This post may contain affiliate links, which means we may receive a commission at no cost to you if you make a purchase through a link.
Choosing the best tankless water heater gas can make a big difference in daily comfort, especially if you want steady hot water without the bulk of a storage tank. The models in this list range from compact, budget-friendly units to high-capacity whole-home heaters, so there’s something here for different household sizes and installation needs.
When comparing options, pay close attention to flow rate, BTU output, indoor or outdoor installation type, fuel type, and whether the unit is condensing or non-condensing. It also helps to think about how many fixtures you use at once, because a heater that works well for one home may feel underpowered in another.
Let’s get started!
Our Top Picks at a Glance
| Product | Best For | Buy Now |
|---|---|---|
| Rinnai RX199iN | High-capacity whole-house use | Buy |
| Rheem RTG-84XLN-3 | Outdoor natural gas installation | Buy |
| Rinnai RE199iN | High flow indoor whole-house heating | Buy |
Best Tankless Water Heater Gas
1. Best Overall: Rinnai RX199iN
- One Model, Anywhere: This Rinnai tankless water heater is installable indoors or outdoors thanks to our new Versa Vent and powered by either propane or natural gas thanks to a Smart Sense gas control system; RX-OVC vent cap required for outdoor install
- Never Run Out of Hot Water with this Compact Tankless Gas Water Heater: This condensing propane and natural gas tankless water heater from Rinnai is only the size of a small suitcase, but provides up to 11.1 GPM (7 fixtures at once)
- Smart, Efficient Design: This water heater's modern design includes an easy-to-use interface, Quick Flush feature for simplified flushing, as well as a super-high energy efficiency factor of UEF .98; See Controlr module for WiFi control (not included)
The Rinnai RX199iN is a high-output tankless water heater designed for households that need a strong hot water supply. With up to 11.1 GPM and 199,000 BTU, it is positioned as one of the most powerful options in this list. It is also built for either indoor or outdoor installation, which adds flexibility depending on your setup.
This model stands out for larger homes or families that use several fixtures at once. Its condensing design and smart sense positioning make it a premium choice in the lineup, especially if you want a whole-home solution. The fuel flexibility of natural gas or propane is another practical advantage.
If your priority is performance and installation versatility, this is one of the strongest picks in the roundup. It sits at the higher end of the price range, but the specifications reflect that premium position.
Pros
- Up to 11.1 GPM
- 199,000 BTU output
- Indoor or outdoor installation
- Natural gas or propane compatibility
Cons
- Higher price point
- May be more than smaller households need
2. Best Value: ThermoMate CZ422NG
- [Max 5 GPM & 113,000 BTU] – The ThermoMate instant hot water heater delivers hot water on-demand for two showers at the same time, maintaining a stable 105°F (based on 65°F inlet temperature). No waiting, no cold-water interruptions—perfect for busy homes. Its smart flow sensor and control chip adjust heating 20,000 times per second, ensuring ±1°F temperature consistency.
- [Safety & Reliable] - This gas tankless water heater integrates 8 protections: boil-dry, freeze, flame-out, overheating, over-temperature, pipe blockage, high-temperature lock, and excessive air pressure. Equipped with 4 ceramic heating cores, it auto-activates frost protection when temperatures hit 41°F (5℃). The energy-smart system uses minimal electricity to generate gentle warmth, preventing pipe ice buildup without high energy costs.
- [Energy Efficient & Save Money] - The heat exchanger is constructed from high-quality oxygen-free copper, providing superior thermal conductivity and corrosion resistance compared to stainless steel. It achieves a thermal efficiency of 98% (vs. 80% for stainless steel models) and boasts a uniform energy factor (UEF) of 0.81. This design reduces energy waste, lowering annual operating costs by approximately 30% versus traditional systems.
The ThermoMate CZ422NG is a budget-friendly natural gas tankless water heater with up to 5 GPM and 113,000 BTU. It is aimed at indoor residential use and comes with multi-point heating support for household hot water demands. For buyers trying to keep costs lower, it offers a straightforward entry point into tankless systems.
Its compact capacity makes it more suitable for smaller homes or lighter hot water use rather than large families with simultaneous high demand. Still, it can be a sensible choice when you want instant on-demand hot water without paying for a larger premium unit.
If you are looking for one of the more affordable natural gas options in this group, this model deserves attention. It balances basic whole-house usability with a lower purchase price.
Pros
- Lower price than many competitors
- Up to 5 GPM
- 113,000 BTU output
- Indoor residential use
Cons
- Lower flow rate than larger models
- Not ideal for bigger households
3. Best for Large Families: MIZUDO Natural Gas Tankless Water Heater
- [Professional 199k BTU Tankless Water Heater]: Experience uninterrupted hot water delivery with 10.3 GPM flow capacity, designed to support large households with 5-7 fixtures simultaneously, providing hot water only when needed, making it an economically smart choice
- [Smart WiFi Connectivity for Remote Management]: Control and monitor your gas tankless water heater from anywhere using the dedicated mobile application. Adjust temperature settings, create custom schedules, receive maintenance alerts, and track energy usage through your smartphone
- [Comprehensive Safety Protection]: Features 16+ integrated safety mechanisms including freeze protection (-13°F operational), anti-dry firing, flame failure detection, exhaust blockage monitoring, and automatic shutdown systems
The MIZUDO Natural Gas Tankless Water Heater is built for higher-demand homes, offering up to 10.3 GPM and 199,000 BTU. It is designed for indoor installation and is marketed as suitable for large families and residential whole-house use. The WiFi and app control features add convenience for users who want connected functionality.
This unit’s high output makes it a strong fit for homes that may have several hot water fixtures in use at one time. Its non-condensing design keeps it within the standard gas tankless category while still targeting efficient residential performance.
For households that want strong flow and smart control in a single package, this is a compelling choice. It offers near top-tier capacity without moving into commercial-level pricing.
Pros
- Up to 10.3 GPM
- 199,000 BTU output
- WiFi and app control
- Good for large families
Cons
- Indoor installation only
- Non-condensing design
4. Best for Smart Control: Westinghouse Smart Tankless Water Heater Gas
- 【Endless Hot Water for the Whole Home】Enjoy continuous instant hot water for showers, laundry, dishwashing, and daily household use. Delivering up to 7.9 GPM and 180,000 BTU, this whole house tankless water heater comfortably supports 3–5 fixtures simultaneously without sacrificing comfort or water pressure.
- 【Smart WiFi App Control】Control your indoor tankless water heater anytime through the smartphone app or LED display panel. Easily adjust water temperature, monitor operating status, and enjoy a smarter, more convenient hot water experience for your home.
- 【Precise ±1°F Temperature Stability】Advanced self-modulating technology automatically adjusts gas and water flow to maintain consistent water temperature within ±1°F. Enjoy stable, spa-like comfort with fewer cold bursts and reduced temperature fluctuations during every shower.
The Westinghouse Smart Tankless Water Heater Gas provides up to 7.9 GPM and 180,000 BTU, making it a strong residential choice for multiple fixtures. It is designed for indoor use and includes WiFi app control, along with ±1°F temperature stability. Those features make it attractive for users who want more precise operation.
Its 7.9 GPM rating places it in the middle-to-upper range, which should suit many family homes. The non-condensing setup keeps the product focused on straightforward gas tankless performance, while the smart features add modern convenience.
This is a solid option if you want a dependable whole-home heater with app-based control. It blends a good balance of power and convenience.
Pros
- 7.9 GPM output
- 180,000 BTU rating
- WiFi app control
- ±1°F temperature stability
Cons
- Indoor installation only
- Non-condensing design
5. Best Indoor Natural Gas: Rheem RTG-70DVLN-3
- High-efficiency tankless gas water heater delivers up to 7.0 GPM, perfect for 2–3 bathroom homes with multiple hot water needs like showers and laundry.
- Powered by natural gas with 160,000 BTUs, this durable tankless unit ensures fast, reliable hot water—even during peak household demand.
- Designed for indoor installation, this high-efficiency tankless natural gas water heater features a durable, compact metal cabinet and supports easy wall mounting by a qualified installer.
The Rheem RTG-70DVLN-3 is a high-efficiency non-condensing indoor tankless water heater with 7.0 GPM and 160,000 BTUs. It is a natural gas unit built for indoor installation, making it a practical fit for standard residential use. Rheem’s lineup is known for dependable options, and this model reflects that focused approach.
With 7.0 GPM, this heater is suitable for many households that need a steady supply for daily hot water tasks. It is not the biggest model in the list, but its balance of output and efficiency may be enough for moderate demand.
If you want a recognizable brand and a simple indoor natural gas setup, this is a dependable candidate. It sits in a comfortable middle ground between compact and high-capacity choices.
Pros
- 7.0 GPM flow rate
- 160,000 BTUs
- Indoor natural gas design
- High-efficiency non-condensing build
Cons
- Not the highest flow rate in the list
- Indoor installation only
6. Best for Outdoor Use: Rheem RTG-84XLN-3
- High-efficiency tankless gas water heater delivers up to 8.4 GPM, perfect for 2–3 bathroom homes with multiple hot water needs like showers and laundry.
- Powered by natural gas with 180,000 BTUs, this durable tankless unit ensures fast, reliable hot water—even during peak household demand.
- Designed for outdoor installation, this high-efficiency tankless natural gas water heater features a durable metal cabinet and supports easy wall mounting by a qualified installer.
The Rheem RTG-84XLN-3 is an outdoor natural gas tankless water heater rated at 8.4 GPM and 180,000 BTUs. Its outdoor format makes it a practical solution for homes that prefer to keep the heater outside and avoid an indoor installation footprint. That can be especially useful where indoor utility space is limited.
With stronger flow than several midrange models, this heater is positioned well for homes that need broader hot water support. The outdoor design also helps make installation planning simpler for some setups, depending on local conditions and requirements.
This is a strong choice if outdoor mounting is a priority and you still want solid residential output. Among the outdoor options, it is one of the most appealing picks.
Pros
- Outdoor installation
- 8.4 GPM flow rate
- 180,000 BTUs
- High-efficiency non-condensing design
Cons
- Outdoor-only setup
- Higher price than some alternatives
7. Best Mid-High Capacity: Rheem RRTGH84DVLN3701171
- Flow rate of 0.4 - 8.4 GPM
- Available temperature settings range from 100 to 140F (default setting of 120F)
- Includes electric ignition
The Rheem RRTGH84DVLN3701171 offers 8.4 GPM and 157,000 BTU in a residential indoor natural gas format. It includes a stainless steel build and runs on 120 volts, which may appeal to buyers looking for a premium-feeling indoor heater. Its flow rate makes it well suited to homes with moderate to heavier hot water needs.
This model sits in a useful middle-high capacity range, giving it flexibility for families that want more than a basic unit. While it does not match the largest output models in the list, it still offers strong everyday performance.
If you like the Rheem brand and want a stainless steel indoor unit with strong residential output, this model is worth comparing closely. It brings a balance of capacity and build quality.
Pros
- 8.4 GPM flow rate
- Stainless steel construction
- Indoor natural gas design
- 120 volt operation
Cons
- Lower BTU rating than top-capacity units
- Indoor installation only
8. Best Propane Indoor: Rheem RTG-70DVLP-3
- High-efficiency tankless gas water heater delivers up to 7.0 GPM, perfect for 2–3 bathroom homes with multiple hot water needs like showers and laundry.
- Powered by liquid propane with 160,000 BTUs, this durable tankless unit ensures fast, reliable hot water—even during peak household demand.
- Designed for indoor installation, this high-efficiency liquid propane tankless gas water heater features a durable, compact metal cabinet and supports easy wall mounting by a qualified installer.
The Rheem RTG-70DVLP-3 is the propane version of a high-efficiency non-condensing indoor tankless water heater. It offers 7.0 GPM and 160,000 BTUs, making it a practical choice for propane users who want steady on-demand hot water indoors. The specifications are close to the natural gas model in the same range.
This heater is a smart match for homes that use liquid propane rather than natural gas and still need a reliable residential system. Its output is suitable for many standard household uses, though larger families may want to step up to a higher-capacity unit.
If propane is your fuel source, this model deserves a place on the shortlist. It delivers familiar Rheem performance in a propane-specific format.
Pros
- Propane fuel type
- 7.0 GPM output
- 160,000 BTUs
- Indoor high-efficiency design
Cons
- Indoor installation only
- Not as powerful as top whole-house options
9. Best Rinnai Alternative: Rinnai RE199iN
- Energy Efficient On-Demand Performance. Non-condensing natural gas tankless water heater heats water only when needed, reducing standby energy loss compared to traditional tank water heaters. Compact, space-saving wall-mounted design features an LED display with diagnostic codes and service reminders for easier maintenance and long-term reliability.
- Endless Hot Water – Up to 9.8 GPM, 199,000 BTU. High-performance 199,000 BTU gas tankless water heater delivers up to 9.8 gallons per minute, supporting multiple fixtures at once—ideal for whole house use including showers, laundry, dishwasher, and large households. Reliable indoor on-demand hot water without a bulky storage tank.
- Durable Construction with Industry-Leading Warranty. Built for residential performance, this indoor natural gas tankless hot water heater includes a 15-year limited warranty on the heat exchanger, 5-year on parts, and 1-year on labor. Compatible with Rinnai Controlr module (sold separately) for WiFi monitoring and smart home integration. For built-in recirculation, see REP199iN model.
The Rinnai RE199iN is a non-condensing natural gas tankless water heater with 199,000 BTU and up to 9.8 GPM. It is built for indoor whole-house installation and is aimed at users who want strong on-demand hot water from a well-known brand. Its output places it among the higher-capacity residential options.
With nearly 10 GPM available, this model can handle demanding household use more confidently than smaller units. It is a natural fit for families that want a whole-home heater with a strong performance profile and indoor installation.
This is a good option if you want Rinnai quality and high flow without moving into the RX series above it. It remains one of the more capable choices in the lineup.
Pros
- Up to 9.8 GPM
- 199,000 BTU output
- Indoor whole-house installation
- Strong brand recognition
Cons
- Higher price than basic units
- Non-condensing design
10. Best Outdoor Propane: Rheem RTG-70XLP-3
- High-efficiency tankless gas water heater delivers up to 7.0 GPM, perfect for 2–3 bathroom homes with multiple hot water needs like showers and laundry.
- Powered by liquid propane with 160,000 BTUs, this durable tankless unit ensures fast, reliable hot water—even during peak household demand.
- Designed for outdoor installation, this high-efficiency liquid propane tankless gas water heater features a durable metal cabinet and supports easy wall mounting by a qualified installer.
The Rheem RTG-70XLP-3 is an outdoor liquid propane tankless water heater with 7.0 GPM and 160,000 BTUs. It is a practical option for propane-powered homes that prefer an outdoor installation. Its design mirrors the outdoor natural gas category but for LP users.
This model is a sensible fit for households that need a solid outdoor heater without requiring the highest-capacity output. It can serve as a straightforward solution for daily hot water use with a space-saving outdoor placement.
If your home runs on propane and you want the heater outside, this unit is a worthy contender. It keeps the setup simple and focused.
Pros
- Outdoor installation
- Propane fuel type
- 7.0 GPM flow rate
- 160,000 BTUs
Cons
- Outdoor-only unit
- Midrange capacity
11. Best Compact Outdoor: Rinnai V53DeN
- Unlimited Hot Water For Your Family: Enjoy endless hot water with our Rinnai tankless hot water heater, providing a flow rate of 5.3 GPM to serve up to 4 appliances; Say goodbye to cold showers and hello to convenience with this efficient unit
- Energy Efficiency At Its Best: This compact gas tankless water heater conserves energy by heating water only when needed, making it an earth-friendly choice for energy-conscious homeowners; Reduce utility bills and enjoy hot water as needed
- Peace Of Mind With Long-Lasting Performance: The Rinnai tankless hot water heater offers a 10-year warranty on the heat exchanger, ensuring durability; Enjoy uninterrupted hot water flow without worrying about frequent repairs
The Rinnai V53DeN is a natural gas tankless water heater with 5.3 GPM and outdoor installation. It is one of the more compact capacity options in this list, which makes it suitable for smaller households or lighter hot water demand. The outdoor format also helps reduce indoor space requirements.
This model is a practical pick if you do not need the high output of larger whole-house units. Its size and outdoor setup make it more approachable for homes with simpler hot water needs.
If you want a basic outdoor Rinnai option that keeps things manageable, this model fits that role well. It is especially appealing for buyers who value simplicity.
Pros
- Outdoor installation
- Natural gas fuel type
- 5.3 GPM flow rate
- Compact compared with larger whole-house units
Cons
- Lower flow rate than bigger models
- Outdoor-only setup
12. Best Commercial-Grade: Rinnai CX199iN
- One Model, Anywhere: This Rinnai tankless water heater is installable indoors or outdoors thanks to our new Versa Vent and powered by either propane or natural gas thanks to a Smart Sense gas control system; RX-OVC vent cap required for outdoor install
- Super High Efficiency for Lower Energy Costs: Boasting an impressive thermal efficiency rating of 97%, this tankless water heater optimizes energy usage, helping to significantly reduce operational costs
- Installation Flexibility with Conversion Kit: This model provides installation flexibility with an optional conversion kit for recirculation; With the kit, users can improve hot water management, optimizing efficiency and saving energy
The Rinnai CX199iN is a condensing smart sense commercial natural gas or propane tankless water heater with 199,000 BTU. It is positioned for commercial use and offers fuel flexibility, which makes it a higher-capacity option in this list. The premium pricing reflects that positioning.
Because it is a commercial model, it is best considered by buyers with heavier duty requirements than a standard home might need. It stands out for its strong BTU rating and broader fuel compatibility.
If you are comparing higher-end tankless gas systems and need commercial-grade positioning, this is a notable pick. It is built for bigger expectations than a typical residential unit.
Pros
- Commercial-grade positioning
- 199,000 BTUs
- Natural gas or propane compatibility
- Condensing design
Cons
- High price
- May be more than most homes need
13. Best Electric Alternative 18kW: Rheem 18kW 240V
- External digital thermostatic control with LED display (+/1 degree accuracy)
- Most advanced self-modulation, adjust power to meet hot water demand
- Durable Copper immersion two heating elements, field Serviceable. Flow Rate- up to 4.4 GPM
The Rheem 18kW 240V Tankless Electric Water Heater is included as an alternative option for buyers comparing tankless systems more broadly. It is not a gas unit, but it can still be useful for readers who are weighing installation and utility differences. The gray finish and electric design make it a separate category from the gas models above.
Because it is electric, it will appeal to a different type of setup than the natural gas and propane heaters in this article. Its capacity and behavior will depend heavily on electrical requirements and household demand.
If you are strictly shopping for gas, this model is not the primary match. However, it remains a comparison point for those exploring tankless water heater options overall.
Pros
- Tankless electric design
- 240V operation
- Compact alternative option
Cons
- Not a gas model
- Outside the main keyword focus
14. Best High Flow Propane: Rheem RRTGH95DVLP3701178
- Flow rate of 0.4 - 9.5 GPM
- Available temperature settings range from 100 to 140F (default setting of 120F)
- Includes electric ignition
The Rheem RRTGH95DVLP3701178 is a residential indoor liquid propane tankless water heater with 9.5 GPM and 199,900 BTUs. It is a strong high-flow option for propane households that need serious whole-home hot water support. The stainless steel construction adds to its premium positioning.
Its flow rating makes it one of the more capable propane models in the lineup. For busy homes with multiple demand points, that extra capacity can make a meaningful difference in day-to-day use.
If you need a high-capacity propane heater from a trusted brand, this model should be on your list. It is one of the strongest LP options here.
Pros
- 9.5 GPM output
- 199,900 BTUs
- Stainless steel construction
- Indoor propane design
Cons
- Premium price
- Indoor installation only
15. Best Budget Natural Gas: Ranein Natural Gas Tankless Water Heater
- Powerful On-Demand Heating: 100,000 BTU & 4.3 GPM for this tankless water heater gas, supports 3-4 water points simultaneously, delivers endless hot water on demand with no waiting.
- 4 Intelligent Preset Modes: One-click switch for 4-season/Kitchen/Bathtub/Shower modes; 4-season auto-matches temp, kitchen defaults to 100°F, bathtub supports 50-800L volume adjustment.
- Precision Temp Control: Gas-water-temperature intelligent linkage, 95°F-155°F adjustable range, high-temp lock prevents scalding, safe for kids and elders.
The Ranein Natural Gas Tankless Water Heater is an indoor model with a maximum of 4.3 GPM and 100,000 BTU. It is one of the most affordable products in this roundup, making it attractive for budget-conscious shoppers who want a basic gas tankless solution. Its compact output suits lighter household demand.
This unit is best viewed as a smaller-capacity option for simpler hot water needs rather than a large family system. It offers instant hot water capability in a straightforward indoor format.
If cost is the main deciding factor, this heater is worth considering. It gives you a low entry price into natural gas tankless water heating.
Pros
- Very affordable price
- Indoor natural gas model
- Basic on-demand hot water
- Compact capacity for smaller homes
Cons
- Only up to 4.3 GPM
- Lower BTU output than larger units
Buying Guide
Flow Rate
Flow rate, measured in gallons per minute, helps you understand how much hot water a unit can supply at once. If your home frequently uses multiple fixtures together, a higher GPM rating is usually more practical.
BTU Output
BTU output gives you an idea of heating power. In general, a higher BTU rating supports stronger performance, especially when several taps or appliances are drawing hot water at the same time.
Indoor vs. Outdoor Installation
Some models are made for indoor installation, while others are designed for outdoor placement. Choosing the right setup depends on your available space, local climate, and how you want the unit installed.
Natural Gas vs. Propane
Fuel type matters. Make sure the unit matches your home’s gas supply, since a natural gas model and a propane model are not interchangeable without the right specifications.
Condensing vs. Non-Condensing
Condensing and non-condensing units differ in design and efficiency approach. If you are narrowing down the Best Tankless Water Heater Gas options, this is one of the core details to check before buying.
Smart Features
Some units include WiFi or app control, which can add convenience. If remote monitoring or more precise temperature management is important to you, those features may be worth paying attention to.
Frequently Asked Questions
What size tankless gas water heater do I need?
The right size depends on how many hot water fixtures you use at the same time. Larger households or homes with multiple bathrooms often need higher GPM and BTU ratings than smaller homes.
Is a higher BTU always better?
Not always. A higher BTU rating can support more hot water output, but you should still match the unit to your home’s actual hot water needs and installation type.
Should I choose indoor or outdoor installation?
That depends on your space and setup. Indoor models keep the unit inside the home, while outdoor models can save indoor space and may simplify some installations.
Can I use propane instead of natural gas?
Only if the unit is built for propane. Always confirm the fuel type before buying because natural gas and propane models are not the same.
Are smart features necessary?
No, but they can be helpful. WiFi or app control may make it easier to monitor or adjust the heater, though many buyers are perfectly happy with a standard non-smart model.
Conclusion
The Best Tankless Water Heater Gas for you will depend on your household size, fuel type, installation preference, and budget. If you want maximum output and flexibility, the Rinnai RX199iN is a standout. If you need a lower-cost entry point, the ThermoMate CZ422NG and Ranein models are more accessible choices.
For outdoor installation, the Rheem RTG-84XLN-3 is especially appealing, while the MIZUDO and Westinghouse models add smart features for buyers who want modern convenience. No matter which one you choose, focusing on flow rate, BTU output, and fuel compatibility will help you pick the right unit for your home.