Takagi T-K3 Tankless Water Heaters Review

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See why Takagi T-K3 tankless water heater is one of the most versatile units. Explore the T-K3 benefits and features and see if this water heater really a "revolutionary" model.

This review covers the T-K3 series, which includes; the first convertible Flash T-K3 water heater, indoor/outdoor model T-K3-SP, indoor T-K3-IN and T-K3-PRO, for the commercial applications.

Takagi T-K3 series is one of the most versatile series between Takagi tankless water heaters, which is used not only for water heating but are designed for the recirculation systems, hydronic floor, and baseboard heating, or combination of potable water and space heating.

Takagi T-K3 features

Installation flexibility

Model T-K3 is the convertible tankless water heater designed for the outdoor installation that can easily be transformed into the direct vent model, for the indoor use.

By installing the conversion kit Tk-TV10, the unit becomes the indoor model with the sealed combustion. The power-vented flue and sealed combustion allow installations not only in a garage but confined space where there is not enough fresh air. The unit will get the fresh air through the 3" PVC venting pipe and run the exhaust gases through the 4" vent pipe, up to 50 feet.

For the outside installation, it is recommended to install the unit into the recess box.

Easy-Link system

The Takagi T-K3 produces a maximum of 5.4 GPM, but with the Easy-Link system, four T-K3 units can be combined and provide even more hot water. The maximum amount of hot water from this system is 26 gallons per minute with the 50 F temperature rise. Such an installation does not require the installation of the controller unit.


The temperature of the outgoing hot water can be set directly on the heater's dip switch, where eight pre-set temperatures are available (from 104 to 185 F), or through the TM-RE30 temperature controller, from 99 F to 176 F.


Gas modulating valve and electronic circuit board allows these water heaters to work in the range from 11,000 to 199,000 BTU and provide just enough heat for the minimum water flow of 0.5 GPM, or sufficient power of the maximum water flow of 5.4 GPM. The only requirement is to get a minimum water flow so the unit can work safely.

Takagi T-K3-SP and T-K3-OS


Takagi T-K3 or Flash T-K3 water heater was the first unit on the market with the conversion. Soon after, the company releases three other models; T-K3-SP as an indoor/outdoor model and T-K3-OS designed specifically for the outdoor use. These models are mainly built for the residential water heating, while the T-K3-Pro was built as the commercial model, for commercial water heating.

Another difference between T-K3 and T-K3-SP or T-K3-OS is in the power they generate. T-K3 is more powerful, as it comes with the gas input of 199,000 BTU (vs. 190,000 BTU) while the energy factor of 0.86 (vs. 0.82) provides more savings.

The good thing is that all the units are Energy Star compliant, which makes them eligible for grants and rebates.


The temperature of the outgoing hot water is factory set to 122 F and by changing the dip switch settings on the computer board you can select one of the four temperature settings (113 F to 167 F). The temperature controller TM-RE02 is a better solution as it allows you to set any temperature between 99 F and 167 F.

If the water heater is working without this controller, and if any problem occurs, the red LED light will be blinking (one to five times). If the unit has the controller installed, the numerical error code will be shown on the display (03, 11, 55, 70...). In both cases, Takagi water heater, thanks to the built-in self-diagnostic system, informs the user of the problem and makes the troubleshooting easier.

Safety features

  • Built-in freeze protection sensor

  • Manual reset hi-limit switch

  • Flame sensor

  • Overheat fuse

  • Flue backdraft pressure switch

  • Thermistors for constant temperature monitoring

  • Air fuel ratio

Takagi T-K3 series consists of the powerful and energy-saving water heaters, that heat water on demand and as much as you need. The greatest advantages are the flexible installation and the linking option for high demanding applications.

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Pictures are courtesy of Takagi WH company
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