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Takagi T-K4-IN-NG Review – (Indoor / Natural Gas)

Table of Contents


Takagi-T-K4-IN-NG-ReviewReplacing a water tank heater is something that isn’t necessarily first on any homeowners list of favorite things to do. A lot of thought goes into purchasing a water heater.  Just doing a quick internet search on tank options can be so overwhelming.  Without some sort of direction, what are you really getting into?

Once you start the search and decide to go with a natural gas tankless water heater options versus the more traditional gas water tank, then you can start to narrow down the brand.

Takagi is one name that does come up quickly in searches and seems to understand the world of natural gas tankless water heaters so much that they have released several versions catered to different sized homes and commercial properties.

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.
Takagi takes several safety precautions in their heaters and did not skip out on these precautions with this T-K4 model.

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.


Another cool feature on the Takagi TK-4 Indoor Natural Gas model that also serves as a great safety feature is the air-fuel ratio sensor or the AFR. This ensures 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 temperatures were to get too high. The high-temperature limit switch, located on the heater, can be manually reset. Also, the AFR monitors against possible clogged vent and will detect if the gas emission is being minimized. Having a system that can automatically take these precautions makes the purchase that much more worthwhile.


  • Design

    The T-K4 Indoor Natural Gas Tankless Water Heater is one of the 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.

  • Gallons Per Minute

    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.

  • Cost Savings

    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.

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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 tankless 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.

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Wrap Up

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 upkeep 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 on-demand water heater, this product is one to definitely consider.

by Water Heater Mag

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