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Tankless Water Heater For Radiant Floor Heat [Top 3 In 2023]

Tankless water heater for radiant floor heatbes

Looking for another alternative to generate hot water while keeping the electricity bills low? You should definitely consider investing in radiant floor heaters. Not only is it economical but also energy efficient.

Here we are going to list down our top three tankless water heater for radiant floor heat that can help you decide on which kind of tankless water heater to go for.

Comparison Chart

ProductTypesFeaturesOur Rating

Takagi T-H3-DV-N Tankless Water Heater
Natural Gas

Max BTU: 199,000 BTU/hr

Flow Rate: 10 GPM

Dimension: 11.2 x 17.8 x 24.9 inches

Weight: 59 lbs

Price: $$$

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Ecosmart 18 Tankless Water Heater

Flow Rate: 2.5 GPM

Dimension: 17 x 14 x 3.5 inches

Weight: 11.25 lbs

Price: $$

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Rinnai RU199iN
Natural Gas

Max BTU: 199,000 BTU/hr

Flow Rate: 11 GPM

Dimension: 22.05 x 14.76 x 33.86 inches

Weight: 84 lbs

Price: $$$$$

More Details

3 Best Models for radiant floor heating [Detailed Reviews]

1. Takagi T-H3-DV-N

Takagi T-H3-DV-N

This model is simply the best for radiant floor heating and the one that deserves 1st position. With this model, you can enjoy up to a maximum flow rate of 10 gallons per minute with a BTU rating of 199,000. It also has 2 heat exchangers that can instantly heat the water to the desired temperature with a 93% energy efficiency rating.

Overall, you will be getting a gas-powered unit that is outstanding when it comes to supplying a radiant floor heating system with sufficient hot water. It also has an ENERGY STAR certification and built based on the latest technology.

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2. Ecosmart 18 Electric Tankless Water Heater

Ecosmart 18 Electric Tankless Water Heater

This model we have here is completely different compared to the first model as it is a fully electric model. The manufacturer is known for its ultra-efficient water heaters and we even rate this as the #1 choice in our best electric tankless water heater post.

Its self modulating technology uses the lowest amount of energy at any given moment in heating up the water. This function makes it a solid choice for in-floor heating. With this feature, we are looking at 99.8% energy efficiency that is very impressive as it can save you lots of money.

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3. Rinnai RU199iN

Rinnai RU199iN radiant floor

Like the Takagi T-H3-DV-N, this model also uses natural gas but is actually more powerful (11 gallons per minute for water flow). Due to its higher power and performance, it will be able to heat the water circulating under your flooring, right on demand.

It also has a BTU rating of 199,000, maintaining a higher efficiency energy rating of 93 to 96% and comes with a 15 years warranty on the heat exchanger and 5 years on other parts. 

In terms of pricing, we think it is on the higher side. Although it is more powerful and efficient than the Takagi T-H3, it is almost double the price.

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Buyer's Guide

In our buyer's guide, we will list down all the features and factors that must be taken into consideration when looking for radiant floor tankless water heaters. After going through this article, we do hope that you will be able to determine which model is best suited for your expectation. 

Power Source

gas vs electric tankless water heater

Here we can see that there are two main types. You can choose between a tankless water heater which uses gas or propane and the ones that use electricity. The second type can be furthermore divided into two categories, point of use and the whole house.

Point of use will feed just one sink or shower with hot water. The whole house will obviously provide hot water for all sinks, showers, and faucets in that home. Electric units are extremely small and they can be installed under a sink, but they have lower hot water flow output.

Gas-powered units offer a much higher flow, but they are more complicated to install. They obviously use gas, but there are two versions. The ones that use gas, and those that run on propane. Find out more about these types of heaters in our best gas tankless water heater article.

For most of you, gas-powered models are a better choice. Keep in mind that all of them can be divided into older (models that have on and off switch) and newer which use modulating technology.

Self-Modulating Technology

The radiant floor heater must come with self-modulating technology. As the name suggests, you will be able to use a device which is clever or capable of adapting. In simpler words, this means that the hot water heater will use the lowest amount of gas or electricity to heat up the water. They use a valve which features different open or closed processes.

Gallons per Minute Flow

As you may recall, we have mentioned this factor several times in our reviews and this is an essential factor if you are thinking about using water heater to heat the house. It refers to the water flow per minute. For example, we have a model that offers 10 GPM. It obviously means that 10 gallons of hot water is available per minute. This amount will vary and it is unique for each model. You can browse models between 1 and 20 GPM.

Energy Efficiency

energy efficiency

Another factor which has to be taken into consideration. How efficient your new tankless water heater is? At the moment, gas-powered, models with a tank have 67% efficiency. A tankless is much better with 80%. Some are even rated at 99.9%, which is impressive.

All this means that you will save money on a monthly basis. On average, you are looking at 30-60% of money saving by installing a tankless water heater. This may be higher or lower and it will depend on the tankless water heater itself and the use of hot water. We must say that in this case scenario, more is better.


You were able to see that some models require specific ventilation. This refers to the gas-powered units only. It is an added expense when installing the unit, but it is a one-time investment and it isn’t as expensive as you may believe. Nevertheless, keep in mind that you will have to make some adjustments to the installation place.


Some units can be installed indoors and outdoors, while others must be installed indoors only. Make sure to use the manufacturer’s recommendations or you can damage the unit, which isn’t a smart thing to do and repair will cost you!

If it isn’t installed properly, you will lose a warranty, which is the second main issue here. Hence, it is advisable to seek professional for installation.


One of many reasons why a homeowner will choose a tankless water heater is the space saving. We all know that these models are the best when it comes to the amount of space they require. In order to get the best one, look for dimensions and the installation place at your home.

Frequently Asked Questions

1. Can I use a tankless water heater To Produce radiant heating?

Tankless water heater can be used to produce radiant heating. However, it is important to understand that not all of them are suitable for this task. Make sure you invest in a high efficiency tankless water heater. 

2. How do you heat a floor with hot water?

To heat a floor with hot water, hot water will flow through the pipes that are found directly below the floor or via electric mats, creating radiant heat that warms up the entire floor.

3. What temperature should radiant heating water be?

The temperature of radiant heating water should be in the range between 85°F to 125°F.

4. How long do Heated floors take to heat up?

Floors normally take around 30 - 60 minutes to heat up. However, it also depends on the type of insulation and floor covering you are using.

Final Verdict

Takagi T-H3-DV-N Heater

The best tankless water heater for radiant floor heat is the Takagi TH3 Natural Gas. This model has the most impressive flow rate, well-made and comes with the best warranties. As such, we rate it with 5 stars out of 5. It is the safest choice as well.

Other models on the list are more on purpose-based and they can be the best choice for some of you.

Our Rating

What we Liked:

  • Energy Efficient
  • Advanced Safety Features
  • Energy STAR certification
  • Superb flow rate
  • 15 years warranty on heat exchanger, 5 years on parts

What we Disliked:

  • Only for indoor use
top choice for radiant floor heat

    Verner Ellen

    Hi, my name is Verner Ellen. I am a homebody whose interest is in getting the best home tools and equipments to help with the the everyday house chores. I also love fitness, cooking and grilling. Maintaining a clean and comfortable home is my lifelong passion.