Takagi T-K4-OS-NG Tankless Water Heater, Natural Gas, Outdoor

Takagi T-K4-OS-NG Tankless Water Heater

Note: This product was discontinued by the manufacturer. We recommend you checkout our updated reviews of the best tankless water heaters on the market today.

Traditional water heaters with attached storage tanks have begun to decline in popularity in recent years, and the decline has never been more noticeable than it is now. As the demand for more energy efficient and technologically advanced water heaters grows, Takagi has stepped in to fill the gap. For the last 70 years, Takagi has painstakingly crafted a reputation for superior customer service and high-quality products, which has kept clients returning to the company ““ generation after generation.

The newest addition to the Takagi family of tankless water heaters is the Takagi T-K4-OS-NG Tankless Water Heater. This model is powered by natural gas. Unlike other comparable models, it is designed for outdoor installation only. Because it is installed out of doors, the unit continuously utilizes the fresh air for gas combustion, and its design features a powerful, built-in vent to remove the byproducts of combustion out of the way. The T-K4-OS-NG not only frees up space inside your home for other purposes, but it also eliminates the dangers that could arise should a gas leak occur. As an added bonus, it will also save you money since you will not need to revamp the venting in your home to install it.

Read on to find out more about what this amazing product has to offer!

Key Features

  • The Takagi T-K4-OS-NG has a maximum flow of 8 gallons per minute (GPM).
  • No venting is required to install this unit, which minimizes the cost of installation.
  • Built in freeze protection protects the unit during the cold months of winter.
  • The design includes inlet/outlet thermistors to ensure that the temperature is continuously monitored.


  • Self-modulation allows the unit to work in the range of 11,000 to 190,000 BTUs per hour.
  • A remote control is included to make it easy to change the hot water’s temp as needed.
  • The flow rate of 8 GPM is enough to supply up to four showers at once.


  • The warranties offered by Takagi are not as good as other competitors.

Product Review

The Takagi T-K4-OS-NG Tankless Water Heater is designed to be a wall mounted and compact whole home water heater. It can be utilized for both commercial and residential applications.

What sets this Takagi tankless water heater apart from competitors is the fact that it is loaded with technological advancements. The microprocessor, inlet and outlet thermistors, and sensors are responsible for igniting the ignition, continually monitoring its heating operations, controlling the preset parameters, and self-modulating the water and gas flow.

The internal computer protects the whole water heater by shutting it off should a problem arise, like a clogged vent or improper combustion. If a problem occurs, a red blinking LED (located on the front panel) will show up. If you have installed the remote control, then an error code will appear on it. Having this error code makes it much simpler to troubleshoot and diagnose what the problem is.

One of the highlights of the Takagi T-K4-OS-NG is that it is self-modulating in all aspects. This enables the unit to work within a BTU range of 11,000 to 190,000. With an energy factor of 0.83, this model is Energy Star qualified and certified. Because it can self-modulate the water flow and the gas flow, you can use this unit at almost any flow rate and temperature. The maximum flow rate for this model is 8 gallons per minute, which, according to the manufacturer, is enough to provide water for up to 4 running showers at one time. The temperature of the hot water can be set anywhere from 99 to 167 degrees Fahrenheit. A dipswitch setting is offered, which provides four different temperature settings to choose from ““ ranging from 113 to 140 degrees F.

One thing that consumers have appreciated is the number of safety features the Takagi T-K4-OS-NG offers. For example, it boasts an internal freeze protection system to protect the unit during cold weather. This system will automatically turn itself on if the outdoor temperature dips below 36 degrees F. Another highlight is the unit’s overheat cutoff fuse, which protects and prevents the heat exchanger from employing excessive heat. Likewise, internal flame sensors routinely check and the presence of the gas flame and the ignition.



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Thank You For Reading

The Takagi T-K4-OS-NG has enjoyed solid professional and consumer written reviews. At the time of this writing, many online reviewers have rated this model five stars..

The primary complaint users have had against this model is the fact that the manufacturer warranties offered by Takagi are not as good as those of their competitors. Takagi only offers a 5-year warranty on the heat exchanger and a three-year warranty on all other components; however, with that said, many reviewers have been using their units 5+ years with no issues. Overall, this tankless water heater will make a solid investment in any home.