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AO Smith is an American company that manufactures residential and commercial water heating products.

AO Smith maintains a significant portion of the North American water heating market.

Founded in 1874, AO Smith has had over a century of developments and achievements. The company is currently headquartered at Milwaukee, Wisconsin.

AO Smith is one of the world’s leading producers of water heaters and boilers with sales and distribution in over 60 countries.

It is also the owner of the largest water heater factory in the world. The company is known for creating reliable, robust, efficient and durable products.

Products from AO Smith include natural gas, propane, electric, hybrid, solar, and tankless water heaters. Boilers, storage tanks, skid systems, pump tanks, and expansion tanks are also manufactured.

AO Smith Tankless Water Heater Reviews

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The tankless water heaters by AO Smith can be broadly classified into electric and gas-fired types.

There are several models under these types, which can be further categorized under various series based on the model features.

Let us take a look at these model series and their characteristics in the table given below.

Let us now discuss these characteristics and some other features of these tankless water heater series in detail.

AO Smith Gas-Fired Tankless Water Heaters Review

Non-Condensing Models

The non-condensing gas tankless water heaters consist of single heat exchangers for heating water. All the models under this series are available in two variations each for natural gas and propane as the fuel type.

A maximum flow rate of up to 10 GPM is available in this series.

The heat exchangers are made of commercial-grade copper. The units have low NOx emissions and adhere to the lead-free standards set by the authorities.

Another feature of this series is a built-in freeze protection system which is present in all units.

The indoor models are

  1. ATI-110
  2. ATI-310
  3. ATI-510

with maximum flow rates of 6.6 GPM, 8 GPM, and 10 GPM respectively. All these models come with remote control and power cords as included accessories.

4” Category III Vents are required for these units and they can be installed either horizontally or vertically.

The outdoor models are named as ATO-110, ATO-301, and ATO-510. The models come with a standard remote control feature. No venting is required for these models.


  • These units have several safety features to ensure secure heater operation.
  • The 510 models can be linked up to four units for increased output. This can be done without any additional accessories.
  • A 15-year warranty period is offered for all the units under this series.
  • These are fully modulating units that can be used for both residential and commercial applications.
  • Electronic ignition saves energy as opposed to a pilot light.


  • There are models with higher efficiencies available in the market.
  • Hot water temperature may drop if several hot water appliances are used at once.
  • Existing vents cannot be used. The venting requirements as described by the manufacturer must be provided.

Condensing Models

AO Smith ATIO-910-N Tankless Heater with Heavy Duty Commercial

These are high-efficiency eco-friendly models with ultra-low NOx emissions. These models are incorporated with condensing technology that uses dual-heat exchangers for maximum efficiency.

As a result, these units have a Uniform Energy Factor of 0.95 and low operating costs. Additionally, all the models under this category are Energy Star qualified.

The maximum flow rate available in this series id 10 GPM. All the models are available in two variations based on the fuel type.

The primary heat exchanger is made of high-tolerant commercial-grade copper and the secondary heat exchanger is made of stainless steel.

The indoor models in this series are –

  1. ATI-240,
  2. ATI-340
  3. ATI-540

with respective flow rates of 6.6 GPM, 8 GPM, and 10 GPM.

The indoor models are equipped with advanced diagnostics and simple temperature control.

Also, these models come with a factory-installed power cord. The exhaust gases are not very hot which allows for the use of PVC or CPVC vents.

The outdoor models – ATO-240, ATO-340, and ATO-540 have the same flow rates as their corresponding indoor models.

The units also have advanced diagnostics for simple error detection. Additionally, they have a wall-mount temperature controller that can be installed remotely.


  • Apart from the Easy-Link of the 540 models, they can also be Multi-Linked up to 20 units for very large demands.
  • A common vent for up to 8 units can be used.
  • Applicable for residential as well as commercial purposes.
  • A 15-year warranty period for residential applications is available.
  • These are highly efficient units that can help save money on energy bills.
  • Several safety features are incorporated into these units.


  • These units are expensive to buy and installation may also cost a significant amount of money.
  • There is some wait time between turning on a tap and delivery of hot water.

AO Smith Electric Tankless Water Heaters Review

Two Chamber Models

The single-chamber models of electric tankless water heaters from AO Smith are compact units that are ideal for point-of-use applications or small households.

The series that come under this type are the R2 and the C2 series. The R2 models are used for residential purposes and the C2 models are used for commercial applications.

The models under these series have dual heating chambers.

These models have a Uniform Energy Factor of 0.84 and an activation flow rate of 0.25 GPM. These are light-weight heaters that weigh less than 15 pounds. The maximum flow rate available in this series is 5.5 GPM.

The user interface is simple to understand and the temperature can be adjusted by simply pressing the increment or decrement buttons.

Another feature is the in-built scale reduction technology in these units that resist and reduce scale deposits in the chamber as well as the heating elements.

Three different models in the R2 series and four models in the C2 series are available that all differ by the kW they require and the maximum hot water flow rate they can produce.

Out of all the seven models, only two models (X models) require 208V, whereas, the others (E models) work on a 240V supply.


  • Extremely small units that can be installed easily.
  • These are capable of being installed in small spaces and are perfect for single application uses.
  • The heating elements are threaded and can be replaced easily.
  • These units have a soft starting feature.


  • For electric units, these units are not very efficient.
  • Expensive upgrades may be necessary from the user’s existing electrical configuration.
  • The temperature of the hot water may be reduced when used for multiple applications simultaneously.

Four Chamber Models

These are high-performance units that are capable of providing higher flow rates than the two-chamber units. These units are also available in two types for residential hot water heating and commercial applications.

The names of the two series are R4 and C4. These units are equipped with self-diagnostics features and a shut-down system for if the units start leaking.

These units are extremely energy efficient and can save a significant amount of money on electricity bills. The four-chamber models have a Uniform Energy Factor of 0.92.

Wattage requirements vary from 18 kW to 32 kW for both the series. Models that work with a 208V supply (X models) and a 240V supply (E models) are available each of the R4 and C4 series.

The maximum flow rate is supplied by the 32kW models that can produce 10.6 GPM for a 20˚F temperature rise.

These units are bulkier than the 2 chamber models because of the extra heating elements. All the units weigh 20 pounds. They are, however, capable of providing hot water to small or medium-sized whole homes.

Additionally, these units are easy to install and maintain owing to their light weights and scale detection features.


  • Capable of being used in small or medium-sized homes. The smaller models can be used for point-of-use applications as well.
  • These units have a warranty period of 5 years.
  • Compact, light-weight, and easy to install and maintain.
  • No venting is required for electrical units.
  • These units are equipped with dry fire protection and scale reduction technology.


  • The current electrical configuration may need costly changes to accommodate these units.


AO smith manufactures highly efficient and energy-conserving products that are capable of saving money on utility bills.

Apart from this, a wide range of products is also offered by the company from which the users can choose whichever product meets their daily hot water needs.

When sized and installed appropriately, these tankless units are capable of delivering maximum performance throughout their lifetime.

If you are looking for tankless units to replace your outdated tank-style heaters, AO Smith’s products are definitely worthy of your consideration.

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Our team consists of enthusiastic and passionate people from different fields and experience. Some are geeks and spend most of their time among gadgets while others love nature and are always on the move! We spend 10s of hours researching and writing on each topic. The articles are then quality checked by our editors. View our "About us" section for more details about process and team.

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