Takagi Tankless T-K4 Review

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Takagi tankless T-K4 and T-K4U review. Energy efficient and powered by natural gas and propane gas. High water flow for high demanding homes. Flexible venting with the outdoor installation or using direct venting and installed indoor horizontally or vertically.

Takagi tankless T-K4 and T-K4U are compact, wall-mounted and whole-house water heaters that are designed to provide on-demand and endless supply of hot water in the large amount. T-K4/U heaters are used for heating potable water and space heating in residential and commercial applications very efficiently and reliably for many years (much longer than tank-type).

T-K4/U water heater review covers:

Features and Specs

Advanced design

Takagi tankless T-K4 and T-K4U water heaters are built with many advanced features for convenient, safe and reliable usage. This includes the sensors, thermistors and the microprocessor, which initiates the ignition, monitors the heating operation, controls the parameters, modulates the gas and water flow to ensure the accurate temperature and factory set performance and efficiency. The computer also protects the unit by shutting it down if something goes wrong; high temperature, improper combustion, clogged vent...

Power and Efficiency

Both indoor and outdoor Takagi T-K4 and T-K4U models come with the full modulation, which allows them to work in the power range from minimum 11,000 to the maximum 190,000 Btu/hr and provide the maximum energy factor of 0.83. Modulating gas valve and water flow allows you to use the heater either you need its maximum power and flow or if the small jobs such as face or hand washing are needed.

Temperature control

If the remote control TK-RE02 is installed you can set the temperature of the outgoing hot water from 99 F to 167 F (for T-K4U model maximum temperature is 140F), but if it is not, then you should use a dipswitch setting, which offers only four temperature settings, which are in the range from 113 F to 140 F.

Water Flow

The hot water flow rate is limited, and the maximum flow is 8 gallons per minute or 264 gallons per hour for the First Hour Rating. If taking into account that you need 2 gpm of hot water for shower, it is easy to see that T-K4 model can supply hot water to up to three fixtures in warmer regions and up to two in colder.

Self-diagnostic system

The water heaters are self-diagnostic, so if there is a problem on the unit, the blinking red LED will display on the computer board, or if the remote is installed, an error code will be shown on the screen. Such a smart diagnostic system increases the safety and convenience when troubleshooting.

emergency plumber


T-K4/U incorporates several safety features:

  • Internal freeze protection system utilizes the electric heaters. The freeze protection activates if the outside temperature drops below 36.5 F. As long as there is an electric supply, the protection will work successfully.

  • Hi limit switch turns the unit off if the temperature increases over the maximum allowed... it is manually resettable.

  • Pressure relief valve (not supplied).
  • Thermistors to monitor the incoming and outgoing water temperature.

  • Overheat cutoff fuse to protect the heat exchanger from the excessive heat.

  • Flame sensor to check the ignition and presence of the flame.

  • Water flow sensor.
  • Air/Fuel ratio rod.

  • Power supply connection.

Takagi model review

Takagi T-K4/U-OS

takagi tankless tk4 outdoor water heater

Takagi tankless water heaters T-K4/U-OS are designed for the outdoor installation. The outdoor mount is ideal for those users who want to prevent any possible gas leak or leak of the products of combustion inside the home.

T-K4/U-OS models do not use any vent pipes since they are equipped with the power blower that blow the exhaust gases through the flue terminal directly out.

Takagi tankless T-K4 outdoor models should not be installed in very cold areas but in warmer. The outdoor units, when compare to the indoor model is easier and cheaper to install. If you want to cover or hide the water heater and plumbing, install the recess box.

Takagi T-K4/U-IN

takagi tk4 indoor water heater

Takagi T-K4/U-IN are indoor models, built with the sealed combustion, power vent and with the two-pipe system for air intake and flue gas exhaust. It requires the Category III, 4" flue pipe for safe removal of the exhaust gases out.

The vent pipe is 3" and can be made of the cheaper ABS, PVC... Maximum length is 50 ft and can be run horizontally through the outdoor wall or vertically through the roof.

You can also install the direct vent kit, a concentric termination that eliminates two separate openings for the air intake and exhaust. Direct vent termination use 4"/3" pipes on one side and one pipe for one penetration through the wall on the other, with the protective screen.

Takagi tankless T-K4 models are with its Energy Star compliance, great for heating potable water in bigger houses while protecting the environment by emitting less greenhouse gases and saving on energy.


Takagi T-K4-IN/OS

(Pictures courtesy of Takagi)