natural gas households running 3 to 5 outlet points
- Buyers who want water servo temperature control
Skip it if
- You need more than 7.5 GPM of flow
- Your home sits above 2000 feet in elevation
It uses a high-efficiency copper heat exchanger with a 304 stainless steel burner and a four-stage combustion system. The compact design measures 25 by 16.3 by 7.3 inches and works with low water pressure from 15 to 150 PSI. An active heating anti-freeze device is built in.
Westinghouse Tankless Water Heater Gas Indoor
It delivers 7.9 GPM with 180,000 BTU, built-in WiFi app control and temperature stability within ±1°F.
- Flow rate: 7.9 GPM
- Fuel: Natural Gas
- Temperature control
- Phone app control
- 2-year warranty stated
Good for
- Natural gas households that want app and voice control
- Buyers who need hot water at 0.53 GPM low flow
Skip it if
- You need more than 7.9 GPM of flow
- You need propane instead of natural gas
It supplies hot water to 3 showers at once, with a minimum activation flow of 0.53 GPM and operation at water pressure as low as 15 PSI. Temperature adjusts from 95 to 149°F, and the app adjusts temperature, monitors operating status and sends fault alerts. It carries a 2-year limited warranty for the complete unit with a 5-year warranty for the heat exchanger.
Rheem RTGH Series 8.4 GPM Natural Gas
It delivers 8.4 GPM at a 35°F rise with 157,000 BTU/hr and digital LED temperature control within ±1°F.
- Flow rate: 8.4 GPM
- Fuel: Natural Gas
- Temperature control
- 1-year warranty stated
Good for
- Natural gas households that need 8.4 GPM for 3 to 4 showers
- Buyers who want condensing technology with 0.93 UEF
Skip it if
- You need more than 8.4 GPM of flow
- You need propane instead of natural gas
It uses condensing technology with a 0.93 Uniform Energy Factor and ultra-low NOx emissions. The digital LED temperature control holds precision within ±1°F, and built-in freeze protection is included. It is CSA certified. Mounting hardware and an installation manual are included.
How to choose
Match flow rate to simultaneous use
Flow rate in gallons per minute decides how many showers, faucets and appliances run at once without a drop in hot water. The MIZUDO lists 10.3 GPM, the Rinnai 9.8 GPM, the Rheem 8.4 GPM, the Westinghouse 7.9 GPM and the FOGATTI 7.5 GPM. Count the showers and fixtures that run together in your home, then pick a flow rate that covers that total. A higher flow rate suits more simultaneous use; a lower one suits fewer fixtures at once.
Fuel first, then controls
Fuel decides the shortlist: the MIZUDO runs on propane, while the Rinnai, FOGATTI, Westinghouse and Rheem run on natural gas. The MIZUDO and Westinghouse offer app control with WiFi. The FOGATTI uses water servo technology. The Rheem uses a digital LED temperature control. Pick the fuel your home already has, then pick the control style you will use every day.
Check venting, space and altitude
Indoor tankless heaters need proper venting and professional installation, which the MIZUDO, Rinnai and Rheem recommend. Measure the install space against the unit size: the MIZUDO measures 24.8 by 15.9 by 10.4 inches and the FOGATTI measures 25 by 16.3 by 7.3 inches. Altitude matters too: the MIZUDO is not recommended above 3,000 feet, and the FOGATTI is recommended below 2000 feet. Confirm venting, space and altitude before ordering.
FAQ
What flow rate do I need for a whole house?
Add up the showers and fixtures that run at the same time, then match that total to a flow rate here, from 7.5 GPM on the FOGATTI to 10.3 GPM on the MIZUDO.
Do these water heaters need professional installation?
The MIZUDO, Rinnai and Rheem recommend professional installation, and the Rinnai adds proper venting and code compliance for gas line connection.
Which of these heaters work with an app?
The MIZUDO and the Westinghouse offer app control with WiFi, and the Westinghouse also answers to voice control.
What does temperature control within ±1°F mean?
It means the heater adjusts gas and water flow to hold the set temperature steady, instead of swinging hot and cold. The MIZUDO, FOGATTI, Westinghouse and Rheem all hold temperature within ±1°F.
