Buying a condensing tankless water heater means prioritizing efficiency, space savings, and reliable hot water on demand. This guide highlights five top options and explains who each model best serves. The top picks balance compact size, high gas input flexibility (natural gas or propane), and smart features to help homes remain comfortable with lower energy use. Ideal buyers include large families needing steady hot water, and homeowners seeking indoor/outdoor versatility and smart control.
Quick Product Snapshot
| Product | Max GPM | BTU | Best For |
|---|---|---|---|
| NEW Rinnai RX199iN | 11.1 | 199,000 | Large households; indoor/outdoor versatility |
| ThermoMate CZ480NG | 5.28 | 114,000 | Small to mid-size homes; economical option |
| NEW Rinnai RXP199iN | 11.1 | 199,000 | Similar high-demand setups; built-in efficiency |
| NEW Rinnai RX130iN | 7.1 | 130,000 | Mid-size households; space-conscious |
| Westinghouse Smart Tankless | 7.9 | 180,000 | Whole-home performance; WiFi control |
Rinnai RX199iN Condensing Tankless Water Heater
The RX199iN is a high-capacity, condensing tankless unit suitable for indoor or outdoor installation with Versa Vent. It supports natural gas or propane, delivering up to 11.1 GPM and 199,000 BTU. A Smart Sense gas control system drives efficient operation, with a Quick Flush feature for maintenance and a high energy efficiency factor (UEF .98). Best for large families or homes with multiple simultaneous hot-water needs. Caution: outdoor use requires the RX-OVC vent cap for proper venting.
- Best for: large households and versatile installation
- Why selected: top GPM and flexible venting options
- Limitation: control module for WiFi is not included
ThermoMate CZ480NG Condensing Tankless Water Heater
The CZ480NG offers 5.28 GPM with a 114,000 BTU input and a 0.86 UEF efficiency. Its dual heat exchanger design captures and recycles waste heat to maximize energy savings. It’s well suited for households that need reliable, on-demand hot water without excessive capacity. Best for mid-size homes seeking efficient performance at a lower upfront footprint. Caution: flow can decrease with very cold inlet water temperatures.
- Best for: mid-size homes and energy-conscious buyers
- Why selected: dual heat exchangers improve heat recovery
- Limitation: lower max GPM compared to larger units
NEW Rinnai RXP199iN Smart Sense Condensing Tankless Water Heater
The RXP199iN matches the RX199iN in size and capability, offering 11.1 GPM and 199,000 BTU with indoor/outdoor installation and Smart Sense control. Its compact form provides robust hot-water delivery for busy households, with a Quick Flush feature for simple maintenance. Best for: homes requiring both high capacity and flexible placement. Caution: WiFi control module is sold separately.
- Best for: high-demand setups with outdoor/indoor needs
- Why selected: identical high flow with added modern controls
- Limitation: control module not included
NEW Rinnai RX160iN Condensing Tankless Water Heater
The RX160iN provides up to 9 GPM and 160,000 BTU with indoor/outdoor adaptability. It features the Versa Vent system for versatile installation and a high UEF rating of .97. Best for mid-to-large homes that want reliable hot water with a manageable size. Caution: slightly lower maximum GPM than the biggest RX models.
- Best for: space-conscious homes needing solid performance
- Why selected: good balance of flow and size
- Limitation: not the highest GPM among condensing options
Rheem RTG-84XLN-3 Outdoor Tankless
The Rheem RTG-84XLN-3 outdoor unit delivers 8.4 GPM with 180,000 BTU. It’s engineered for outdoor installation and supports wall mounting by a qualified installer. Best for outdoor-only setup where space inside is limited. Caution: outdoor units require weatherproofing and proper venting.
- Best for: outdoor installations where internal space is limited
- Why selected: reliable outdoor performance with solid GPM
- Limitation: outdoor usage requires weatherproofing and proper mounting
MIZUDO Natural Gas Tankless Water Heater
The MIZUDO unit offers 10.3 GPM with 199,000 BTU and WiFi/app control. It is designed for large households with multiple simultaneous outlets and includes extensive safety features like freeze protection and anti-dry firing. Best for: large families seeking remote management. Caution: compatibility and app features depend on the model and region.
- Best for: large households needing remote control
- Why selected: high flow with smart connectivity
- Limitation: app functionality may vary by region
Buying Guide: Condensing Tankless Water Heaters
What to consider when choosing
Flow rate (GPM) should match peak hot-water demand. Condensing units recover waste heat for higher efficiency, typically improving energy savings over non-condensing models. Consider venting requirements, installation flexibility (indoor vs outdoor), and fuel type compatibility (propane or natural gas).
Size and installation location affect space planning. Look for Versa Vent compatibility and whether a built-in recirculation pump is included or available as an add-on. WiFi or Controlr compatibility can simplify remote monitoring but may require additional hardware.
Energy efficiency and operating costs
Higher UEF ratings indicate better efficiency. Condensing designs capture and reuse waste heat, reducing energy consumption. For homes with high hot-water demand, prioritize units with GPM figures that exceed daily needs to prevent runaway heat fluctuations.
Durability and maintenance
Look for corrosion-resistant heat exchangers and protective protections against freezing, overheating, and flame-out. Regular flushing and maintenance features simplify long-term care and reduce the risk of mineral buildup in line with water hardness.
Installation and warranties
Indoor/outdoor versatility reduces location constraints, but outdoor installations require weatherproofing and proper venting. Certified installers should handle gas connections and venting for safety. Review warranty terms separately from the unit data sheet and ensure local codes permit the chosen setup.
FAQ
- What is a condensing tankless water heater? A tankless water heater that recycles exhaust heat to improve efficiency, delivering hot water on demand with lower energy use than non-condensing models.
- Is it better to choose gas or propane? Gas and propane options provide flexibility depending on your utility access. Choose based on availability, cost, and venting compatibility.
- How many fixtures can these units support? It depends on GPM and inlet water temperature. High-flow models (around 11 GPM) support multiple showers or fixtures simultaneously, while smaller units are better for modest demand.
- Do these units require professional installation? Yes. Gas connections, venting, and electrical considerations typically require a licensed installer to meet code and safety standards.
- Can I control these heaters remotely? Some models offer WiFi or Controlr modules for remote monitoring and adjustments, though some controls may be sold separately.
- What maintenance is needed? Periodic flushing and inspection help prevent mineral buildup and maintain efficiency. Look for Quick Flush features to simplify this task.