Gas tankless water heaters have revolutionized how homeowners access hot water, providing on-demand heating without the limitations of traditional tank systems. These efficient units heat water only when needed, eliminating standby energy losses and providing endless hot water. Whether you’re looking to upgrade your existing system or installing a new water heater, choosing the right gas tankless model can significantly impact your home’s efficiency and comfort level.
In this comprehensive guide, we’ll examine the top gas tankless water heaters on the market, comparing their flow rates, BTU ratings, installation requirements, and special features. From whole-house systems capable of handling multiple fixtures simultaneously to compact units perfect for smaller households, we’ve selected models that represent the best in performance, reliability, and value.
| Model | Flow Rate | BTU Rating | Installation | Best For |
|---|---|---|---|---|
| Rinnai RX199iN | 11.1 GPM | 199,000 BTU | Indoor/Outdoor | Large homes with multiple fixtures |
| Rheem RTG-95DVLN-3 | 9.5 GPM | High Efficiency | Indoor | Medium to large households |
| FOGATTI Comfort 180S | 8.1 GPM | 180,000 BTU | Outdoor | Multi-fixture homes needing outdoor installation |
| ThermoMate | 4.7 GPM | 102,000 BTU | Indoor | Medium-sized households |
| Ranein | 3.6 GPM | 80,000 BTU | Indoor | Small households or point-of-use applications |
#1 Rinnai RX199iN Condensing Smart Sense Gas Tankless Water Heater
The Rinnai RX199iN represents the pinnacle of gas tankless water heater technology, offering exceptional performance for large households with high hot water demands. This powerhouse unit delivers an impressive 11.1 gallons per minute (GPM), enough capacity to supply up to seven fixtures simultaneously without any drop in temperature or pressure. When multiple showers, dishwashers, or washing machines are running concurrently, this model maintains consistent hot water delivery throughout your home.
One of the most versatile options on the market, the RX199iN features Rinnai’s innovative Smart Sense gas control system that works with either natural gas or propane, eliminating the need to purchase a specific model for your fuel type. The unit’s Versa Vent technology provides installation flexibility, allowing for both indoor and outdoor placement depending on your home’s configuration and space constraints.
Despite its powerful 199,000 BTU output, this unit achieves a remarkable 0.98 UEF (Uniform Energy Factor), making it one of the most efficient gas tankless water heaters available. This super-high efficiency rating translates to lower utility bills and reduced environmental impact. The condensing technology captures additional heat from exhaust gases that would otherwise be wasted, maximizing energy utilization.
The user-friendly interface simplifies temperature adjustments and maintenance monitoring, while the Quick Flush feature streamlines routine maintenance to extend the unit’s operational life. Though not included with the base unit, the optional Controlr module enables Wi-Fi connectivity for remote temperature adjustments and system monitoring from your smartphone.
With its compact design—about the size of a small suitcase—the RX199iN saves valuable space compared to traditional tank systems while delivering superior performance and endless hot water. This premium unit is ideal for larger homes with high simultaneous hot water demands or for homeowners who never want to worry about running out of hot water again.
#2 Rheem RTG-95DVLN-3 High Efficiency Indoor Tankless Water Heater
The Rheem RTG-95DVLN-3 stands out as a top-tier indoor tankless water heater that balances impressive performance with energy efficiency. With a 9.5 GPM flow rate, this non-condensing unit can comfortably handle multiple hot water demands simultaneously, making it perfect for medium to large households that frequently use hot water in different areas of the home at once.
Designed specifically for indoor installation, this Rheem model delivers continuous hot water throughout your home even during peak usage times. Whether you’re running a shower while the dishwasher is operating, or multiple family members need hot water at once, the RTG-95DVLN-3 eliminates the frustration of running out of hot water mid-shower or having to schedule hot water usage among family members.
What sets this model apart is its water-saving capabilities. The innovative water-saving setting can conserve up to 1,100 gallons of water annually—a significant environmental benefit that also translates to lower water bills. This feature is especially valuable in regions facing water restrictions or for environmentally conscious homeowners looking to reduce their resource consumption.
The unit’s high-efficiency design ensures it only operates when hot water is demanded, eliminating the standby heat loss common with traditional tank systems. This on-demand heating approach means you’ll see noticeable energy savings reflected in your utility bills over time, particularly if you’re upgrading from an older tank-style water heater.
Installation requirements include proper venting and gas line sizing, but once properly installed, the RTG-95DVLN-3 offers reliable, consistent performance with minimal maintenance needs. For households that value efficiency, consistent hot water supply, and the space-saving benefits of tankless technology, this Rheem model delivers exceptional value and performance.
#3 FOGATTI Natural Gas Tankless Water Heater For Outdoor Installation
The FOGATTI Comfort 180S Series is an exceptional outdoor tankless water heater designed for homeowners who need a powerful, weather-resistant solution for their hot water needs. With an impressive 8.1 GPM flow rate powered by 180,000 BTU of heating capacity, this unit can effortlessly handle 3-5 water outlets simultaneously, making it ideal for families that require hot water at multiple locations throughout the home.
As a dedicated outdoor unit, the FOGATTI eliminates indoor venting requirements while freeing up valuable interior space. The thoughtfully engineered design includes a bottom-mounted fan that prevents smoke backflow and ensures stable combustion regardless of weather conditions. This feature enhances both safety and durability, contributing to a longer operational lifespan even when exposed to the elements.
One of the standout features is the included remote control panel, which allows for convenient indoor temperature adjustments without having to go outside to the unit. This user-friendly approach means you can easily modify settings from the comfort of your home, regardless of weather conditions outside.
Temperature consistency is a hallmark of this model, thanks to its advanced water servo technology and precision temperature sensors. The system continuously adjusts water flow and gas intake to maintain temperature within an impressive ±1°F of your setting. This four-stage combustion system ensures you’ll experience the same comfortable shower temperature during frigid winter mornings and hot summer evenings alike.
The FOGATTI’s outdoor design makes it particularly well-suited for homes with limited interior space or for replacement of existing outdoor water heating systems. The gray exterior finish is designed to blend unobtrusively with most home exteriors while withstanding exposure to the elements. For homeowners seeking a robust, high-capacity outdoor tankless solution that delivers consistent performance year-round, the FOGATTI Comfort 180S offers exceptional value and reliability.
#4 ThermoMate 102,000 BTU Natural Gas Tankless Water Heater
The ThermoMate Natural Gas Tankless Water Heater strikes an excellent balance between performance and efficiency, making it a strong contender for medium-sized households. With a 4.7 GPM flow rate and 102,000 BTU heating capacity, this indoor unit can comfortably service 3-4 fixtures simultaneously, providing enough hot water for a family’s typical daily needs without any waiting time or temperature fluctuations.
What truly distinguishes this model is its advanced temperature stability technology. The built-in chip adjusts heating power an impressive 20,000 times per second, ensuring hot water temperature remains within ±1°F of your setting. This precision means you’ll enjoy consistent shower temperatures without the sudden cold or hot bursts that can plague less sophisticated systems.
The ThermoMate’s heat exchanger is crafted from premium oxygen-free copper, which offers superior thermal conductivity and corrosion resistance compared to the stainless steel used in many competing models. This material choice results in a remarkable 98% thermal efficiency (versus approximately 80% for stainless steel models) and a Uniform Energy Factor (UEF) of 0.81. These efficiency ratings translate to approximately 30% lower operating costs compared to traditional tank systems.
Safety features abound in this thoughtfully designed unit, including comprehensive protections against boil-dry conditions, freezing, flame-outs, overheating, pipe blockage, excessive air pressure, and more. This extensive safety suite provides peace of mind and protects both your investment and your home from potential hazards associated with water heating.
Installation requires proper gas line sizing and adequate ventilation, but once in place, the ThermoMate provides reliable on-demand hot water with minimal maintenance requirements. For households seeking a balance of performance, efficiency, and advanced safety features in a mid-capacity tankless water heater, the ThermoMate delivers exceptional value and reliable operation.
#5 Ranein Natural Gas Tankless Water Heater For Small Households
The Ranein Natural Gas Tankless Water Heater is an excellent entry-level option for smaller households or those with modest hot water requirements. With an 80,000 BTU heating capacity and 3.6 GPM flow rate, this compact indoor unit is perfectly sized to support 2-3 water supply points—typically sufficient for a bathroom, kitchen, and bar area in apartments, condos, or smaller homes.
Unlike traditional tank water heaters that require substantial preheating time, the Ranein delivers hot water on demand with zero waiting time. This instant availability eliminates the familiar 30-minute wait for a tank to reheat after depletion, ensuring that hot water is always available when needed without planning ahead or staggering usage.
One of the most user-friendly features of this model is its four pre-programmed temperature modes designed for specific uses. The Dish mode (100°F) provides ideal temperature for washing dishes without scalding hands, while the Fruit mode (95°F) offers gentle cleaning for produce. For personal use, the Elderly mode (104°F) delivers a safe, comfortable temperature for sensitive skin, and the Infant mode (107°F) provides appropriate warmth for bathing children. These preset options simplify operation and enhance safety for various household members.
The compact design makes this unit particularly suitable for homes with limited installation space. As an indoor unit, proper venting is required, but the small footprint means it can fit in tight utility closets or other compact spaces where a traditional tank would be impractical.
While the Ranein doesn’t offer the high flow rates of premium models, its focused design provides reliable performance for smaller households or as a point-of-use heater for specific areas of larger homes. For singles, couples, or small families with modest hot water needs, this affordable tankless option delivers continuous hot water without the expense of oversized systems designed for larger households.
Comprehensive Buying Guide For Gas Tankless Water Heaters
Understanding Flow Rate Requirements
The flow rate, measured in gallons per minute (GPM), is perhaps the most critical specification to consider when selecting a gas tankless water heater. This number indicates how much hot water the unit can produce simultaneously. To determine your household’s needs, add up the typical GPM requirements of fixtures you might use at once:
- Shower: 1.5-2.5 GPM
- Bathroom faucet: 0.5-1.5 GPM
- Kitchen faucet: 1.0-2.0 GPM
- Dishwasher: 1.0-2.5 GPM
- Washing machine: 1.5-3.0 GPM
For example, if you regularly run a shower (2.0 GPM) and kitchen faucet (1.5 GPM) simultaneously, you’ll need a unit rated for at least 3.5 GPM. Larger households with multiple bathrooms should consider models with higher flow rates of 8-11 GPM to accommodate concurrent usage without temperature fluctuations.
BTU Rating And Heating Power
The BTU (British Thermal Unit) rating indicates the heating power of the tankless unit. Higher BTU ratings translate to greater heating capacity and ability to handle colder incoming water temperatures. For homes in northern climates where groundwater temperatures can be significantly lower, a higher BTU rating becomes especially important to maintain adequate flow rates.
Entry-level models typically offer 80,000-100,000 BTUs, which works well for small households or warmer climates. Mid-range units provide 120,000-150,000 BTUs, suitable for most average-sized homes. Premium models deliver 180,000-199,000 BTUs, capable of handling the most demanding applications even in colder regions.
Installation Considerations: Indoor vs. Outdoor
Gas tankless water heaters require proper venting to remove combustion gases safely. When choosing between indoor and outdoor models, consider:
- Indoor installation: Requires dedicated venting (typically with special stainless steel venting materials), adequate clearances around the unit, and possibly gas line upgrades. Protects the unit from weather elements and freezing temperatures.
- Outdoor installation: Eliminates the need for complex venting systems, saving on installation costs. Requires freeze protection in colder climates and weather-resistant construction. May need longer hot water delivery pipes, which can cause slight delays in hot water arrival at fixtures.
Some models, like the Rinnai RX199iN, offer the flexibility of either indoor or outdoor installation, providing more options depending on your home’s layout and restrictions.
Energy Efficiency And Operating Costs
Look for the Uniform Energy Factor (UEF) rating when comparing models—higher UEF ratings indicate better efficiency. Standard models typically have UEF ratings of 0.80-0.85, while condensing models can reach 0.92-0.98, capturing additional heat from exhaust gases to maximize efficiency.
While tankless units generally cost more upfront than traditional tanks, their longer lifespan (15-20 years versus 8-12 for tanks) and energy savings of 30-40% on water heating costs make them more economical over time. Condensing units cost more initially but provide greater efficiency and lower operating costs, particularly beneficial for households with high hot water usage.
Gas Supply Requirements
Many homeowners overlook the importance of adequate gas supply when installing a tankless water heater. These units require a significantly higher gas input than traditional tank water heaters—often 2-3 times more—but for shorter durations. Before purchasing, verify:
- Gas meter capacity (whether it can deliver the required BTUs)
- Gas line size (may need upgrading from ½” to ¾” or even 1″ depending on length of run and BTU requirements)
- Gas pressure at the appliance (typically 7″ w.c. for natural gas units)
Inadequate gas supply is a common cause of performance problems with tankless systems, resulting in inconsistent heating or inability to reach desired temperatures. A professional assessment before purchase can prevent costly modifications or disappointment with performance.
Maintenance Requirements
To maintain optimal performance and longevity, gas tankless water heaters require regular maintenance, particularly in areas with hard water. Annual descaling to remove mineral buildup in the heat exchanger is essential. Some models, like the Rinnai RX199iN with its Quick Flush feature, simplify this process.
Consider installing a water softener or scale inhibitor system if your area has very hard water, as this can significantly extend the life of your tankless unit and maintain its efficiency. Additionally, most manufacturers recommend annual inspection of venting systems, burners, and electronic components to ensure safe operation.
Advanced Features Worth Considering
Modern gas tankless water heaters offer various features that enhance convenience, safety, and performance:
- Wi-Fi connectivity: Allows remote temperature adjustment and monitoring via smartphone apps
- Recirculation pumps: Reduce wait time for hot water at distant fixtures
- Scale detection: Alerts you when maintenance is needed
- Freeze protection: Essential for units installed in unheated spaces or outdoor models in colder climates
- Preset temperature modes: Simplify operation for different uses like bathing children or washing dishes
- Condensate neutralizers: Required for condensing units to prevent acidic condensate from damaging plumbing
While these features add to the initial cost, they can significantly improve the user experience and protect your investment over the unit’s lifespan.
Compatibility With Home Size And Climate
Climate plays a crucial role in determining the appropriate size and type of tankless water heater. In colder northern regions where groundwater temperatures can drop below 40°F in winter, you’ll need a more powerful unit with higher BTU output to achieve the same flow rate compared to warmer southern regions where incoming water might be 60°F or higher.
A general guideline is that for every 10°F drop in incoming water temperature, you need about 1 additional GPM of capacity to maintain the same performance. When sizing your unit, consider your region’s coldest groundwater temperatures to ensure adequate performance year-round.
