Takagi T-K4-IN-NG Review

Having to replace a tank water heater is definitely a drag for any customer to go through. There are too many things to consider when going shopping for a water heater. The mere act of doing a little research online turns to be an overwhelming task. Without having any guidance, do you really know what you are purchasing?

When the research is over and you decided to go for a natural gas tankless model instead of the standard gas tank water heater, now you have to choose a brand.

Takagi is one of the main results that come out in a Google search. This brand is so acquainted with natural gas tankless water heaters that it has launched a lot of models meant to meet the needs of different type of houses and commercial purposes.

The layout, water flow and cost-effectiveness are corelated features embedded in the fully adjustable T-K4-IN-NG unit. It is a gas-powered tankless device for indoors that harness the air from the house to increase the vent burning.

Takagi is a very serious brand when it comes to adding safety to each of its devices, and the T-K4 model is not the exception.

Takagi incorporates the freeze protection feature in many of their models. This is an excellent function for sub-zero climates. It prevents the water inside the heat exchanger from getting down to freezing temperatures.


An awesome safety feature on the T-K4 Indoor Natural Gas Tankless Water Heater is the air-fuel ratio modulator (AFR). It monitors that the temperature that the user set is the right one. Once the ignition has started, it regulates the gas and water intake to keep them balanced. Another safety feature that stands out in this unit is the self-diagnosis.

This system shuts off the unit when something seems to go wrong with it. This could happen in the case of an overheating. The heater has a Max Temp Limit switch that can be manually adjusted. On its part, the AFR checks that there’s no clogging happening in the venting and will act if it detects a reduction in the gas rate. This technology taking care of all safety issues instead of having you worried while using it, is another reason for you to make your mind up about this product.


The T-K4 Tankless Water Heater comes from the series of compact instantaneous water heaters by Takagi. After using the T-K3 model, I must say this version really outdid its predecessor. Replacing the old T-K3 for this new model was easy because they both use the same 4-venting design.

Like other tankless models, this little device can be installed horizontally or vertically. It actually occupies much less space than standard water heaters.

Installing the T-K4 in the right place is fundamental. Place it near the gas line and the water outlets. Besides that, the installation of this heater was pleasant and quite simple to accomplish. The T-K4 is ideal for small to middle size houses and can work well for different types of apartments.

Takagi offers a remote-control device that comes only with the 38-pound small version. A feature present in the T-K3 and lacking in the T-K4 is the control panel. Anyway, with the convenient addition of a remote control for adjusting the temperature accurately, the absence of a central control panel is no drama.

GPM Capacity

The GPM of the Takagi-T-K4-IN-NG is amazing. When we first tried out the tankless unit, it showed a great performance. That’s to say, if you have a large house with two or three bathrooms, this machine will provide hot water for one shower and still have enough hot water left for your washing machine and to do the dishes.

This powerful heater can deliver up to 8 gallons of hot water per minute. Apart from the GPM, water flow and heating are strictly monitored.

To ascertain that you are making the best use of the Takagi T-K4, be careful to choose the gallon per minute depending on how many users and how often they will use it daily. Having a max capacity of 8 GPM, you should think about how many hot water applications you usually run at the same time. Many negative feedbacks complaining about its heating power might be because of not measuring the right usage amount before buying the product.


You might be thinking this model will rise your gas bills for demanding a lot of power. This heater could eventually make you save up to 45% on your gas bills. The reason of this is that this water heater only ignites when there’s a hot water demand.

The burners heat the water as it runs through the inside of the device when the faucet is running.

The lack of a water tank to heat continuously makes the tankless water heater heat when needed. That’s not only cost-effective, but also eco-friendly cause it uses less energy more efficiently.


Depending on your water outlets, you could need to buy adapters separately to install the Takagi T-K4. This kind of tankless devices need a stainless-steel venting, which you might have to buy separately in the case your current heater lacks it. The main disadvantage on this model is the time the water takes to be delivered through the faucet.

Since the tankless system heats the water on the spot and while it runs through the coils, it could take some time to get the water hot. This can be a drag for some users, but most people won’t even realize there’s any difference from their former tank heater.

If you’re planning to do a do-it-yourself installation, consider that this will annulate the warranty. You must hire a licensed plumber for the job if you want to keep your 15-year warranty on the exchangers and for household applications or the 10-year warranty for commercial applications.

It has just a 5-year residential warranty on the other parts of the unit. This warranty will be annulated if you hire a professional to replace the device or any of its parts.


The average lifespan of the Takagi T-K4 is 20 years. This may vary according on the water pressure and maintenance of the unit. Efficient consumption, high-quality working, and a simple layout are some noticeable features of this water heater. If you are looking for a durable on-the-spot water heater, this model could be just the one for you.

T-K4 and T-K4U are two compact Takagi tankless water heaters that can be mounted on the wall and heat water for the entire house. They supply hot water when asked in an uninterrupted flow with steady temperature, without distortions. Takagi’s tankless models are applied for warming potable water and the environment for household and commercial usages in an effective and reliable way, for a longer period of time than tank water heaters.

They are ideal for houses with up to 3 bathrooms in warmer zones and up to 2 bathrooms in cooler regions.

Design and functionality

Takagi T-K4 models are engineered like standard low-low-NOx models: T-K4-IN-N and T-K4-OS-N, and ultra-low NOx models: T-K4-IN-N and T-K4U/OS-N, made for indoor installation, outdoor installation and direct vent.

Note: The model names mentioned refer to natural gas units. To search for propane versions, add a P to the tail of the model name. That means that the propane version of the T-K4 DV-N is T-K4-DV-P.

Technological design – Takagi T-K4 tankless water heater

The Takagi tankless water heaters include several sophisticated features for a comfortable, secure and reliable operation. Sensors like the Air Fuel ratio, thermistors and microprocessors. All these features ensure a correct ignition, monitor the settings, regulate the gas and water intake, for a precise heating and personal adjustments made by the user.

It comes with a protective shut-off system in case that something is out of order: overheating, wrong gas burning, clogging or lack of air intake, and the consumption efficiency of the system reduces gas emission.

Powerful and efficient

Both indoor (T-K4) and outdoor (T-K4U) versions are fully modulable. This provides a heating range from 11,000 to 190,000 BTU an hour, as well as a limit energy factor of 0,82, much less than condensing heaters like the T-H3. Regulable gas burning and water pressure allows the owner to reach the maximum water heating and flow capacity as well as to meet low power needs like teeth brushing.

Lots of hot water

The water flow rate is restricted, and has an upper limit of 8 gallons per minute or 264 gallons per hour for the first hour. Considering that a shower requires an amount of 2 gallons per minute, we can state that the T-K4 can provide enough water for three or four applications in warm zones. And about two or three in cold zones (as stated by the maker).

Easy temperature settings

If applied, the remote controller TK-RE02 allows you to adjust the temp of the running water from 99 to 167°F (140°F in the case of the T-K4U). But if not, you must use a switch control with only 4 temperature levels, from 113 to 140°F. Both indoor and outdoor versions come with remote-control options. But they’re lacking a control panel as seen on condensing models like the Takagi T-K3.

Self-diagnosis feature for easy problem solving

The T-K4 has self-diagnosis that detects when something goes wrong with the system and indicates it with a LED blinking light on the control panel. And in the case of the remote controller, an error message will appear on the screen. This advanced diagnosis method makes problem solving easier and safer.

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