Rinnai or A. O. Smith? Tankless Water Heaters Compared in 2026
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When you search for rinnai vs a o smith tankless water heater options, you will find two strong contenders. Both units use condensing technology for high efficiency and provide endless hot water. The Rinnai RX199iN offers dual-fuel capability and indoor or outdoor installation. The A. O. Smith 540H is designed strictly for outdoor use and runs on natural gas only. This guide compares their specs to help you choose.
Key differences
| Aspect | Rinnai 11.1 GPM Condensing Dual-Fuel Water Heater | A. O. Smith 10 GPM Outdoor Condensing Tankless Heater |
|---|---|---|
| Flow Rate | 11.1 GPM | 10.0 GPM |
| Fuel Type | Propane or Natural Gas | Natural Gas |
| Installation Location | Indoor/Outdoor | Outdoor |
| UEF | .98 | .94 |
| Heat Exchanger Material | not listed | Copper |
Which one should you choose?
Choose Rinnai 11.1 GPM Condensing Dual-Fuel Water Heater if
- You need a higher flow rate for multiple fixtures.
- You want the option to use propane or natural gas.
- You plan to install the unit indoors or outdoors.
Choose A. O. Smith 10 GPM Outdoor Condensing Tankless Heater if
- You prefer a dedicated outdoor installation.
- You value a copper heat exchanger for heat transfer.
- You are using natural gas only.
Verdict: The Rinnai RX199iN is the better choice if you need flexibility in fuel type, location, and higher flow rates. The A. O. Smith 540H suits those who only need natural gas and prefer a dedicated outdoor setup with a copper heat exchanger. Your decision depends on your specific fuel availability and installation constraints.
Rinnai RX199iN vs A. O. Smith 540H
Flow rate capacity
The Rinnai RX199iN delivers a maximum flow rate of 11.1 gallons per minute. This capacity supports up to seven fixtures running simultaneously. You get more hot water volume compared to the A. O. Smith 540H, which provides 10.0 gallons per minute. The A. O. Smith unit is rated for a three-bath home in northern climates or a four-bath home in southern regions. While both units provide endless hot water, the Rinnai model has a higher peak output. This extra gallon per minute can be useful for larger households with simultaneous demand.
Fuel flexibility
The Rinnai RX199iN features a Smart Sense gas control system that allows it to run on either propane or natural gas. This dual-fuel capability gives you more options for fuel sources. The A. O. Smith 540H is designed specifically for natural gas only. If you have propane tanks or anticipate switching fuel types, the Rinnai offers greater versatility. The A. O. Smith unit locks you into natural gas infrastructure. For homes without natural gas lines, the Rinnai is the only viable choice between these two specific models.
Installation location
The Rinnai RX199iN is rated for both indoor and outdoor installation. This versatility allows you to place the unit in a basement, garage, or exterior wall. The A. O. Smith 540H is designed for outdoor use only. It features a direct vent design suitable for exterior mounting. If you have limited exterior space or prefer to hide the unit indoors, the Rinnai provides the necessary flexibility. The A. O. Smith unit restricts you to outdoor placement, which may limit where you can install the heater in your home.
Energy efficiency
Both units use condensing technology to achieve high efficiency. The Rinnai RX199iN has a Uniform Energy Factor (UEF) of .98. The A. O. Smith 540H has a UEF of .94. Both are Energy Star certified. The Rinnai model achieves a slightly higher efficiency rating. This difference means the Rinnai converts a higher percentage of fuel into hot water. While both are efficient, the Rinnai edge is small but present. You will see marginal savings in fuel costs with the Rinnai over time due to this higher efficiency score.
Physical dimensions
The Rinnai RX199iN measures 30.1 inches in height, 18.5 inches in width, and 30.1 inches in length. It weighs 55 pounds. The A. O. Smith 540H is more compact, measuring 23.6 inches in height, 17.8 inches in width, and 17.8 inches in length. It weighs 59 pounds. The A. O. Smith unit has a smaller footprint, which may fit better in tight spaces. However, it is slightly heavier. The Rinnai is taller and wider but lighter. Consider your available space when choosing between the rectangular Rinnai and the more square A. O. Smith form factor.
Which tankless heater fits your home
Large homes needing max flow
The Rinnai RX199iN delivers 11.1 GPM, supporting seven fixtures at once. Its dual-fuel Smart Sense system works with propane or natural gas. This flexibility allows indoor or outdoor placement. You get higher volume output for large households with multiple simultaneous demands.
Outdoor installs with compact space
The A. O. Smith 540H is designed for outdoor direct venting. It measures 17.8 by 17.8 inches, fitting tighter spaces. The unit includes a wall mount temperature remote. Its compact footprint and dedicated outdoor design simplify installation where indoor venting is difficult.
Users valuing heat transfer speed
A. O. Smith uses a commercial-grade copper heat exchanger. This material offers 25 times better heat transfer than steel. You benefit from stable water temperatures and efficient heating. The condensing technology ensures high efficiency while maintaining consistent performance during use.
Flexible fuel and venting needs
Rinnai’s Versa Vent and Smart Sense gas control allow versatile installation. You can choose between propane or natural gas sources. The unit supports indoor or outdoor mounting with the right vent cap. This adaptability suits varied home layouts and fuel availability.
The products compared
Rinnai 11.1 GPM Condensing Dual-Fuel Water Heater
Best for: High-flow residential needs
- Fuel Type
- Natural Gas or Propane
- Flow Rate
- 11.1 GPM
- BTU
- 199k BTU
- Installation Location
- Indoor/Outdoor
- Venting Type
- Condensing
- Dimensions
- 30.1 × 18.5 × 30.1 inches
View on Amazon: Rinnai 11.1 GPM Condensing Dual-Fuel Water Heater Affiliate link
The Rinnai RX199iN is a condensing tankless water heater delivering 11.1 GPM of hot water. It runs on natural gas or propane and works indoors or outdoors. The unit measures 30.1 by 18.5 by 30.1 inches and weighs 55 pounds. It features a high energy efficiency factor of 0.98. This model suits homes needing high flow rates from a compact, versatile unit.
Pros
- Delivers 11.1 GPM flow rate
- Condensing design for 0.98 UEF efficiency
- Indoor and outdoor installation options
- Runs on propane or natural gas
Cons
- WiFi control module sold separately
- Requires professional installation
- Labor warranty drops to one year if not registered within 90 days
Good fit if
- You need a high-flow unit for multiple fixtures
- You want indoor or outdoor flexibility
- You prefer propane or natural gas fuel
Skip if
- You want built-in WiFi without extra purchases
- You prefer a DIY installation process
- You need a smaller footprint than 30 inches
Verdict: Rinnai RX199iN 11.1 GPM Condensing provides strong performance for large households. It fits homes that need high hot water output and flexible placement options.
A. O. Smith 10 GPM Outdoor Condensing Tankless Heater
Best for: large households with outdoor space
- Fuel Type
- Natural Gas
- Flow Rate
- 10.0 GPM
- BTU
- 199,000 BTU/hr
- Installation Location
- Outdoor
- Dimensions
- 23.6 x 17.8 x 17.8 inches
- Venting Type
- Condensing
View on Amazon: A. O. Smith 10 GPM Outdoor Condensing Tankless Heater Affiliate link
This outdoor unit delivers 10.0 GPM at 199,000 BTU using natural gas. It features a commercial-grade copper heat exchanger for efficient heat transfer and condensing technology that achieves a .94 UEF. The design supports direct venting up to 100 feet and includes a wall mount temperature remote. It suits homes with up to four bathrooms in southern climates or three in northern regions.
Pros
- Delivers up to 10.0 GPM flow rate
- 199,000 BTU/hr heating capacity
- Commercial-grade copper heat exchanger
- Includes wall mount temperature remote controller
- Supports venting up to 100 feet
Cons
- Outdoor installation only
- Professional installation recommended
- No smart app integration listed
Good fit if
- You need high flow for multiple bathrooms
- You have outdoor space for installation
- You use natural gas fuel
Skip if
- You require indoor installation
- You need propane fuel
- You want smart home connectivity
Verdict: A. O. Smith 10 GPM Outdoor Gas Heater offers robust performance for large households with outdoor space. It is best for users prioritizing flow rate and durability over smart features.
Specifications side by side
| Spec | Rinnai 11.1 GPM Condensing Dual-Fuel Water Heater | A. O. Smith 10 GPM Outdoor Condensing Tankless Heater |
|---|---|---|
| Fuel Type | Natural Gas or Propane | Natural Gas |
| Flow Rate | 11.1 GPM | 10.0 GPM |
| BTU | 199k BTU | 199,000 BTU/hr |
| Installation Location | Indoor/Outdoor | Outdoor |
| Dimensions | not stated | 23.6 x 17.8 x 17.8 inches |
| Venting Type | Condensing | Condensing |
| Weight | 55 pounds | 59 pounds |
| Size | 11.1 GPM | not stated |
| Color | Silver | White |
| Model | RX199iN | ATO-540H-N 100 |
Frequently asked questions
Can the Rinnai RX199iN run on propane?
Yes, the Rinnai RX199iN is a dual-fuel unit. It operates on both natural gas and propane. This flexibility allows you to choose your preferred fuel source based on availability. You do not need to commit to a single gas type for installation.
Is the A. O. Smith heater safe for outdoor use?
Yes, the A. O. Smith ATO-540H-N 100 is designed for outdoor installation. Its condensing technology and build quality suit exterior placement. You can install it outside without needing a vented indoor space. This saves indoor square footage for other uses.
Which unit provides more hot water flow?
The Rinnai RX199iN provides a higher flow rate of 11.1 GPM. The A. O. Smith model delivers 10 GPM. If you need to run multiple fixtures simultaneously, the Rinnai unit offers greater capacity. This supports up to seven fixtures at once.
Do both heaters use condensing technology?
Yes, both the Rinnai RX199iN and the A. O. Smith ATO-540H-N 100 use condensing venting. This technology captures heat from exhaust gases to improve efficiency. You get higher energy efficiency ratings compared to standard non-condensing units.
How do the sizes compare for installation?
The Rinnai RX199iN measures 18.5 inches wide and 30.1 inches high. The A. O. Smith unit is slightly narrower at 17.8 inches wide and 23.6 inches high. Consider your available wall space when choosing between the two models for installation.
Which heater is lighter to mount?
The Rinnai RX199iN weighs 55 pounds. The A. O. Smith ATO-540H-N 100 weighs 59 pounds. The Rinnai unit is slightly lighter. This minor difference may simplify handling during the installation process for your mounting team.