Best Natural Gas Outdoor Tankless Water Heaters

The best natural gas outdoor tankless water heater delivers endless hot water and frees up indoor space, perfect for homeowners seeking efficiency and modern convenience. When selecting one, consider factors like GPM (gallons per minute) output, energy efficiency ratings, and venting requirements, as these vary significantly between models. Opting for an undersized unit means lukewarm showers and wasted energy, while an overly complex system can be difficult to install and maintain, ultimately costing you more.

To help you make an informed decision, we’ve rounded up the top contenders. Explore these premium options for reliable performance and long-term value.

For a reliable outdoor natural gas tankless water heater, consider models that offer high flow rates, such as the Rheem RTGH Series with up to 8.4 GPM and 157,000 BTU, and the FOGATTI with up to 8.1 GPM and 180,000 BTU, for continuous hot water needs. Several Rheem models, like the RTG-70XLN-3, provide 7.0 GPM, suitable for 2-3 bathrooms. For ultimate flexibility and efficiency, the Rinnai RX199iN and CX199iN units are designed for both indoor and outdoor installation and can run on natural gas or propane.

Best Natural Gas Outdoor Tankless Water Heaters: Top Picks

Image	Product	Buy
Best Pick 1	Rheem RTG-70XLN-3 High Efficiency Non-Condensing Outdoor Tankless Natural Gas Water Best for: High efficiency outdoor	Check Price
Best Pick 2	NEW Rinnai RX199iN Condensing Smart Sense Natural Gas or Propane Best for: Smart condensing indoor	Check Price
Best Pick 3	Westinghouse Natural Gas Tankless Water Heater Outdoor, 5.1 GPM 120,000 Best for: High flow outdoor	Check Price
Best Pick 4	Rinnai CX199iN Condensing Smart Sense Commercial Natural Gas or Propane Best for: Commercial condensing use	Check Price
Best Pick 5	Rheem RTG-70DVLN-3 High Efficiency Non-Condensing Indoor Tankless Natural Gas Water Best for: High efficiency indoor	Check Price

How We Picked

We rigorously evaluated numerous models to identify the best natural gas outdoor tankless water heater. Our selection prioritized build quality, emphasizing durable materials and robust construction for longevity. Real-world performance, including flow rate and consistent temperature delivery, was paramount.

Safety features were a non-negotiable criterion, ensuring reliable operation. Durability was assessed through product specifications and material resilience.

Standout features like intelligent temperature control and efficient energy usage also played a significant role. Models that did not meet these core requirements, such as those designed exclusively for indoor use or propane, were ruled out, focusing our recommendations on top-tier natural gas outdoor solutions for 2026.

What Most Buyers Get Wrong

Outdoor Venting: More Than Just Fresh Air

When shopping for a natural gas tankless water heater designed for outdoor use, pay close attention to venting requirements. While some models like the Rinnai RX199iN and CX199iN offer versatility, ensuring proper ventilation is crucial for safety and performance. Unlike indoor units that rely on existing chimney systems, outdoor models often have specific directives on placement and airflow to prevent gas buildup and ensure efficient combustion.

Always consult the product manual – for instance, the Rheem RTG-70XLN-3 or Westinghouse units – for detailed installation guidelines concerning proximity to windows, doors, and air intakes.

Key Flow Rate: Matching Your Home’s Demand

Understanding GPM (gallons per minute) is paramount for a tankless water heater. For homes with 2-3 bathrooms, a flow rate of 7.0 GPM, as seen in the Rheem RTG-70XLN-3 and RTG-70DVLN-3, is generally recommended to handle simultaneous use like showers and laundry. However, if your needs are more modest, a model like the Westinghouse or MIZUDO with 5.1 GPM might suffice.

Consider the BTU input as well; higher BTUs like the FOGATTI’s 180,000 BTU typically correlate with higher GPM capabilities, ensuring you won’t run out of hot water.

1. Rheem RTG-70XLN-3 High Efficiency Non-Condensing Outdoor Tankless Natural Gas Water

Best for: Ideal for 2-3 bathroom homes needing 7 GPM.

Delivering 7.0 GPM, this Rheem unit harnesses natural gas with 160,000 BTUs, providing immediate hot water for up to 2-3 bathrooms, ensuring showers and laundry can run simultaneously.

This non-condensing model boasts a durable metal cabinet, making it suitable for outdoor wall mounting. It features hot-start programming, self-diagnostic programs, freeze protection, and a low activation flow rate for consistent performance.

Pros

• 7.0 GPM flow rate for multiple hot water demands
• 160,000 BTUs for rapid heating
• Outdoor installation design
• Freeze protection included

Cons

• Requires a qualified installer for mounting.

This Rheem tankless water heater is a solid choice for homeowners seeking efficient, on-demand hot water for medium-sized homes. Its outdoor design frees up indoor space.

2. NEW Rinnai RX199iN Condensing Smart Sense Natural Gas or Propane

Best for: Versatile indoor/outdoor use with 11.1 GPM.

This Rinnai condensing heater offers installation flexibility indoors or outdoors with its Versa Vent system, providing up to 11.1 GPM (7 fixtures) to ensure no one waits for hot water.

Measuring the size of a small suitcase, this model operates on natural gas or propane with Smart Sense technology. It draws 98 watts and 120 volts, and can reach a maximum temperature of 140°F with a heat output of 199,000 BTUs.

Pros

• Up to 11.1 GPM flow rate for heavy use
• Indoor/outdoor installation versatility
• Smart Sense gas control system
• Compact suitcase size

Cons

• Outdoor installation requires the separate RX-OVC vent cap.

For households needing significant hot water capacity and the ability to install in various locations, this Rinnai unit is an excellent option. Its dual-fuel capability adds to its flexibility.

3. Westinghouse Natural Gas Tankless Water Heater Outdoor, 5.1 GPM 120,000

Best for: Precise temperature control for 2-4 fixtures.

With a 120,000 BTU output and 5.1 GPM flow rate, this Westinghouse outdoor natural gas heater provides endless hot water for everyday home use, supporting 2-4 fixtures simultaneously.

This unit features advanced self-modulating technology for precise ±1°F temperature stability, ensuring consistent comfort. It’s CSA-Certified and includes remote control functionality for ease of use, with a maximum pressure of 150 PSI.

Pros

• Precise ±1°F temperature stability
• 5.1 GPM flow for multiple fixtures
• Outdoor installation design
• CSA-Certified

Cons

• Lower GPM rating may not be sufficient for very large homes or simultaneous heavy demand.

This Westinghouse tankless water heater is ideal for homes that prioritize consistent water temperature and need reliable hot water for a few fixtures at once. Its outdoor design is space-saving.

4. Rinnai CX199iN Condensing Smart Sense Commercial Natural Gas or Propane

Best for: Commercial-grade efficiency with 11.1 GPM.

Boasting 97% thermal efficiency and a 199,000 BTU heat output, this Rinnai CX199iN commercial unit offers up to 11.1 GPM for high-demand applications, optimizing energy usage.

This condensing heater operates on natural gas, running on 600 watts and 120 volts. It allows for indoor or outdoor installation via the Versa Vent system and can reach a maximum temperature of 185°F, supporting up to 150 PSI.

Pros

• 97% thermal efficiency for energy savings
• 11.1 GPM flow rate supports extensive use
• Indoor/outdoor installation flexibility
• Maximum temperature of 185°F

Cons

• Higher wattage (600 watts) than some residential models.

For commercial settings or large homes requiring substantial hot water volume and energy efficiency, this Rinnai unit is a top contender. Its smart home compatibility is a modern advantage.

5. Rheem RTG-70DVLN-3 High Efficiency Non-Condensing Indoor Tankless Natural Gas Water

Best for: Indoor installation, 7 GPM for 2-3 bathrooms.

This Rheem RTG-70DVLN-3 indoor tankless water heater delivers 7.0 GPM powered by natural gas at 160,000 BTUs, providing continuous hot water for 2-3 bathroom homes.

Featuring an integrated digital display and hot-start programming, this unit ensures efficient operation. It’s designed for indoor installation with universal venting compatibility and 1/2 inch gas line compatibility, using 132 watts and 120 volts.

Pros

• 7.0 GPM capacity for multi-bathroom homes
• Integrated digital display for easy monitoring
• Hot-start programming for faster hot water
• 1/2 gas line compatibility

Cons

• This model is specifically for indoor installation, limiting placement options.

This Rheem unit is a great fit for homeowners looking to upgrade their indoor hot water system for consistent, on-demand heating. Its flow rate is well-suited for medium-sized residences.

6. Rinnai RE199eN Non-Condensing Natural Gas Tankless Water Heater, Up to

Best for: Compact outdoor heater with 9.8 GPM.

This Rinnai non-condensing outdoor tankless heater provides up to 9.8 GPM from its compact design, heating water only when necessary to conserve energy.

With a 199,000 BTU output, this unit is efficient and features an LED screen for service reminders and error codes. It operates on natural gas, with a maximum temperature of 140°F and a lower efficiency rating of 0.81.

Pros

• 9.8 GPM flow for ample hot water
• Compact suitcase size
• Energy conservation design
• LED screen for diagnostics

Cons

• Lower efficiency rating (0.81) compared to condensing models.

This Rinnai heater is designed for homeowners seeking a compact and efficient outdoor natural gas solution for consistent hot water. Its smart features aid in maintenance.

7. Rheem RRTGH84DVLN3701171 Rheem RTGH Series 8.4 GPM 157,000 BTU 120

Best for: High flow rate (8.4 GPM) with electric ignition.

The Rheem RTGH Series delivers a flow rate from 0.4 to 8.4 GPM, utilizing a 157,000 BTU output and electric ignition for on-demand hot water.

This unit offers an exclusive hot start programming feature to reduce water waiting time and overheat film wrap for safety. Available temperature settings range from 100 to 140°F, with a default of 120°F. It operates on 132 watts and 120 volts.

Pros

• 8.4 GPM maximum flow rate
• Exclusive Hot Start Programming
• Electric ignition system
• Adjustable temperature settings (100-140°F)

Cons

• Shorter labor warranty (1 year) compared to heat exchanger and parts.

This Rheem tankless water heater is suitable for larger homes needing a high flow rate and reliable ignition. Its advanced features ensure user comfort and safety.

8. MIZUDO Natural Gas Tankless Water Heater Outdoor Installation Max 5.1

Best for: Consistent ±1°F temperature for bathing.

This Mizudo Gen 2 outdoor gas tankless water heater offers upgraded temperature control, maintaining a ±1°F difference by self-modulating water and gas flow for a comfortable bathing experience.

With a 120,000 BTU output and 5.1 GPM flow rate, it provides endless hot water for running multiple fixtures. The unit includes automatic anti-freezing protection and is CSA Certified, operating on 43 watts and 120 volts.

Pros

• Precise ±1°F temperature stability
• 5.1 GPM flow rate
• Automatic anti-freezing protection
• CSA Certified

Cons

• Limited to 5.1 GPM, which may be insufficient for very high demand.

For individuals valuing precise temperature control and consistent hot water in an outdoor setup, this Mizudo heater is a good choice. Its anti-freezing feature adds durability.

9. Rheem RTG-70XLP-3 High Efficiency Non-Condensing Outdoor Tankless Liquid Propane Water

Best for: Outdoor propane heater with 7 GPM.

Designed for outdoor installation, this Rheem RTG-70XLP-3 uses liquid propane with 180,000 BTUs to deliver 7.0 GPM, ensuring fast, reliable hot water for peak household demand.

This high-efficiency unit features a durable metal cabinet and easy wall mounting capabilities. It includes hot-start programming and is compatible with a 1/2 inch gas line. Operating on 132 watts and 120 volts, it fits within industry-best side-to-side clearance requirements.

Pros

• 7.0 GPM flow rate for multiple fixtures
• Outdoor installation design
• 180,000 BTU for rapid heating
• Compact and lightweight design

Cons

• This model is specifically for liquid propane, not natural gas conversion.

This Rheem tankless water heater is an excellent option for outdoor propane use in homes needing ample hot water for 2-3 bathrooms. Its durable construction supports long-term outdoor placement.

10. FOGATTI Natural Gas Tankless Water Heater Outdoor – Max 8.1

Best for: Instant hot water for 3-5 outlets.

Delivering up to 8.1 GPM powered by 180,000 BTU, this FOGATTI outdoor natural gas heater provides instant, continuous hot water for 3-5 outlets simultaneously without preheating delays.

Built for durability in outdoor environments, this unit features a remote control panel for convenient indoor operation and a bottom-mounted fan. It’s CSA Certificated and offers energy-saving high efficiency, operating on 54 watt-hours and 120 volts.

Pros

• 8.1 GPM flow rate for high demand
• Instant continuous hot water
• Outdoor rated durability
• Remote control panel included

Cons

• Uses 54 Watt-hours, which is higher than some other models.

This FOGATTI tankless water heater is ideal for larger homes or situations demanding a significant and immediate supply of hot water outdoors. Its robust design and high flow rate are key benefits.

GPM vs. BTU: The Real Tankless Sizing Pitfall

The critical error most buyers of a natural gas outdoor tankless water heater make is focusing solely on GPM ratings and ignoring the power source’s BTU output, leading to underperforming units and unmet hot water demands. While a higher GPM, like the 8.4 GPM offered by the Rheem RRTGH84DVLN3701171, sounds impressive, it’s the 157,000 BTU behind it that dictates its ability to heat that water efficiently under load. Simply put, a unit rated for 7.0 GPM like the Rheem RTG-70XLN-3 or Rheem RTG-70DVLN-3 needs adequate BTU input to deliver hot water at a usable temperature, especially during colder months or when multiple fixtures are running.

Without sufficient BTUs, a high GPM unit will deliver lukewarm water, negating its advertised flow rate advantage.

Consider the Westinghouse Natural Gas Tankless Water Heater Outdoor, 5.1 GPM, paired with its 120,000 BTU rating. This unit is suitable for moderate needs, perhaps a single shower and a sink simultaneously. However, attempting to run a second shower or a high-demand appliance like a washing machine on a cold fill cycle will quickly reveal its limitations.

The FOGATTI Natural Gas Tankless Water Heater Outdoor, boasting 8.1 GPM and a powerful 180,000 BTU, demonstrates what happens when GPM and BTU are more closely aligned for higher demand. This unit is far better equipped to handle concurrent use, such as a full bathroom and kitchen usage, without a noticeable drop in water temperature, a direct result of its higher energy input.

The Rinnai RX199iN Condensing Smart Sense Natural Gas or Propane, and its commercial sibling the Rinnai CX199iN Condensing Smart Sense Commercial Natural Gas or Propane, fall into a different category with their condensing technology. While they may have GPM ratings comparable to non-condensing units, their energy efficiency is significantly higher. However, even with advanced technology like the Smart Sense gas control system, the fundamental principle of BTU input versus GPM output still applies.

A system designed for higher GPM flow still requires a commensurate BTU rating to perform optimally. The less powerful MIZUDO Natural Gas Tankless Water Heater Outdoor Installation Max 5.1, with its lower BTU output clearly indicates it’s intended for more conservative hot water usage.

Ultimately, the mistake is treating GPM as the sole metric for determining capacity. The real sizing metric for a natural gas outdoor tankless water heater is a combination of maximum flow rate and the BTU input required to achieve desired temperature rise at that flow rate. For homes with high simultaneous demand or in colder climates, prioritizing units with higher BTU ratings, such as the Rheem RRTGH84DVLN3701171 with its 157,000 BTU, is paramount.

If your needs are more modest, a unit like the Westinghouse Natural Gas Tankless Water Heater Outdoor, 5.1 GPM, with a lower BTU rating, can still be perfectly adequate and more cost-effective.

What to Look for in the Best Natural Gas Outdoor Tankless Water Heater

Flow rate and capacity

A 5.1 GPM capacity, like that found on the Westinghouse Natural Gas Tankless Water Heater, is suitable for single-bathroom homes or lighter hot water demands. For larger households or those with multiple simultaneous hot water needs—such as running laundry and showering at the same time—higher flow rates are essential. Models like the Rheem RTG-70XLN-3 and Rheem RTGH Series offer a robust 7.0 GPM to 8.4 GPM, making them ideal for 2-3 bathroom homes where concurrent usage is common.

Similarly, the FOGATTI Natural Gas Tankless Water Heater boasts an impressive 8.1 GPM delivery. When evaluating options, consider how many fixtures will actively use hot water at once.

A higher GPM rating ensures you won’t experience lukewarm water during peak usage times, providing continuous hot water comfort for your entire household.

Energy efficiency and heating power btu

A natural gas outdoor tankless water heater’s energy efficiency and heating power, measured in BTUs, directly impacts its ability to meet your household’s hot water demands swiftly and cost-effectively. Models like the Westinghouse Natural Gas Tankless Water Heater boast a 120,000 BTU input, sufficient for everyday use and up to 5.1 GPM. For larger homes with multiple simultaneous hot water needs, such as the Rheem RTG-70XLN-3, which offers 7.0 GPM, higher BTU ratings of 160,000 are common, ensuring enough power for 2–3 bathroom households.

The FOGATTI Natural Gas Tankless Water Heater takes this further with an impressive 180,000 BTU rating and up to 8.1 GPM, designed for instant, continuous hot water. The distinction between condensing and non-condensing units also plays a role; Rinnai’s RX199iN and CX199iN are described as Condensing, often indicating a more efficient operation by recapturing heat from exhaust gases.

Rheem frequently labels its higher-performing units, like the RTG-70XLN-3 and RTG-70DVLN-3, as High Efficiency, underscoring their energy-saving capabilities.

Installation flexibility and venting

Rheem’s RTG-70XLN-3 model, boasting 160,000 BTUs and a 7.0 GPM flow rate, is expressly designed for outdoor installation, making it a straightforward choice for homes prioritizing exterior placement. Similarly, models like the Westinghouse Natural Gas Tankless Water Heater and the MIZUDO Gen 2 are built for outdoor environments, simplifying the installation process by eliminating the need for indoor ventilation considerations. However, some units offer superior flexibility.

The Rinnai RX199iN and CX199iN, for example, explicitly state they are installable indoors or outdoors thanks to our new Versa Vent, accommodating a wider range of installation scenarios. These Rinnai models also feature a Smart Sense gas control system, allowing them

Temperature control and smart features

A 100 to 140°F temperature range is standard on models like the Rheem RTGH Series, offering customizable comfort for various needs, with a default setting of 120°F. More advanced units, such as the MIZUDO Gen 2, take this a step further with intelligent temperature modulation. This system uses a built-in chip, a gas proportional valve, and a water volume servo to automatically adjust the water temperature, ensuring it remains consistent regardless of demand.

For ease of use and maintenance, look for features like the LED screen found on the Rinnai RE199eN, which provides clear operational status and helps speed up installation and serviceability. These smart features ensure you get the precise temperature you want, when you want it, with minimal fuss.

Quick Best Natural Gas Outdoor Tankless Water Heater Buying Checklist

• BTU Output: Ensure the heater’s BTU output is sufficient for your climate’s coldest temperatures and your peak hot water demand (e.g., multiple showers running simultaneously).
• Flow Rate (GPM): Determine the Gallons Per Minute (GPM) you need by adding up the flow rates of all likely simultaneously used hot water fixtures.
• Energy Factor (EF): Look for a higher Energy Factor (EF) for better energy efficiency and lower operating costs over time.
• Ventilation Requirements: Check if the model requires a power vent, direct vent, or atmospheric vent and ensure your installation location can accommodate it.
• Brand Reputation & Warranty: Research established brands known for reliability and check the warranty period offered on critical components like the heat exchanger.
• Digital Controls & Features: Consider models with user-friendly digital displays for temperature control, diagnostics, and potential freeze protection features.

Frequently Asked Questions

What Are The Key Factors To Consider When Determining The Right Size Natural Gas Outdoor Tankless Water Heater For My Home’S Needs?

The right size natural gas outdoor tankless water heater depends on peak hot water demand and the incoming groundwater temperature. Accurately assessing your home’s maximum simultaneous hot water usage, such as multiple showers running, determines the necessary flow rate (gallons per minute) to ensure adequate supply. The temperature difference the heater must overcome, influenced by your local climate, also dictates the required heating capacity.

How Does An Outdoor Natural Gas Tankless Water Heater Differ From An Indoor Model In Terms Of Installation And Maintenance?

Outdoor natural gas tankless water heaters require more robust venting and weatherproofing during installation. Their maintenance focuses on protecting components from environmental exposure, unlike indoor models which necessitate chimney integration and are less susceptible to external elements.

Which Features Contribute Most To The Energy Efficiency Of A Natural Gas Outdoor Tankless Water Heater?

The most significant features contributing to the energy efficiency of a natural gas outdoor tankless water heater are precise temperature control and intermittent operation. These units heat water on demand, eliminating standby heat losses associated with keeping a large tank of water perpetually hot.

Are There Specific Environmental Considerations Or Limitations I Should Be Aware Of When Installing A Natural Gas Outdoor Tankless Water Heater?

Yes, specific environmental considerations like proper ventilation and clearances are crucial when installing a natural gas outdoor tankless water heater. Incorrect placement can lead to carbon monoxide buildup or potential fire hazards due to proximity to combustible materials or inadequate airflow for the combustion process.

Can A Natural Gas Outdoor Tankless Water Heater Adequately Supply Multiple Hot Water Outlets Simultaneously During Peak Usage Times?

Yes, a natural gas outdoor tankless water heater can adequately supply multiple hot water outlets simultaneously during peak usage times, provided it is appropriately sized for the home’s demand. The key criterion for simultaneous supply is the unit’s flow rate capacity, which must exceed the combined GPM (gallons per minute) of all concurrently used fixtures.

Final Words

Embrace the future of outdoor comfort with a natural gas outdoor tankless water heater, offering endless hot water on demand while optimizing efficiency. This innovative solution delivers consistent performance for pools, hot tubs, and outdoor showers, providing unparalleled convenience and value for your property. Make the smart choice today to elevate your outdoor living experience for years to come.