Takagi Tankless Water Heater T-K4-IN-NG

Takagi T-K4 Indoor Tankless Water Heater Natural Gas

(Takagi T-K4 Indoor / Natural Gas Heater)

Choosing the right water heater is not an easy or pleasant task for most homeowners. Just running a quick Google search on tank options can be quite overwhelming. You need some sort of advice or direction to choose the right path and to save your time.

We’ve discussed before that choosing a tankless heater will take your water heating to the next level. There is a bunch of reasons for that. Tankless doesn’t require a storage tank, which means it doesn’t store hot water. Instead, it heats the water while it passes through the unit. That saves you space and energy while ensuring optimal hot water temperature!

If you decide to go with the gas tankless water heater, you basically have two options: propane, which may be more convenient in some cases, and natural gas, which comes with several potential benefits.

Once you decide to go with a natural gas tankless water heater options versus the old-school gas water tank, your search becomes more narrow and you now can concentrate on choosing the brand or manufacturer.

Takagi has been delivering innovative residential and commercial hot water solutions for over 60 years. Their line of tankless water heaters is unmatched in quality and diversity, providing the perfect hot water solution for any situation. Takagi is one of the more reputable manufacturers of natural gas tankless water heaters catered to homes of different sizes and even commercial properties. Other notable brands are Rheem, Rinnai, Bosch, Noritz.

Overview for Takagi T-K4-IN-NG

The design, amount of hot water and cost savings are all intertwined in the fully modulating Takagi T-K4-IN-NG model. This gas-fired tankless water heater is intended for indoor installation uses the air inside for its power vent combustion.

The built-in freeze protection is located in many models of their tankless heaters. This feature works great in sub-freezing climates to keep the water temperature within the heat exchange system from falling below freezing.

The T-K4 is NSF certified water heater and features a commercial-grade copper heat exchanger designed to run efficiently and reliably. With an included control the T-K4-IN-N is the perfect answer to all your residential or commercial hot water problems.
Temperature Remote Controller included ( TK-RE02 )
Power Cord included
Manual reset high limit switch
Internal Freeze-Protection System

Maximum Input Capacity Learn More190000 BTU
Minimum Input Capacity11000 BTU
Flow Rate at 40F Temperature Rise Learn More7.9 GPM
Flow Rate at 50F Temperature Rise Learn More6.2 GPM
Flow Rate at 60F Temperature Rise Learn More5.3 GPM
Flow Rate at 70F Temperature Rise Learn More4.5 GPM
Uniform Energy Factor Learn More0.80
Minimum Flow Rate0.5 GPM
Flow Rate at 77F Temperature Rise4.2 GPM
Low NOx Emissions Learn MoreYes

Electrical Data:
Voltage120 Volts
Frequency60 Hz

Safety Features:
Air-Fuel Ratio ( AFR ) sensor
Exhaust and Water Temperature Safety Control
Overheat Cutoff Fuse
Indoor installation only ( Direct-vent convertible )
Fully modulating, gas-fired, tankless water heater
Our SKU number(s): Takagi T-K4-IN-NG
The manufacturer model number(s): Takagi T-K4-IN-NG


Takagi takes several safety precautions in their heaters and did not skip out on these precautions with this T-K4 Indoor Natural Gas model.
Another nice safety feature of this Takagi TK-4 model is the air-fuel ratio sensor or the AFR. This option ensures that the proper temperature is set by the user. The system can initiate the ignition of heat, and then it monitors the heating system to regulate the gas and the water flow. Other safety precautions done by this heater would be the self-diagnostics.

This technology allows it to shut off if something appears wrong within the system. This would cover if the unit was to get too hot. The user can also manually reset the high-temperature limit switch, located on the heater. At the same time, the air-fuel ratio sensor will monitor and prevent possible clogged vent. It will also detect if the gas emission is being minimized. Having a system that can automatically take these precautions makes the system very secure.


The T-K4 Indoor Natural Gas Tankless Water Heater is one of Takagi’s small-sized on-demand water heaters. Having used the T-K3 version, this edition does improve on the prior model. It was easy to replace the previous T-K3 water heater since the T-K4 uses the same “4” venting system.
Like similar tankless water heaters, this compact tank may be placed horizontally or vertically. Ultimately, it is saving so much space than conventional water heaters.

Mounting the tankless T-K4 heater accurately is important. Make sure it is near the correct gas line and water pipe connections. Outside of that, the placement of this model was non-disruptive and fairly easy to do. The T-K4 works well in small to medium-sized homes and can easily work in apartments of varying sizes.

Takagi includes a remote control option which only adds to the 38-pound compact design. One comparison to the T-K3 versus the T-K4 would be the missing control panel in this newer model. With the added benefit of using your remote to better control the exact temperature of your water, losing the control panel from the previous version is not that noticeable.

The GPM for the Takagi T-K4 is quite impressive. When putting the tankless water heater to the test, it proves to perform well. For example, if you have a larger size home with 2 or 3 bathrooms, this tankless water heater can supply hot water to the running shower while also using hot water for your laundry load and dishwasher.
This efficient model can hold a maximum of 8 gallons per minute. In addition to the GPM, the exhaust and water temperature is safely controlled.

To ensure you are receiving the maximum use of this tankless gas water heater, make sure you are selecting the gallon capacity based on how many people and how frequently it will be used daily. With a maximum of 8 gallons per minute, you have to consider how many devices you normally run simultaneously with hot water. A lot of the negative reviews related to the heat capacity may be directly due to not considering the correct usage amount prior to purchasing.

One would think this would increase your gas bill because it is using more energy. With the Takagi T-K4-IN-NG, you could potentially end up saving up to 45% on your monthly gas bill. This is possible because the gas is only burned when hot water is needed.

The cold water is heated with the gas burner as it passes through the heating system when in use.
By not having a tank to continuously have hot water on hold, the Takagi T-K4 supplies what is needed. This proves to be not only efficient but also environmentally friendly since it is using much less energy consumption.


Depending on your connections, you may have to install additional equipment to connect the Takagi T-K4. This type of tankless gas water heater requires stainless steel venting. This may be something you have to special order depending on your current unit. One other drawback to this unit is the delay for the hot water to come through the faucet.

Since the water will run through the on-demand system and the gas will heat the water through the piping, there may be some lag time while the tank heats itself. This may be a pet peeve for some but others may not notice a difference from their previous water tank heaters.

If deciding to move forward with the Takagi T-K4 Indoor Natural Gas on-demand water heater, if you are planning to do your own installation, this would void the warranty. A licensed professional must do the installation if you are planning to maintain the 15-year warranty on the heat exchangers for residential users and the 10-year warranty for commercial use.

There is only a 5-year warranty for residential users on other parts of the model. This may cancel itself out if you are pricing a licensed professional against replacing the entire unit or any of its pieces.


The lifespan of the Takagi T-K4 Indoor Natural Gas Tankless Water Heater is expected for 20 years. This depends on the water level and the maintenance of the equipment. Energy efficiency, high-level performance, and simple design are outstanding features of this model. If you’re looking to own a long-lasting tankless water heater, this product is one to consider.

On the other hand, there several models of newer Takagi Tankless Water Heaters that are on the market right now that we recommend you to consider.

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