Takagi Tankless Water Heaters
Review and Buying Tips

A review of popular Takagi water heaters, including ultra-efficient and low NOx Takagi T-H3 models. Explore the most advanced Takagi tankless models with condensing technology, reaching high energy efficiency of over 95%. Check out the best models and features to look for, from small to large homes, using one or multiple fixtures.


Top selling models

Features to look for and benefits

Takagi water heaters are equipped with many advanced and advantageous features ensuring high performance, efficiency, better user experience, comfort, and significant savings. Some of the top features are:

  • Takagi water heaters provide flexible venting installation. This is possible due to its ability to use indoor, outdoor, and direct vent conversion kits, concentric and dual-pipe systems, and terminating horizontally or vertically.
  • The largest Takagi models provide sufficient hot water flow from one to several bathrooms. With the Multi-Unit and Easy-Link options, users have an opportunity to connect two or more water heaters into one system and get more power and a higher water flow rate, which is needed for high demanding applications.
  • Most of the tankless units are equipped with an electronic circuit board and microprocessor, which control the whole operation and provides enhanced safety and advanced monitoring, including diagnostics and error code notifications.
  • Inside the combustion chamber, dual-flame sensors ensure greater safety.
  • With the air-fuel ratio rod and computerized operation, water heaters ensure clean gas combustion, better performance, and efficiency.
  • A temperature controller is integrated into some models and provided with others, ensuring more convenience and higher savings.
  • The best models utilize commercial-grade materials for heavy-duty conditions and long-term use.
  • A primary heat exchanger is the standard element, and only in top models is made of commercial-grade copper alloy - HRS35, which gives more strength than the regular type (commonly used) copper.
  • A secondary heat exchanger is made of corrosion-resistant 316L stainless steel, and it is found on condensing models only (T-H3 and 540P models).
  • A bypass and flow adjustment valve built-in in some commercial models that deal with the high hot water demand.
  • Every model has several safety features to protect the unit from freezing, extremely high temperatures, and overheating.
  • The manufacturer provides a great warranty of 15 years on the heat exchanger and 5 years on other parts.

Takagi models review

Takagi T-H3 tankless water heaterTakagi T-H3

Takagi offers several models with tankless technology designed for residential and commercial applications, where the most advanced models include condensing technology, integrated digital controls, “green” combustion, and efficient operation.

For easier selection, we will group all the tankless models into three categories, so depending on your home size, you can select one either for small, medium, or large-size homes.

Sizing guidelines

To choose a suitable Takagi model, you have to know what size to look for.To properly size the heater, consider the following factors; peak flow requirements, temperature rise (the difference between outgoing and incoming water temperature), and types of applications.

Flow rates

To calculate the peak flow requirements or how much hot water you need at one time, use the chart below. See how many applications are to be used simultaneously and add those numbers to calculate the total sum of the water flow.

Application Average
flow (GPM)
temperature (F)
Tub 1 102
Shower 2.5 104
Washing machine 2 120
Dishwasher 1.5 110
Kitchen sink 1.5 110

Example: If running three applications simultaneously: 2 showers (2.5 GPM) and a washing machine (2 GPM) (2x2.5+2=7 GPM), the total flow rate is 7 GPM. To get enough hot water, choose a model from Takagi T-H3/540P series.

Below is the table with the available Takagi models, water flow, and a number of fixtures it can supply, and for two regions – warmer with the temperature of the incoming water of 70 F and colder – with the temperature of water 50 F.

Water flow 
# of showers in
warmer region
# of showers in
colder region
T-KJr2/110 4.6 2.5 1.5
T-K4/310 6.2 3.5 2.5
T-D2/510 6.5 3.5 2.5
T-H3M 4.5 2.5 1.5
T-H3J 6.1 3.5 2.5
T-H3S 6.8 4 2.5
T-H3/540P 7.6 4.5 3

Small size models – great for homes with one to two bathrooms

Takagi T-KJr2 series

Takagi T-KJr2-IN and T-KJr2-OS models are the smallest tankless water heaters that use only one heat exchanger, making them non-condensing. These are recommended for homes with one to two bathrooms, apartments, cottages, and condos, and indoor (T-KJr2-IN) and outdoor (T-KJr2-OS) installations.

Takagi T-KJr2 models are designed for an efficient and cost-effective way of residential water heating and can be combined with a radiant floor or baseboard heating. Takagi T-KJr2-IN can be converted into direct vent models for use in confined areas with the appropriate venting kit. The temperature controllers are provided for convenient use. The heaters use a two-pipe vent system for an efficient and low NOx gas emission to the outside atmosphere.

110C series

TK-110C-NI is a non-condensing unit designed for indoor use only, and it comes with the one-pipe concentric vent option. Small size, great for small houses and apartments. This is an ultra-low NOx model that has the temperature controller built in.

110U series

An indoor model TK-110U-I also comes with an integrated temperature controller provided for an outdoor model TK-110U-E. The model has a small size, so it is great for small houses and apartments. Ultra-low NOx gas emission. Non-condensing.

Similar model: Rinnai RL75

Medium size models – great for homes with up to three bathrooms

T-K4 series

Takagi T-K4-IN and T-K4-OS are non-condensing, tankless water heaters designed as indoor and outdoor models with the water flow capacity and energy efficiency sufficient for heating water in homes with up to 3 showers - working simultaneously. The remote control is not built-in but is provided as the standard feature. The venting system of the indoor model uses the two-pipe system. Low NOx emission.

310C series

TK-310C-NI is a non-condensing indoor unit that comes with a concentric venting system for easier installation. It meets the ultra-low gas emission requirements. It comes with a built-in temperature controller.

310U series

The 310U series offers two models; an indoor TK-310U-I that uses the two-pipe venting system and an outdoor TK-310U-E model, which is vent-less. An indoor model comes with the integrated temperature controller, while it is provided with the outdoor unit. These are ultra-low NOx models.

Large size models – great for homes with up to four bathrooms

D2 series

Takagi T-D2 water heaters are designed for residential and light commercial applications and indoor and outdoor installation. Up to 4 heaters can be connected to one system using the Easy-Link communication cable. They utilize the commercial-grade heat exchanger.

510 C series

Takagi TK-510C-NI comes with the concentric vent option making installation much easier. It is available only as an indoor model. Due to its powerful burner and commercial-grade heat exchanger, it is recommended for heavy hot water use. It meets ultra-low NOx requirements.

The model can be used in homes and commercial applications. It is designed for residential water heating, combination space heating, and recirculation systems. With the Easy-Link communication cable, up to 4 units can be connected, while the Multi-Unit controller allows up to 20 units. The temperature controller is built-in.

510U series

510U series comes with almost the same features as the above 510C series (including the Easy-Link and Multi-Unit systems), with the difference that the indoor model TK-510U-I uses the two-pipe system. There is also an outdoor type - TK-510U-E, designed for homeowners who prefer outdoor installation.

H3M, H3J, H3S and H3 series

Takagi water heaters from the H3M series have the lowest water flow rate, while the H3 models are the most powerful and have the highest hot water delivery rate.

All the models from Takagi H3 series are Ultra-low models and Energy Star compliant. Indoor models come with the two-pipe vent system and integrated temperature controller, while the outdoor models are ventless and come with a separate controller. Only the T-H3-DV-N and T-H3-OS-N use an Easy-Link or Multi-Unit controller to connect more units into one system and provide more hot water.

540P series

Takagi water heaters TK-540P-NIH and TK-540P-NEH are tankless and condensing water heaters that can provide instant hot water. How? The series integrates a recirculation pump and a dedicated recirculation line.

A temperature and pump controller are integrated into indoor models and provided with the outdoor units. These units are also ultra-low NOx compliant and can use Easy-Link for more hot water delivery.

Similar model: Rinnai RUC98


110C/110U 310C/310U 510C/510U 540
UEF 0.81 0.82 0.81 0.93-0.95
Condensing No No No Yes
Energy Star No No No Yes
Water flow
6.6 8 10 10
Recirculation No No No Yes
Easy-Link No No Yes Yes
Yes Yes Yes Yes
15 15 15 15

T-H3J T-H3 T-H3S T-H3M
UEF 0.94-0.95 0.93-0.95 0.94-0.95 0.9-0.91
Condensing Yes Yes Yes Yes
Energy Star Yes Yes Yes Yes
Water flow
6.6 10 8 6.6
Recirculation No No No No
Easy-Link No Yes No No
Yes Yes Yes Yes
15 15 15 15


While there are many tankless models to choose from, Takagi T-H3-DV is one you should consider buying. Takagi T-H3-DV is a tankless water heater with condensing technology designed for heavy usage in a residential home.

There are several notable features behind the modern look, such as cutting-edge electronics and a powerful gas burner. The model can reach a high 199,000 BTU, so the water is heated with the ultra-high energy efficiency of 0.95 and delivered to a maximum of five fixtures with up to 10 GPM rates.

Why should you choose a tankless water heater?

Tankless water heaters, such as Takagi, do not store hot water as the conventional tank type. Tankless models heat water on demand when it is passing through one or two heat exchangers. Those models with two heat exchangers are called condensing. And they are the biggest energy savers. This is important because up to 25% of the home’s annual energy use goes on water heating.

Another great advantage, except on-demand heating, is the unlimited supply of hot water. The advanced models are controlled by the built-in computer, allowing improved temperature control, accuracy, enhanced safety, convenience, and comfort. Also, reliable and durable operation is featured.

Takagi water heaters are compact and lightweight that comes with the size of a small suitcase, allowing easy handling and installation. The wall mount, long vents, and flexibility in the design ensure unit installation almost anywhere inside and outside the house.

If you require professional assistance, contact your local water heater expert! Get FREE estimates here

About Takagi

Takagi Industrial Co. is one of the four popular Japanese manufacturers of tankless water heaters sold in the US. The headquarters is in Japan, and Takagi has been designing and producing water heating appliances since 1952.

According to the manufacturer, Takagi water heaters are the first units with a continuous water supply and on-demand heating that entered the North American region.

Also, Takagi is among the first ones who offered a model, T-H1, with an ultra-high thermal efficiency of close to 95%.


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