Tankless Water Heaters
Best Tankless Water Heater for House (2026): 3 Picks Compared
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For a whole house, the Rheem RTG Series leads this list: it delivers 7 GPM at a 35°F temperature rise with 160,000 BTU/hr output for 2-3 simultaneous showers. The ThermoMate CZ422NG offers up to 5 GPM at 102,000 BTU, and the EcoSmart ECO 8 is the electric pick at 8 kW.
Starting out? See the main guide: Best Tankless Water Heater
Top picks at a glance
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Best OverallRheem RTG Series 7.0 GPM Natural Gas9.8 View on Amazon -
9.7 View on Amazon -
Also GreatEcoSmart ECO 8 Tankless Water Heater9.2 View on Amazon
Compare the specs
Ranked on flow rate, power (kw), 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 | Power (kW) | Fuel | Temperature control | Weight | Warranty |
|---|---|---|---|---|---|---|
| 1. Rheem RTG Series 7.0 GPM Natural Gas | 7 GPM | — | Natural Gas | Yes | 46.5 lb | 1-year |
| 2. ThermoMate CZ422NG Natural Gas Tankless Water Heater | 5 GPM | — | Natural Gas | Yes | 22 lb | 3-year |
| 3. EcoSmart ECO 8 Tankless Water Heater | — | 8 kW | Electric | — | 4.75 lb | lifetime |
Rheem RTG Series 7.0 GPM Natural Gas
It delivers 7 GPM at a 35°F temperature rise with 160,000 BTU/hr output for 2-3 simultaneous showers.
- Flow rate: 7 GPM
- Fuel: Natural Gas
- Temperature control
- 1-year warranty stated
Good for
- Buyers who want hot water for 2-3 showers at once
- Owners of multi-bathroom homes who want continuous hot water
Skip it if
- You need a warranty longer than 1 year
- You want a flow rate above 7 GPM
It has a digital LED temperature control panel with ±1°F adjustments and a 0.82 UEF. It mounts on a wall indoors with a direct vent system and includes LeakGuard leak detection. It has built-in freeze protection and flame failure protection. It carries a 1-year warranty.
ThermoMate CZ422NG Natural Gas Tankless Water Heater
It delivers up to 5 GPM at 102,000 BTU with a 90–140°F adjustment range and a 3.5-inch LED display.
- Flow rate: 5 GPM
- Fuel: Natural Gas
- Temperature control
- 3-year warranty stated
Good for
- Buyers who want two showers running at the same time
- Buyers who want a 90 to 140°F adjustment range
Skip it if
- You need a flow rate above 5 GPM
- You want a warranty longer than 3 years
It holds temperature within ±1°F and adjusts from 90 to 140°F on a 3.5-inch LED display. It has an oxygen-free copper heat exchanger with up to 98% thermal efficiency and a 0.81 UEF. It measures 21 inches high by 13 inches wide by 7 inches deep with 3/4-inch water connections. It carries a 3-year warranty.
EcoSmart ECO 8 Tankless Water Heater
It provides 8 kW of electric heating in a 4.75 lb unit measuring 12 x 8 x 4.
- Power (kW): 8 kW
- Fuel: Electric
- Lifetime warranty stated
Good for
- Buyers who want a 4.75 lb electric unit
- Buyers who want a lifetime warranty on electronics
Skip it if
- You need more than 8 kW of power
- You need a natural gas unit
It runs on electricity at 8 kW with a 99.8% energy efficiency rating. It measures 12 x 8 x 4 and weighs 4.75 lb. It carries a lifetime warranty on electronics, the exchanger and the element.
How to choose
Match flow rate to simultaneous use
Flow rate in gallons per minute decides how many outlets run at once. The Rheem RTG Series delivers 7 GPM at a 35°F temperature rise for 2-3 simultaneous showers. The ThermoMate CZ422NG delivers up to 5 GPM for two showers at the same time. The EcoSmart ECO 8 is an 8 kW electric unit, so check its power against your household demand before choosing it.
Gas versus electric fuel
Fuel type shapes installation and supply. The Rheem RTG Series and the ThermoMate CZ422NG run on natural gas for indoor use. The EcoSmart ECO 8 runs on electricity at 8 kW. A gas unit needs a gas supply and a vent path, while an electric unit needs an electrical supply matched to its power.
Temperature control and adjustment
A temperature control holds output steady when demand changes. The Rheem RTG Series adjusts in ±1°F steps from a digital LED panel. The ThermoMate CZ422NG adjusts from 90 to 140°F on a 3.5-inch LED display and holds temperature within ±1°F. Set the temperature to the level your household needs and check the display for flow, fan and flame status.
FAQ
What flow rate do I need for a whole house?
Count the showers and outlets that run at the same time. The Rheem RTG Series delivers 7 GPM for 2-3 simultaneous showers, and the ThermoMate CZ422NG delivers up to 5 GPM for two showers at the same time.
Do these water heaters use gas or electricity?
The Rheem RTG Series and the ThermoMate CZ422NG run on natural gas. The EcoSmart ECO 8 runs on electricity at 8 kW.
What warranty does each pick carry?
The Rheem RTG Series carries a 1-year warranty. The ThermoMate CZ422NG carries a 3-year warranty. The EcoSmart ECO 8 carries a lifetime warranty on electronics, the exchanger and the element.
Can I adjust the water temperature?
The Rheem RTG Series adjusts in ±1°F steps from a digital LED panel. The ThermoMate CZ422NG adjusts from 90 to 140°F on a 3.5-inch LED display.
