Tankless Water Heaters
Best Natural Gas Whole House Tankless Water Heater (2026): 5 Picks Compared
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For a whole house on natural gas, the Ranein leads this list: it covers 3-5 water points at 5.3 GPM and 130,000 BTU in a compact indoor wall-mount unit. If you need more flow, the Rheem reaches 9.0 GPM at a 35°F rise.
Starting out? See the main guide: Best Tankless Water Heater
Top picks at a glance
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Best OverallRanein Natural Gas Tankless Water Heater9.8 View on Amazon -
9.7 View on Amazon -
Highest Flow RateRheem RTGH Series 9.0 GPM Natural Gas9.4 View on Amazon -
9.3 View on Amazon -
9.2 View on Amazon
Compare the specs
Ranked on flow rate, temperature 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 | Weight | Warranty |
|---|---|---|---|---|---|
| 1. Ranein Natural Gas Tankless Water Heater | 5.3 GPM | Natural Gas | — | 38 lb | 2-year |
| 2. FOGATTI Tankless Water Heater Natural Gas Indoor | 7.5 GPM | Natural Gas | Yes | — | — |
| 3. Rheem RTGH Series 9.0 GPM Natural Gas | 9 GPM | Natural Gas | Yes | 59.88 lb | 1-year |
| 4. MIZUDO 120,000 BTU Natural Gas Tankless Water | 5.1 GPM | Natural Gas | Yes | — | 2-year |
| 5. Westinghouse Gas Tankless Water Heater Outdoor | 8.1 GPM | — | Yes | 42 lb | 2-year |
Ranein Natural Gas Tankless Water Heater
It pairs 5.3 GPM with 130,000 BTU for 3-5 water points in a compact indoor wall-mount unit.
- Flow rate: 5.3 GPM
- Fuel: Natural Gas
- 2-year warranty stated
Good for
- Households needing hot water at 3-5 water points
- Buyers who want a compact indoor wall-mount unit
Skip it if
- You need more than 5.3 GPM of flow
- You live above 2,000 feet in altitude
It measures 23.15 inches long, 14.17 inches wide and 6.30 inches deep, and weighs 38 lb. It uses 1/2-inch NPT water inlet fittings and a 3/4-inch gas inlet, with a blower placed underneath. It carries a 2-year warranty, and the maker advises draining it through the pressure relief valve if it sits unused in cold weather.
FOGATTI Tankless Water Heater Natural Gas Indoor
It adds 7.5 GPM and 170,000 BTU with water servo control holding temperature within ±1°F.
- Flow rate: 7.5 GPM
- Fuel: Natural Gas
- Temperature control
Good for
- Households running 3-5 outlet points at once
- Buyers who want servo temperature control within ±1°F
Skip it if
- You need more than 7.5 GPM of flow
- You live above 2,000 feet in altitude
It measures 25 by 16.3 by 7.3 inches and works with low water pressure from 15 to 150 PSI. It uses a copper heat exchanger and a 304 stainless steel burner, with a four-stage combustion system and CSA certification. It carries 2 years of full coverage and 5 years of coverage for the heat exchanger.
Rheem RTGH Series 9.0 GPM Natural Gas
Its 9.0 GPM at a 35°F rise and 180,000 BTU/hr output give this list its highest flow rate.
- Flow rate: 9 GPM, the highest here
- Fuel: Natural Gas
- Temperature control
- 1-year warranty stated
Good for
- Large households needing 3-4 simultaneous showers
- Buyers who want condensing efficiency at 0.93 UEF
Skip it if
- You need more than 9.0 GPM of flow
- You plan to install it yourself
It delivers 9.0 GPM at a 35°F rise with 180,000 BTU/hr and a 0.93 Uniform Energy Factor. It has digital LED temperature control with precision ±1°F, built-in freeze protection, and it is CSA certified. It weighs 59.88 lb and carries a 15-year heat exchanger warranty with 5-year parts coverage.
MIZUDO 120,000 BTU Natural Gas Tankless Water
It adds WiFi and app control to 5.1 GPM and 120,000 BTU, with indoor or outdoor installation.
- Flow rate: 5.1 GPM
- Fuel: Natural Gas
- Temperature control
- 2-year warranty stated
Good for
- Buyers who want WiFi and app control from anywhere
- Households needing 2-4 outlet points with flexible installation
Skip it if
- You need more than 5.1 GPM of flow
- You want outdoor use without buying a conversion kit
It delivers 5.1 GPM at 120,000 BTU with temperature held within 1°F during simultaneous multi-fixture use. It has WiFi and app control for temperature settings, energy monitoring and maintenance notifications. It uses a phosphorous-deoxidized copper heat exchanger and a stainless steel combustion chamber, and it carries a 2-year full unit warranty with 5-year heat exchanger coverage.
Westinghouse Gas Tankless Water Heater Outdoor
It delivers 8.1 GPM and 180,000 BTU outdoors for 3-5 fixtures, with temperature held within ±1°F.
- Flow rate: 8.1 GPM
- Temperature control
- 2-year warranty stated
Good for
- Households needing 3-5 fixtures outdoors
- Buyers who want a 95–158°F temperature range
Skip it if
- You need an indoor installation
- You need more than 8.1 GPM of flow
It delivers up to 8.1 GPM at 180,000 BTU for 3-5 fixtures, with temperature held within ±1°F. It is built for outdoor installation with freeze protection and a variable-speed combustion fan, and it is CSA certified. It weighs 42 lb, uses standard 3/4-inch NPT plumbing and carries a 2-year limited warranty with 5-year heat exchanger coverage.
How to choose
Flow rate decides how many fixtures run
Flow rate, measured in gallons per minute, sets how much hot water the unit can supply at once. A household running two showers and a dishwasher at the same time needs more gallons per minute than a household running one shower. In this list the Rheem reaches 9.0 GPM at a 35°F rise, the Westinghouse reaches 8.1 GPM, the FOGATTI reaches 7.5 GPM, the Ranein reaches 5.3 GPM and the MIZUDO reaches 5.1 GPM. Match the figure to the number of fixtures your household runs together.
Temperature stability and controls
Temperature stability is how steady the output stays when another tap opens. The FOGATTI, MIZUDO and Westinghouse hold output within ±1°F. The Rheem uses digital LED temperature control with precision ±1°F. The MIZUDO adds WiFi and app control for temperature settings, energy monitoring and maintenance notifications.
Indoor, outdoor and venting
Tankless units need a vent path for exhaust, and the right one depends on where the unit sits. The Ranein, FOGATTI and Rheem install indoors, the Westinghouse is built for outdoor installation, and the MIZUDO converts from indoor to outdoor with accessory kits that must be purchased. The MIZUDO indoor setup requires a 3-inch OD vent pipe system. Check the vent parts your install needs before ordering.
FAQ
What flow rate do I need for a whole house?
Count the fixtures your household runs at once. The Rheem reaches 9.0 GPM, the Westinghouse 8.1 GPM, the FOGATTI 7.5 GPM, the Ranein 5.3 GPM and the MIZUDO 5.1 GPM.
Can these heaters run several showers at once?
The Ranein and FOGATTI cover 3-5 water points, the Westinghouse covers 3-5 fixtures, the Rheem suits 3-4 simultaneous showers and the MIZUDO covers 2-4 outlet points.
Which of these installs outdoors?
The Westinghouse is built for outdoor installation. The MIZUDO converts from indoor to outdoor with accessory kits that must be purchased, while the Ranein, FOGATTI and Rheem install indoors.
Do any of these offer app control?
The MIZUDO offers WiFi and app control for temperature settings, energy monitoring and maintenance notifications.
