10 Best 40 Gallon Gas Water Heaters

After analyzing 79 products, scanning 395 reviews, spending more than 36 hours of research and speaking with our test users, we think the Takagi T-KJr2-IN-NG Indoor Tankless Water Heater is the one of the Best 40 Gallon Gas Water Heater on the market.

# Image Name Brand Price
1 Takagi T-KJr2-IN-NG Indoor Tankless Water Heater Takagi T-KJr2-IN-NG Indoor Tankless Water Heater, Natural Gas
(Editor’s Choice)
TAKAGI $$$$$ Check price
2 Rheem RTGH-95DVLN 9.5 GPM Indoor Direct Vent Tankless Natural Gas Rheem RTGH-95DVLN 9.5 GPM Indoor Direct Vent Tankless Natural Gas Water Heater Rheem $$$$$ Check price
3 Excel Pro Tankless Gas Water Heater NATURAL GAS 6.6 GPM Excel Pro Tankless Gas Water Heater NATURAL GAS 6.6 GPM Whole House and for Hydronic heating Compare to Rinnai, Rheem,Noritz, Bosch FREE FLUE KIT GASFLEX $$$$$ Check price
4 Eccotemp fvi12-NG FVI-12 Natural Gas Eccotemp fvi12-NG FVI-12 Natural Gas, 3.5 GPM, High Capacity Tankless Water Heater, White
(Best value for the money)
Eccotemp $$$$$ Check price
5 Takagi T-KJr2-OS-NG Outdoor Tankless Water Heater Takagi T-KJr2-OS-NG Outdoor Tankless Water Heater, Natural Gas TAKAGI $$$$$ Check price
6 Rinnai V65IN 6.6 GPM Indoor Low NOx Tankless Natural Gas Rinnai V65IN 6.6 GPM Indoor Low NOx Tankless Natural Gas Water Heater Rinnai $$$$$ Check price
7 Rheem RTG-84XLN 8.4 GPM Low NOx Outdoor Tankless Natural Gas Rheem RTG-84XLN 8.4 GPM Low NOx Outdoor Tankless Natural Gas Water Heater Rheem $$$$$ Check price
8 Eccotemp i12-NG Water Heater Eccotemp i12-NG Water Heater, 16 x 16 x 11 inches, Black Eccotemp $$$$$ Check price
9 Noritz EZTR40-NG Indoor Tankless Water Heater 6.6 GPM Natural Gas; Noritz EZTR40-NG Indoor Tankless Water Heater 6.6 GPM Natural Gas; Designed for Easy Replacement of 30/40-Gallon Tank Type Heaters Noritz $$$$$ Check price
10 VEVOR 18L Natural Gas Hot Water Heater 4.8GPM 36KW Tankless VEVOR 18L Natural Gas Hot Water Heater 4.8GPM 36KW Tankless Instant Boiler Stainless Steel Liquefied Natural Gas Water Heater with Shower Head Kit Wall-Mounted Water Heater (18L, Natural Gas) VEVOR $$$$$ Check price

Takagi T-KJr2-IN-NG Indoor Tankless Water Heater – Best Overall 40 Gallon Gas Water Heater

Takagi T-KJr2-IN-NG Indoor Tankless Water Heater
  • 140,000 BTU. Voltage: AC 120V
  • 6.6 GPM max flow rate. Water connection location- bottom
  • 4-Inch category III stainless steel venting required
  • Inlet, outlet thermistors for constant temperature monitoring
  • Energy factor of 0.81-0.83

Rheem RTGH-95DVLN 9.5 GPM Indoor Direct Vent Tankless Natural Gas

Rheem RTGH-95DVLN 9.5 GPM Indoor Direct Vent Tankless Natural Gas
  • 94-Percent Energy efficient with stainless-steel condensing heat exchanger
  • Intelligent electronic controls designed to increase energy efficiency and safety
  • Third party efficiency listed by AHRI
  • Up to 38-Feet of 3-Inch PVC Pipe or 5-Feet of 2-Inch PVC Pipe
  • Low Nox Version

Excel Pro Tankless Gas Water Heater NATURAL GAS 6.6 GPM

Excel Pro Tankless Gas Water Heater NATURAL GAS 6.6 GPM
  • Modulates heat output in response to the flow rate of water running through the unit.
  • Power vented directly vertically (rooftop) or sideways (wall) via Stainless Steel CAT III Flue 3.5" Diameter Included (20")
  • NATURAL GAS
  • Delivers 6.6 gpm of hot water with a 35°F Instant Temperature Rise
  • Certified for Installation in Manufactured (Mobile) Homes Pure Copper Heat Exchanger

Eccotemp fvi12-NG FVI-12 Natural Gas – Best Budget 40 Gallon Gas Water Heater

Eccotemp fvi12-NG FVI-12 Natural Gas
  • Whole home indoor, gas powered tankless water heater, rated at 3.6 GPM that activates only when in use, making it an energy saver.
  • For indoor installation with safe, efficient power ventilation and perfect for any small home, cabin or apartment.
  • Easy to read digital temperature display, on a compact and space-saving design with minimal noise output.
  • Safe electronic ignition system; plugs into standard 120v electrical outlet with UL-listed cord.
  • Uses standard 1/2" NPT water fittings and is equipped with easy to use manual water temperature controls.

Takagi T-KJr2-OS-NG Outdoor Tankless Water Heater

Takagi T-KJr2-OS-NG Outdoor Tankless Water Heater
  • Outside installation only; Includes internal freeze protection
  • 19,500 - 140,000 BTU/hr
  • 0.82 energy factor
  • 6.6 GPM max flow rate

Rinnai V65IN 6.6 GPM Indoor Low NOx Tankless Natural Gas

Rinnai V65IN 6.6 GPM Indoor Low NOx Tankless Natural Gas
  • Max BTU's 150,000
  • Max Energy Factor 0.82
  • Indoor Installations
  • Meets California and Texas NOx Emissions Standards
  • Lightweight and Compact

Rheem RTG-84XLN 8.4 GPM Low NOx Outdoor Tankless Natural Gas

Rheem RTG-84XLN 8.4 GPM Low NOx Outdoor Tankless Natural Gas
  • Natural Gas Tankless Water Heater
  • Outdoor
  • 8.4 gal/min. at 35-Degree Rise
  • UMC-117 remote control and 10-Feet of thermostat wire is included
  • Low Nox Version

Eccotemp i12-NG Water Heater

Eccotemp i12-NG Water Heater
  • Whole home indoor, gas powered tankless water heater, rated at 3 GPM that activates only on demand and no pilot light needed, reducing energy consumption
  • Sleek, modern design with black tempered glass front panel featuring an easy to use LED display controls
  • Features fully automatic temperature controls with an energy saving mode and child lock technology
  • Safe electronic ignition system; Plugs into standard 110v electrical outlet with UL-listed cord
  • Uses standard 1/2" NPT water fittings and comes with horizontal venting allowing for a convenient and quick installation

Noritz EZTR40-NG Indoor Tankless Water Heater 6.6 GPM Natural Gas;

Noritz EZTR40-NG Indoor Tankless Water Heater 6.6 GPM Natural Gas;
  • Endless hot water
  • Direct replacement for 30/40 gallon natural gas tank type water heater
  • High efficiency condensing technology.Capacity Range:0.5 - 6.6 GPM
  • Flexible Vent Kit Included
  • Isolation Valve Kit Included

VEVOR 18L Natural Gas Hot Water Heater 4.8GPM 36KW Tankless

VEVOR 18L Natural Gas Hot Water Heater 4.8GPM 36KW Tankless
  • Water Heater Material: Stainless Steel; Power Source: Natural Gas; Voltage: 1.5 volts; Wattage: 36KW; Installation Method: Wall-Mounted; Flow Rate: 4.8 GPM; Package Size: 27.6 x 15.7 x 8.3 inch; Gross weight: 18.96 lbs
  • NOTE!!! Every type of water heater is only suitable for one kind of gas. This 18L water heater is ONLY for Liquefied Natural Gas.
  • This hot water heater 18 L/min, 4.8gpm Natural Gas tankless water heater. The water heater gas pressure: 2800pa (about 0.4 psi)
  • Stainless steel panel. Over heat protection: Over 75 °C / 167℉ will automatically turn off; Over water pressure protection
  • 2 D Cell Battery Ignition; High efficient energy saving; Hot water heater LCD display shows clearly every degree change, gives users complete control of hot water

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