Takagi T-D2 and T-D2U Review

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An overview of the Indoor and outdoor Takagi T-D2 and T-D2U tankless water heaters for homes with two to four bathrooms. Check out the features that make T-D2/U models versatile and green.

Model review

Takagi T-D2-IN

Takagi T-D2 models (or 510 series) are coming from the non-condensing group of tankless water heaters where the energy factor, for both natural gas and propane models, is 0.82, which is the same as other tankless units from this group.

Takagi T-D2 heaters are designed as conventional on-demand models while the T-D2U models as ultra-low NOx, all used in residential and light commercial applications. These models can work as a single unit with the maximum water flow of 10 GPM, which is enough hot water for two to four showers, while when using the Easy-Link system, up to 4 units can be manifold into one system when they generate the maximum flow of 40 GPM.

Ultra-low NOx, or T-D2U models can utilize the multi-controller to connect up to 20 units and generate up to 200 GPM of hot water, which makes the units recommended for larger homes, restaurants, schools and beauty salons. T-D2 models are NSF approved so can be used in commercial food industry.


Takagi T-D2-OS

Takagi T-D2-IN models are built as the indoor units that can use either 3” or 4” vents with the maximum lengths of 50 feet, and can be converted to direct vent models with the correct conversion kit. There are also Takagi T-D2-OS models that do no utilize any venting due to the outdoor installation.

Built tough

Takagi T-D2/U are built tough, especially the heat exchanger that is commercial grade and has the thicker wall than other standard type, and is made of the hardened copper to sustain higher stress and allow longer life.


Takagi T-D2/U are not made for heating potable water only. Due to its capability to provide very high water flow and power, it makes them suitable for use in space heating and recirculation systems. The pump control port allows efficient operation of the circulation pumps.

emergency plumber


Takagi T-D2/U is the advanced type of tankless water heaters and is equipped with the remote control, which is found as the standard feature on many Takagi models. When using the remote control you can set the temperature on the unit in a range from 99F to 185 with the 19 options, while with the dipswitch setup you have fewer options.

Features review

  • High quality, commercial grade heat exchanger made of HRS35 copper alloy.

  • Bypass and flow adjustment valve for optimal control and precision.
  • Variety of installation options: indoor as direct vent and ventles outdoor.

  • Modulating gas burner

  • Can be used for heavy residential usage of hot water such as space heating and recirculation systems.

  • Temperature remote controller is included

  • The AFR sensor (air-fuel mixture ratio) for proper gas combustion, increased efficiency and low emission.

  • Easy-Link system for connecting up to 4 units.
  • Multi-unit system on T-D2U models, up to 20 units.

  • Other safety features include the overheat cutoff fuse, hi-limit switch exhaust, water temperature safety control and freeze protection system. The safety features are computer monitored and controlled.


Water Flow
(GPM) @ 30 F rise
10 10 10 10
Energy Factor
0.82 0.82 0.82 0.82
Min. Water Flow
0.5 0.5 0.5 0.5
Activation rate
0.4 0.4 0.4 0.4
Temp. settings
99-185 99-185 99-185 99-185
Electric consumption
139 138 138 138
Max. vent length
50 N/A 50 N/A
39 39 39 39


Takagi T-D2/U comes with the long warranty; 15 years on heat exchanger if used in residential applications or 10 years in commercial, and 5 for other parts.


Takagi T-D2/U

(Pictures courtesy of Takagi)