Takagi TK3 Water Heater Review

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Takagi TK3 tankless water heater is the most popular gas model for water heating from Takagi manufacturer, designed for natural and propane gas. This article reviews the available models, its main features and advantages.

Takagi T-K3 is gas-fired, on demand water heater with the power vent as the standard feature and optional direct venting and sealed combustion. The flexibility in the venting system allows Takagi T-K3 water heater to be installed indoor and outdoor (outdoor kit has to be used) for residential and commercial applications.

TK3 model is mainly designed for water heating, but it can also be combined with the home space heating, in recirculation systems and for radiant floor and hydronic heating systems.

Features and Specs

takagi tk3

Takagi TK3, as said before, is the most versatile tankless water heater that can be used in multiple configuration by using the Easy-Link system.

This system allows Takagi water heaters to manifold up to four units into one system and provide hot water for high demand applications.


With its power vent system, Takagi uses the vertical or horizontal configuration with the 4" category III stainless steel for venting the gases out. If planning to use TK3 model in the environment contaminated with the chemicals (hair salons), dust, dirt... use the TK-TV10 conversion kit (purchased separately) to convert the TK3 power vent into the direct vent model with the sealed combustion, so the fresh air can be taken from the outside.

Power and Efficiency

Takagi TK3 is the Energy Star model, and thanks to the modulating gas control valve, it provides the heat power from 11,000 to 199,000 Btu/hr for both natural and propane gas where the energy factor EF is 0.84/0.86.

Temperature control

TK3 is designed with the eight pre-set temperatures; from 104 to 185 F and if you want to have more accurate control over your hot water, than you have to buy a temperature remote control TM-RE30 that allows temperature change from 99 to 176 F. Temperatures from 140 to 185 are for heating applications only.

Water Flow

Minimum water flow to initiate the gas burner is 0.5 gpm which is very convenient for small jobs like shaving or hand dishwashing, while the maximum hot water flow through the unit is 7.0 gpm. All the water and gas connections are using the standard 3/4" NPT.

T-K3 has two different modes of pump control, one is normal and the other is re-circulation.

Advanced features

Other important features are the electronic ignition with the flame sensor, numeric LED error code for easier troubleshooting and the computer that controls the water heater operation.


To protect the heating system, unit and its users, Takagi water heater is equipped with several safety features including:

  • Freeze protection system, consisted of several ceramic heaters built into the unit.

  • Hi limit switch that is set at 194 F and is manually resettable.

  • Thermistors to monitor the incoming and outgoing water temperature.

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

  • Flame sensor to verify the ignition and that flames are extinguished when the unit is OFF.

  • Air/Fuel ratio rod.

  • Power supply connection.

Model reviews

Takagi T-K3-OS

Takagi T-K3-OS tankless water heaters are the outdoor models with the energy factor of 0.82, making them Energy Star qualified for both natural and propane gas. T-K3-OS with its built-in power vent system is easy to install and perfect for the outdoor mounting in warmer areas.

When comparing to the standard Takagi TK3 models, this outdoor unit is designed with the lower maximum power which is 190,000 Btu/hr, and without an option to use the Easy Link system for higher demand application. But, it is easier to install as it doesn't require the Category III venting or vent caps.

Takagi T-K3-SP

Takagi T-K3-SP is another Energy Star water heater from Takagi TK3 series, designed for small hot water jobs. It has the same features as Takagi T-K3-OS but with an additional benefit, which is for users who prefer indoor installation. This Takagi model is also not linkable, and it cannot be converted to direct vent model.

For low demand commercial and residential applications such as space heating and domestic recirculation systems, use Takagi's Energy Star model T-K3-Pro. One of the advantages of the T-K3-Pro over other residential water heaters is its high grade heat exchanger made of the durable and resistant HRS35 copper alloy. Takagi TK3 Pro can be linked using the Easy Link system for higher demand application.

T-K3 model is advertised as the "Revolutionary T-K3" that was launched in 2007, making the Takagi manufacturer the first tankless water heater company that offers a "direct vent convertible" tankless model.

(Pictures courtesy of Takagi)