Best natural gas tankless water heaters – A Buyer’s Guide
The pattern is always predictably the same. Standing “au naturel” in the shower, you’re staying just out of reach of the cold water. A tremble runs down your spine as you wait for the hot water. That’s quite enough, thank you. Tired of an ailing hot water system, an oldster that’s fitted with a slowpoke of a tank, you’ve made your choice. You’ve decided to actively research tankless water heaters.
From the off, the benefits are plain to see. Tankless hot water arrives instantly at your faucets and shower heads. Furthermore, these appliances are also known as on-demand heating systems, which means your shower will work its therapeutic magic when the need arises, not at all times of the day and night. In plain English, these technologically advanced appliances save money, yet they have more to offer than your old tank type water heater.
- GPM – The Gallons Per Minute flow rate helps you to gauge the number of showers the appliance will simultaneously supply with hot water. Mid-range GPM ratings won’t heat more than two showers at a time. Furthermore, that figure drops if you live in a cold region.
- NG – Natural gas, a cheap fuel source. Note, fuel affordability can fluctuate. The energy tariffs are higher in areas where electricity is popular. Still, even when electricity is the popular energy source, natural gas appliances tend to heat water faster. Balance these facts when you’re debating fuel issues.
- BTU – An acronym that stands for British Thermal Units. It determines the amount of gas energy burned. Use this figure to assess heater efficiency.
- Energy Star Compliance – A certification that lends authority to the BTU and flow rate factors. It also takes account of the Energy factor rating.
- Energy Factor – Tankless water heaters use a number of calculations to determine how efficiently they perform. The energy factor number expresses those complex formulas as a simple to interpret figure. The closer that number comes to one, the more efficient the heating system becomes.
Outdoor natural gas
tankless water heater Indoor natural gas
tankless water heater
Shot Descriptions
- Takagi T-KJr2-IN-NG Indoor Tankless Water Heater – The Best Budget All-Arounder
- Rinnai V65IN 6.6 GPM Indoor Low NOx Tankless Water Heater – The Best Low Emission Budget Appliance
- Rheem RTG-84XLN 8.4 GPM Low NOx Outdoor Tankless Water Heater – The Best Low-Emission Outdoor Model
- Takagi T-KJr2-OS-NG Outdoor Tankless Water Heater – Best Budget Outdoor Water Heater
- Takagi T-H3-DV-N Condensing High-Efficiency Natural Gas Indoor Tankless Water Heater – Best Large Home Appliance
- Rinnai RUC98iN Ultra Series Natural Gas Tankless Water Heater – Best Concentric or PVC venting option
- Rinnai RL75iN Natural Gas Tankless Water Heater – Best digital controller model
- Noritz NR981-SV-NG Indoor-Outdoor Tankless Water Heater – The Best in Venting Versatility
- Bosch Greentherm C1050ES NG Tankless Water Heater – Best Feature Rich Water Heater
- Noritz EZTR40-NG Indoor Tankless Water Heater – Best Affordable Condensing System
Quick Comparison Table
Item model | Size, Weight, Usage | Max flow | Warranty |
---|---|---|---|
Takagi T-KJr2-IN-NG![]() Check the price | 6.7" x 13.8" x 20.3", 38 lbs, Indoor | 6.6 GPM | 10 year heat exchanger and 5 year parts |
Rinnai V65IN 6.6 GPM![]() Check the price | 13.9 x 8.8" x 23.6", 49.8 lbs, Indoor | 6.5 GPM | No data |
Rheem RTG-84XLN![]() Check the price | 14" x 10" x 26", 54 lbs, Outdoor | 8.4 GPM | No data |
Takagi T-KJr2-OS-NG![]() Check the price | 6.7" x 13.8" x 20.5", 38 lbs, Outdoor | 6.6 GPM | Residential: 12 year heat exchanger, 5 year parts and 1 year labor |
Takagi T-H3-DV-N![]() Check the price | 11.2" x 17.8" x 24.9", 59 lbs, Indoor | 10 GPM | No data |
Rinnai RUC98iN![]() Check the price | 10" x 18.5" x 26", 82 lbs, Indoor | 9.8 GPM | 12 year heat exchanger and 5 year parts |
Rinnai RL75iN![]() Check the price | 14" x 9.3" x 23" 65.9 lbs, Indoor | 7.5 GPM | 12-Year Warranty on Heat Exchanger, 5 Year Parts |
Noritz NR981-SV-NG![]() Check the price | 17" x 13" x 29", 54 lbs, Indoor-Outdoor | 9.8 GPM | No data |
Bosch Greentherm C1050ES NG ![]() Check the price | 11.2" x 17.9" x 30.5" 86 lbs, Indoor | 10.5 GPM | 3 - 15 Years depending on application |
Noritz EZTR40-NG![]() Check the price | 27.2" x 18.3" x 9.4" 86 lbs, Indoor | 6.6 GPM | 12 years heat exchanger, 5 years parts, 1 year labor |
Indoor natural gas tankless water heater
Takagi T-KJr2-IN-NG Indoor Tankless Water Heater, Natural Gas
Gas-fired, this is the smallest model in the Takagi range. The output rating promises a 150,000-BTU energy output and a 6.6-GPM max flow rate, which is enough to supply on-demand heated water to one, maybe two bathrooms or showers. Reliable by design, this model isn’t a suitable fit for larger homes.
The review opens with a budget-friendly low tariff tankless hot water heater. Purchase this model if you live in a small home or apartment, knowing it’s recommended as a built-to-last appliance. In point of fact, that last feature is supported by a 15-year warranty.
Pros and Cons
- Fueled by Natural Gas (NG)
- Energy factor of 0.81 to 0.83
- Affordable
- Friendly customer service department
- 140,000-BTU, 6.6-GPM heated output
- Requires 4-inch stainless steel venting
- Not designed for larger properties

Again, it’s compact, but that’s a common feature among tankless water heaters. This time around, the 150,000-BTU energy output and 6.6-GPM capacity suggest you’ll get the best out of this gas-fueled model if you install it in a mid-sized property, not a large family home. Aimed at small families, the Rinnai V65IN is a high-performance device.
Still in budget-friendly territory, this is a feature-rich gas waterless heater. Output and capacity ratings are satisfactorily high, then there’s an enhanced scale detection system, a temperature lock, and a leak detection function to tempt your itchy fingers to dip into your wallet.
Pros and Cons
- Natural Gas fueled
- Satisfies stringent NOx emissions standards
- 10-year warranty
- Water leak detection and scale detection
- Relatively budget-friendly

The condensed steam eliminates energy losses while the ultra-low LOx feature adds peace of mind to the tankless water heaters operations. Finally, with an energy factor of 0.95 and a flow rate of 10-GPM, its Energy Star rating is a warranted power savings attribute.
More costly than some models, the condensing, energy-efficient design partners with a high output rating to make this recommended appliance a superior residential/commercial tankless water heater.
Pros and Cons
- Natural Gas combustion
- No pilot light
- 10-gpm flow rate
- Quiet operation (55-dB)
- High-efficiency condensing operation
- Computer management system
- Rock-bottom LOx emissions
- Energy factor of 0.95 (Energy Star) rating

extras. Take note of the onboard condensate technology, a balanced byproducts compensation mechanism that improves system efficiency. Add to that a maximum BTU rating of 199,000 and a flow rate that peaks at 9.8-GPM, and you have a tankless hot water unit that delivers big on the performance front.
The indoor, natural gas RUC98iN merits its “Ultra” label. The Energy Star tag further underscores its ability to perform as an extremely efficient energy eater, one that’s on a diet thanks to the incorporated condenser tech.
For those who can afford to spend extra but want outstanding performance for their initial investment, the Rinnai RUC98iN Ultra delivers the goods. It’s efficient, compact, and built to instantly heat water in larger redidential and commercial properties.
Pros and Cons
- Sips natural gas
- Ultra-efficient condensing tech
- Compact silver housing
- 0.96 energy factor (Energy Star) rated
- Option for concentric or PVC venting
- Output of 199,000-BTU at 9.8-GPM
- Advanced computer technology and WiFi ready

Built for medium-sized homes, the max 180,000-BTU, 7.5-GPM output power partners with natural gas consumption to better focus your product selecting wit. The optimized output and affordable fuel type also blends with a high-quality build to ensure uncompromising functionality. Other notable features include the ability to adjust the output to either commercial or domestic temperature baselines, a 12-year warranty, and a handy error code indicator. It is, however, a large device, and it needs a venting system.
The Rinnai brand carries some weight. On assessing the RL75iN, that hard-earned reputation has definitely been earned. Powerful enough to provide instant heat to two showering family members at the same time, the 0.82 energy factor rating keeps fuel consumption levels low.
Pros and Cons
- Max. 180,000-BTU
- 7.5-GPM flow rate
- 0.82 energy factor
- Precise MC-91-1US digital controller
- Displays diagnostic error codes
- Fueled by affordable natural gas

If you’re seeking a system that offers a precise temperature control feature, you’ve found that equipment. If energy efficiency and Energy Star compliance are also part of your shopping list, then you’ve definitely arrived at the right product. Only, do realize that a premier build necessitates an equally premier price tag.
The Bosch label is familiar to every savvy consumer. Recommended on every level, the Bosch name assures energy efficient condensing action, super-precise temperature control, and a gift for supplemtal fluid filtration.
Pros and Cons
- Indoor and outdoor installation
- Condensing operation
- Ultra-precise temperature control
- 199,000-BTU, 10.7-GPM max
- Energy factor of 0.96
- Energy Star compliant
- Automated and fully-regulated bypass

Easy to install, the Noritz EZ40-NG fittings exit the top of the compact box. Adding numbers to that ease-of-installation feature, the water heater is equipped with a 120,00-BTU max, a 6.6-GPM flow rate, and a fixed energy factor of 0.89. Translating those figures so that you can judge for yourself whether the device suits your property, the Noritz EZTR40-NG will instantly provide steamy hot water to two showers, although this figure drops slightly if you’re located in a cooler region.
Larger and heavier than most mid-range models in its class, the energy-efficient condensing feature more than makes up for that single drawback. Otherwise, the exceptional craftsmanship applied here combines with a superior build to position the EZTR40-NG solidly among other favorably reviewed tankless models.
Pros and Cons
- A natural gas model
- Energy factor of 0.89
- Installs as a kit to replace tanked heating systems
- Condensing operation
- 120,000-BTU, 6.6-GPM
- Includes a vent Kit and valve kit
- Middling output power
Outdoor natural gas tankless water heater
Rheem RTG-84XLN 8.4 GPM Low NOx Outdoor Tankless Water Heater
Armed with an 180,000-BTU power rating and a remote control pad, the low NOx appliance housing must be mounted outdoors. Due to that feature, the housing is tough and built to defy the lelements.
At this point, the race is on to puncture the budget-priced ceiling. Easy to install, easier to use, the Rheem RTG-84XLN is recommended because it boasts a slew of useful features, including a mid-range capacity, a weather-sealed housing, and that ever-welcome Natural Gas (NG) fuel supply preference.
Pros and Cons
- Fuel source is Natural Gas
- It’s an outdoor appliance
- Vents outdoors
- Low NOx emissions
- Mid-size capacity
- 180,000 BTU at 8.4-GPM
- Energy factor of 0.84
- A 10-year warranty

By the numbers, the device features 199,900-BTU output and a 9.8-GPM flow rate. Tag a 0.88 energy factor rating onto the appliance, then add the realization that this energy-efficient box has enough output power to satisfy a large property. Do, however, realize there are three different venting system options. After that knowledge sinks in and you have the correct fitting on hand, choose whether the NR981-SV-NG is intended for indoor or outdoor mounting.
Loaded with safety features, there’s an embedded freeze protection and overheat protection mechanism built into the device. However, these features, plus the popular brand name, require a little more spending cash.
Pros and Cons
- Sips natural gas
- Rugged housing
- Three venting options
- Indoor and outdoor capable
- Powerful flow rate and energy output
- Coils are made of commercial-grade copper
- Comprehensive safety features

Sporting a 0.82 Energy Factor and a 140,000-BTU, 6.6-GPM capacity, non-condensing technology keeps the outdoor variant of this Takagi-branded unit efficient, although it’s not quite efficient enough to earn an Energy Star award. Being that it’s installed on an outdoor wall, the local climate will impact its abilities. Expect two shower potency in warmer climates, but that two bathroom feature drops to a single shower or bathroom when it’s installed in a cooler region.
Granted, this model is ventless and built to function outside, so it’s designed to coexist with the harshest weather conditions. However, that same weather will impact the appliance’s output power. Still, the affordable Takagi T-KJr2-OS-NG is a recommended light residential usage device, with its low NOx qualities really underlining that endorsement.
Pros and Cons
- Operates on Natural Gas
- Installs outdoors
- Internal freeze protection
- 14,000-BTU 6.6GPM capacity
- Low NOx emissions
- 0.82 Energy Factor
- It’s less than 21-inches tall
- Outdoor cold hampers output
Designed to deliver instant heat to your faucets and shower, to reduces space and to turn your home into an energy efficient haven, the fact remains: not every tankless water heater is created equal. If you want a unit that balances costs against performance, an appliance that fits your properties needs, as well as your own, please do take advantage of this buyer’s guide. Use it to purchase your ideal water heater and to enjoy the comfort offered by the model you intelligently selected.
Is there any OUTDOOR, NG water heater with an EMERGENCY pilot feature so it can function in a power outage?