If you want efficient, space-saving hot water with lower emissions, low NOx condensing tankless water heaters are a smart place to start. They deliver continuous hot water while helping reduce wasted energy.
Below, we focus on models that balance flow rate, fuel flexibility, and installation needs so you can match the right heater to your home or business.
Best 10 Low Nox Condensing Tankless Water Heaters Picks for 2026
Whole-Home Flexibility
Rinnai RX199iN 11.1 GPM Condensing Smart Sense
- Indoor or outdoor installation flexibility
- Runs on natural gas or propane
- Up to 11.1 GPM with UEF .98
Best For: Larger homes wanting high capacity and install flexibility
Ultra-Low NOx Smart Control
Rheem IKONIC 11.2 GPM LP Condensing
- Ultra-low NOx burner for lower emissions
- Built-in EcoNet Wi-Fi controls
- Compact, high-output propane unit
Best For: Propane households wanting smart control and low emissions
Commercial Recirculation Pick
Rinnai CU160iN 9 GPM Natural Gas
- Commercial-grade tankless design
- Circ-Logic recirculation support
- Wi-Fi monitoring for convenience
Best For: Businesses needing efficient on-demand hot water
High-Efficiency Budget-Friendly Pick
Rheem RTGH 6.8 GPM Ultra-Low NOx
- 6.8 GPM for whole-house use
- Ultra-low NOx and 0.93 UEF
- Digital control with freeze protection
Best For: Large families wanting efficient indoor propane hot water
High-Efficiency Indoor Pick
Noritz NRC66DVNG 6.6 GPM Natural Gas
- 6.6 GPM output for steady hot water
- Low-NOx condensing indoor design
- PVC venting support and remote thermostat included
Best For: Indoor natural-gas installs that want efficient, compact tankless hot water
Commercial Flex Choice
Rinnai CX199iN 199,000 BTU Condensing Heater
- Up to 11.1 GPM for high hot-water demand
- Indoor or outdoor install with Versa Vent
- Supports natural gas or propane with Smart-Circ recirculation
Best For: Large-demand installs needing flexible placement and smart recirculation
Recirculation Value Pick
Rheem Prestige RTGH-RH11DVLN 11.0 GPM
- 11 GPM output with built-in recirculation
- High-efficiency condensing design with .94 UEF
- Leak detection and auto-learn programming
Best For: Indoor natural-gas replacements that prioritize comfort and efficiency
Compact 2-3 Bath Saver
- 5.1 GPM for 2–3 bathrooms
- Condensing design helps cut gas use
- Touchscreen with safety protections
Best For: Families wanting a space-saving indoor natural gas tankless heater
Ultra-Low NOx Whole-Home High Flow
Ultra-Low NOx Whole-Home High Flow
- 10.1 GPM for whole-house demand
- Ultra-low NOx condensing efficiency
- Wi‑Fi control with maintenance alerts
Best For: Large households needing high flow and remote control
Efficient Dual Heat Exchange Performer
Efficient Dual Heat Exchange Performer
- 0.86 UEF condensing efficiency
- 5.28 GPM for multi-point use
- LED touchscreen with 8 safety protections
Best For: Homes wanting a compact, efficient indoor gas unit for everyday use
Whole-Home Flexibility – Rinnai RX199iN 11.1 GPM Condensing Smart Sense
If you’re comparing low nox condensing tankless water heaters for a high-demand home, the Rinnai RX199iN stands out for its flexibility and strong output. It can be installed indoors or outdoors, runs on natural gas or propane, and delivers up to 11.1 GPM for whole-house hot water needs.
Best For: Homes that want a high-capacity tankless unit with indoor/outdoor installation flexibility.
Pros:
- Indoor or outdoor installation options with Versa Vent support
- Smart Sense gas control works with natural gas or propane
- Up to 11.1 GPM can support multiple fixtures at once
- UEF .98 and Quick Flush feature add efficiency and easier maintenance
Cons:
- Outdoor installation requires the RX-OVC vent cap
- Professional installation is recommended
- Wi-Fi control needs the separate Controlr module
Overall, this model is a strong fit if you want a space-saving tankless unit with broad installation flexibility and high efficiency. Its capacity and fuel versatility make it especially practical for larger households.
Ultra-Low NOx Smart Control – Rheem IKONIC 11.2 GPM LP Condensing
For shoppers focused on low nox condensing tankless water heaters, the Rheem IKONIC combines strong whole-home performance with an ultra-low NOx burner and built-in Wi-Fi. It delivers up to 11.2 GPM on liquid propane and is designed for compact installation flexibility.
Best For: Propane-powered homes that want connected controls and ultra-low NOx operation.
Pros:
- Ultra-low NOx burner helps reduce greenhouse gas NOx emissions
- Built-in EcoNet Wi-Fi for monitoring, alerts, and temperature control
- Up to 11.2 GPM supports multiple simultaneous uses
- Compact design with quick hang bracket and side clearance advantages
Cons:
- Liquid propane only
- Outdoor use requires an outdoor conversion kit
- Professional installation is the safer choice for setup
This is a solid pick if you want a high-efficiency propane tankless unit with smart controls and low-emission design. It balances convenience, compact sizing, and whole-house output well.
Commercial Recirculation Pick – Rinnai CU160iN 9 GPM Natural Gas
Rinnai CU160iN Commercial Natural Gas Condensing Tankless Water Heater, Indoor Installation, 9 GPM
Check Price On AmazonThe Rinnai CU160iN is aimed at commercial spaces that need dependable low nox condensing tankless water heaters with efficient operation and recirculation support. With indoor installation and a 9 GPM flow rate, it’s built for businesses that want consistent hot water on demand.
Best For: Commercial applications that need a compact natural-gas tankless heater with Wi-Fi monitoring.
Pros:
- Commercial-grade design with space-saving tankless construction
- 9 GPM flow rate for steady business hot water demand
- Circ-Logic recirculation patterns help match usage habits
- Wi-Fi monitoring adds convenient system visibility
Cons:
- Indoor installation only
- Professional installation is recommended
- Lower flow than some larger residential whole-home units
In a commercial setting, this model makes sense when you value efficient on-demand heating and recirculation control over maximum flow. It’s a practical choice for businesses wanting dependable performance in a compact footprint.
High-Efficiency Budget-Friendly Pick – Rheem RTGH 6.8 GPM Ultra-Low NOx
If you want low nox condensing tankless water heaters for a large family home, the Rheem RTGH-68DVLP-3 offers strong efficiency in a simpler indoor package. It provides up to 6.8 GPM, ultra-low NOx emissions compliance, and direct-vent indoor installation.
Best For: Large households that want efficient propane tankless hot water with straightforward controls.
Pros:
- Up to 6.8 GPM supports 2-3 simultaneous showers
- Ultra-low NOx emissions compliant
- 0.93 UEF and super high efficiency help reduce gas use
- Digital LED temperature control with ±1°F precision
Cons:
- Indoor installation only
- Liquid propane powered
- Professional installation is recommended
This heater is a good fit when efficiency and practical whole-house performance matter more than premium extras. Its combination of high efficiency, safety features, and dependable flow makes it a well-rounded propane option.
High-Efficiency Indoor Pick – Noritz NRC66DVNG 6.6 GPM Natural Gas
Noritz NRC66DVNG Indoor Condensing Direct Tankless Hot Water Heater, 6.6 GPM - Natural Gas
Check Price On AmazonIf you want one of the more straightforward low nox condensing tankless water heaters for a natural gas setup, the Noritz NRC66DVNG is built around continuous hot water and efficient indoor operation. It supports Schedule 40 PVC venting, includes a remote thermostat and 6′ power cord, and is sized for wall mounting in a compact footprint.
Best For: Homeowners who want an indoor, high-efficiency tankless unit with simple PVC venting and strong output for everyday hot water demand.
Pros:
- 6.6 GPM flow rate for steady whole-home hot water delivery
- High-efficiency, low-NOx condensing design
- Can be vented with Schedule 40 PVC pipe and fittings
- Remote thermostat and 6′ power cord included
Cons:
- Natural gas only, so it is not a dual-fuel option
- Indoor installation requires proper venting setup
- Max temperature is listed at 140°F
For buyers focused on practical indoor installation and efficient operation, this Noritz model covers the core needs well. Its combination of low-NOx condensing performance, compact wall-mount form, and included controls makes it a solid fit for replacing older hot water equipment.
Commercial Flex Choice – Rinnai CX199iN 199,000 BTU Condensing Heater
The Rinnai CX199iN stands out among low nox condensing tankless water heaters because it is designed for flexible installation and high hot-water output. It can be installed indoors or outdoors with Versa Vent, supports either natural gas or propane through Smart Sense gas control, and delivers up to 11.1 GPM for larger demand.
Best For: Larger homes or commercial settings that need a high-capacity, flexible gas tankless water heater with smart circulation features.
Pros:
- Up to 11.1 GPM for high-demand applications
- Indoor or outdoor installation flexibility with Versa Vent
- Supports natural gas or propane with Smart Sense gas control
- Includes internal pump and Smart-Circ recirculation technology
Cons:
- Outdoor installation requires the RX-OVC vent cap
- WiFi control requires the Controlr module, which is not included
- Professional installation is recommended
This model is a strong fit when versatility matters as much as capacity. Its condensing efficiency, commercial-grade output, and built-in recirculation features make it a practical upgrade for users who need more than a basic tankless heater.
Recirculation Value Pick – Rheem Prestige RTGH-RH11DVLN 11.0 GPM
For shoppers comparing low nox condensing tankless water heaters, the Rheem Prestige RTGH-RH11DVLN is appealing because it combines high efficiency with built-in recirculation. It is an indoor natural gas model with a compact, tank-replacement-friendly design, plus water and gas leak detection for added protection.
Best For: Buyers who want fast hot water delivery, built-in recirculation, and an efficient indoor tankless replacement.
Pros:
- 11 GPM flow rate supports broad household demand
- Built-in recirculation helps reduce wait time for hot water
- High-efficiency condensing design with .94 UEF
- Leak detection can shut down the unit and show an error code
Cons:
- Indoor natural gas only
- Floor-mount style may not suit every installation plan
- Recirculation and smart features add complexity versus a basic unit
This Rheem model is a practical choice when comfort and efficiency both matter. Its combination of recirculation, leak detection, and compact sizing makes it a strong candidate for replacing an older tank-style heater.
Compact 2-3 Bath Saver – Compact 2-3 Bath Saver
If you’re comparing low nox condensing tankless water heaters for a smaller home, the Ranein is built around steady hot water, strong efficiency, and a compact wall-mounted footprint. It delivers on-demand flow for everyday family use while using condensing tech to recycle exhaust heat and help reduce gas consumption.
Best For: Households needing an indoor natural gas tankless unit for 2–3 bathrooms with space-saving installation.
Pros:
- 5.1 GPM and 120,000 BTU output support multiple fixtures at once.
- Condensing design and 4-stage modulation are aimed at lower gas usage.
- Smart touchscreen offers precise temperature control and built-in diagnostics.
- Includes anti-freeze protection, safety shutoffs, vent pipe, and condensate drain line.
Cons:
- Professional installation is recommended.
- Not recommended for elevations above 2,000 ft.
- Lower flow than larger whole-home units if demand is very high.
Overall, this is a practical pick if you want a compact condensing tankless heater with modern controls and enough output for typical family routines. It balances efficiency, safety features, and a fairly complete installation kit.
Ultra-Low NOx Whole-Home High Flow – Ultra-Low NOx Whole-Home High Flow
For shoppers focused on low nox condensing tankless water heaters with strong whole-house output, the Rheem IKONIC stands out for its 10.1 GPM capacity and super high efficiency design. It’s aimed at homes that need continuous hot water for multiple simultaneous uses, plus smart remote control through built-in Wi‑Fi.
Best For: Larger homes that want a high-flow condensing unit with Wi‑Fi controls and flexible installation.
Pros:
- 10.1 GPM and 180,000 BTUs support multiple applications at once.
- Condensing ultra-low NOx design is built for high efficiency and lower emissions.
- EcoNet Wi‑Fi lets you adjust settings, track usage, and receive maintenance alerts.
- Compact form factor includes quick hang bracket and outdoor conversion capability.
Cons:
- More expensive and more complex than smaller basic units.
- Rated maximum temperature is 140°F.
- Outdoor setup requires a separate conversion kit.
This is a strong choice if your priority is whole-home performance rather than a smaller, budget-focused heater. The combination of high flow, Wi‑Fi control, and compact mounting flexibility makes it especially appealing for busy households.
Efficient Dual Heat Exchange Performer – Efficient Dual Heat Exchange Performer
If you’re shopping low nox condensing tankless water heaters for dependable everyday hot water, the ThermoMate offers a balanced mix of efficiency, compact size, and safety features. Its dual heat exchanger design is intended to recover waste heat efficiently while maintaining steady output for bathrooms and other residential points of use.
Best For: Residential buyers who want a compact, efficient natural gas tankless heater for showers and multi-point use.
Pros:
- 0.86 UEF efficiency and condensing design are geared toward lower energy use.
- 5.28 GPM and 114,000 BTU support two showers simultaneously under stated conditions.
- Dual heat exchanger construction combines stainless steel and copper components.
- LED touchscreen, error-code display, and multiple safety protections add convenience.
Cons:
- Condensate must be drained, and a neutralizer kit is recommended but not included.
- Flow capacity is lower than larger whole-home premium models.
- Indoor install requires standard gas, venting, and electrical setup.
As a result, this model fits buyers who want efficient performance without jumping to a much larger unit. The compact cabinet, clear diagnostics, and broad protection list make it an easy fit for many residential installs.
How We Picked the Best Low Nox Condensing Tankless Water Heaters
We focused on Low Nox Condensing Tankless Water Heaters with strong efficiency ratings, practical flow rates, and enough heating capacity for real-world use. We also favored models with indoor-installation options, fuel flexibility, and features that matter to buyers, such as recirculation support, commercial-grade output, and simple control systems.
Quick Comparison
For large households, higher-BTU models with 9 to 11+ GPM are the best fit because they can handle multiple showers and appliances at once. Mid-range units around 6 to 7 GPM work well for smaller homes, apartments, or single-zone usage. Commercial buyers should look for higher output and durability rather than just headline efficiency.
Key Buying Factors for Low Nox Condensing Tankless Water Heaters
Flow Rate and Peak Demand
GPM tells you how much hot water the unit can produce at a time. Add up the fixtures you expect to run simultaneously, then choose a heater with some extra capacity. Undersizing is the most common mistake buyers make.
Fuel Type and Venting
Most Low Nox Condensing Tankless Water Heaters are gas-powered, but not all support the same fuel. Check whether you need natural gas or propane, and confirm the venting requirements before buying. Condensing units usually need specific exhaust setups, so installation planning matters.
Efficiency and Temperature Control
Higher efficiency can lower operating costs over time, especially in homes with frequent hot-water use. Strong temperature stability is also important if you want consistent showers, laundry cycles, and dishwasher performance.
Indoor Installation, Recirculation, and Controls
Indoor models are common in this category, but they require adequate clearances and proper venting. Built-in recirculation can improve convenience by reducing wait times for hot water. Smart controls, leak protection, and freeze protection can add value depending on your climate and usage pattern.
Who Should Buy Which Low Nox Condensing Tankless Water Heaters?
Choose a high-output model if you have a large family, multiple bathrooms, or a commercial application. Pick a mid-size unit if you want efficient performance for a smaller home without overbuying capacity. If hot water convenience matters most, look for built-in recirculation and smart controls. For propane users, verify fuel compatibility first so you do not narrow your options later.
In short, the best Low Nox Condensing Tankless Water Heaters are the ones that match your fuel, flow demand, and installation setup—not just the highest BTU number.
