Space Heaters
Best Natural Gas Tankless Heater (2026): Our 5 Picks Ranked
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 a large home, the Ranein leads this list: it pairs 8.5 GPM with 190,000 BTU for 4-6 outlet points, and the Rheem and Rinnai follow with 9.5 and 9.8 GPM for multi-fixture use. If your home runs two showers at once, the ThermoMate covers that need at 5 GPM, and the Westinghouse covers 2-4 fixtures at 5.1 GPM.
Starting out? See the main guide: Best Space Heater
Top picks at a glance
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Best OverallRanein Natural Gas Tankless Water Heater9.8 View on Amazon -
Runner-UpRheem RTG Series 9.5 GPM Natural Gas9.7 View on Amazon -
9.6 View on Amazon -
9.6 View on Amazon -
9.2 View on Amazon
Compare the specs
Ranked on 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 | Phone app control | Weight | Warranty |
|---|---|---|---|
| 1. Ranein Natural Gas Tankless Water Heater | — | 42 lb | 2-year |
| 2. Rheem RTG Series 9.5 GPM Natural Gas | — | 46.5 lb | 1-year |
| 3. ThermoMate CZ422NG Natural Gas Tankless Water Heater | — | 22 lb | 3-year |
| 4. Rinnai RE199iN Non-Condensing Natural Gas Tankless Water | — | 52.1 lb | — |
| 5. Westinghouse Indoor Natural Gas Tankless Water Heater | Yes | — | — |
Ranein Natural Gas Tankless Water Heater
It pairs 8.5 GPM with 190,000 BTU for 4-6 outlet points, with an LED display and a wall-mount design.
- 2-year warranty stated
Good for
- Homes that run 4-6 outlet points at once
- Buyers who want endless hot water without a 30-minute preheat wait
Skip it if
- Your home sits above 2,000 feet in elevation
- You need more than 8.5 GPM at peak demand
It measures 24.25 inches long, 15.08 inches wide and 8.07 inches high, weighs 42 lb and uses standard 3/4-inch G water inlet fittings. A blower underneath adjusts its speed with outside wind pressure and water temperature. In cold weather after a long period without use, the pressure relief valve drains the water left inside. It carries a 2-year warranty.
Rheem RTG Series 9.5 GPM Natural Gas
It delivers 9.5 GPM at a 35-degree temperature rise with 199,900 BTU per hour for 3-4 simultaneous showers.
- 1-year warranty stated
Good for
- Large households that run 3-4 showers at once
- Buyers who want a digital LED panel with 1-degree adjustments
Skip it if
- You need more than 9.5 GPM at peak demand
- You want a condensing model instead of a non-condensing one
It is a non-condensing indoor unit with a direct vent system and a 0.82 Uniform Energy Factor. The digital LED panel adjusts temperature in 1-degree steps, and the unit has freeze protection, flame failure protection and multi-point protection. Mounting hardware and an installation manual come in the box. The heat exchanger carries a 15-year warranty and parts carry 5 years. It is CSA-certified.
ThermoMate CZ422NG Natural Gas Tankless Water Heater
It holds up to 5 GPM at 102,000 BTU for two showers at once, with a 3.5-inch LED display and 90 to 140-degree adjustment.
- 3-year warranty stated
Good for
- Homes that run two showers at the same time
- Buyers who want a 3.5-inch LED display with error codes
Skip it if
- You need more than 5 GPM at peak demand
- You want temperature adjustment outside 90 to 140 degrees
It measures 21 inches high, 13 inches wide and 7 inches deep, weighs 22 lb and uses standard 3/4-inch NPT water connections with a 1/2-inch NPT gas inlet. It has boil-dry, freeze, flame-out, overheat, timeout, pipe blockage, high-temperature lock and excessive air pressure protections. It carries a 3-year warranty.
Rinnai RE199iN Non-Condensing Natural Gas Tankless Water
It delivers up to 9.8 GPM at 199,000 BTU for multiple fixtures at once, with an LED display and diagnostic codes.
Good for
- Large households that run showers, laundry and a dishwasher together
- Buyers who want service reminders on an LED display
Skip it if
- You need more than 9.8 GPM at peak demand
- You want a condensing model instead of a non-condensing one
It is a non-condensing indoor unit that heats water only when needed, with a wall-mounted design and an LED display that shows diagnostic codes and service reminders. It supports multiple fixtures at once, including showers, laundry and a dishwasher. The heat exchanger carries a 15-year limited warranty and parts carry 5 years.
Westinghouse Indoor Natural Gas Tankless Water Heater
It pairs up to 5.1 GPM with 120,000 BTU for 2-4 fixtures, with WiFi app control and 1-degree temperature stability.
- Phone app control
Good for
- Homes that run 2-4 fixtures at the same time
- Buyers who want to adjust temperature from a phone app
Skip it if
- You need more than 5.1 GPM at peak demand
- You want temperature adjustment outside 95 to 149 degrees
It supports 2-4 fixtures at once, including showers, sinks, dishwashers and laundry appliances. The phone app and LED panel adjust water temperature and show daily water usage reports with real-time temperature visibility. Self-modulating technology adjusts gas and water flow to hold temperature within 1 degree, adjustable from 95 to 149 degrees. It is CSA-certified and has freeze protection and a variable-speed combustion fan.
How to choose
Match GPM to simultaneous fixtures
A GPM figure states how much hot water the unit can deliver per minute. Compare it with how many fixtures run at once in your home: the Ranein covers 4-6 outlet points at 8.5 GPM, the Rheem covers 3-4 simultaneous showers at 9.5 GPM, the Rinnai covers multiple fixtures at up to 9.8 GPM, the ThermoMate covers two showers at up to 5 GPM, and the Westinghouse covers 2-4 fixtures at up to 5.1 GPM. Pick a figure that covers your peak use, not just one fixture.
Read BTU with temperature rise
BTU states the heating capacity of the unit, and temperature rise is the difference between incoming cold water and the hot water you want. The Rheem gives 9.5 GPM at a 35-degree temperature rise with 199,900 BTU per hour, while the ThermoMate holds a stable 105 degrees from a 65-degree inlet. A colder inlet means the same unit delivers less flow at your target temperature, so check both figures together.
Controls, venting and upkeep
Every pick here is an indoor unit, and the Rheem uses a direct vent system while the Rinnai and Rheem call for professional installation. In freezing weather, drain a unit left unused for a long period: the Ranein drains through its pressure relief valve, and the Westinghouse drains fully, and follow the manual for venting and gas connections.
FAQ
What size natural gas tankless heater do I need?
Match GPM and outlet points to your peak use: the Ranein covers 4-6 outlet points at 8.5 GPM, the Rheem covers 3-4 showers at 9.5 GPM, and the ThermoMate covers two showers at up to 5 GPM.
Do these heaters need professional installation?
The Rheem requires professional installation, and the Rinnai recommends a qualified technician for gas line connection and venting. All five picks are indoor units, so venting and gas connections must meet local codes.
Can I control a tankless heater from my phone?
The Westinghouse adjusts temperature and shows daily water usage reports through a phone app. The Rheem and ThermoMate adjust temperature from an LED panel or display.
What does UEF mean on a tankless heater?
UEF stands for Uniform Energy Factor, a rating of how efficiently the unit turns fuel into hot water. The Rheem carries a 0.82 UEF and the ThermoMate carries a 0.81 UEF.
