Best for Radiant Floor Heat

Best Water Heaters for
Radiant Floor Warmth in 2019

Radiant floor heating can be an economical and convenient way of uniformly distributing heat through out your home. When it comes to deciding on the best water heater for radiant floor heat, a highly-efficient tankless water heater is going to be the ideal option, for a number of reasons.

For starters, as tankless water heaters can instantly heat up water, they don’t have to be constantly running to provide hot water right when it’s needed. Adding to this, because of heat exchangers and temperature sensors working alongside the tankless heater’s computer modulator,  water will never be heated too much or too little. Because a standard water heater can’t alter its flame intensity or instantly provide hot water, there’s no way for it to accomplish what a tankless water heater can do so effectively.

What’s more, the whole process of a well-designed radiant floor heating system can be managed with a home’s standard thermostat and can permanently cut energy costs. For more information regarding our top water heater picks, check out the comparison chart below as well as the reviews that follow.

Water Heater for Radiant Floor Heat Comparison Chart

NameMax FlowEnergy SourceGas InputRating
Takagi T-KJr2-IN-NG Indoor Tankless Water Heater
Top Pick (Smaller Spaces)
6.6 GPMNatural Gas140,000 BTU9.8/10CHECK PRICE
Takagi T-H3-DV-N Condensing Indoor Tankless Water Heater
Top Pick (Larger Spaces)
10 GPMNatural Gas199,000 BTU9.8/10CHECK PRICE


Takagi T-KJr2-IN-NG Indoor Tankless Water Heater – Top Pick

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The Rundown

When it comes to pairing a tankless water heater with your radiant floor heating system, no brand does it better than Takagi. While a good number of on-demand tankless heaters can handle radiant floor heating, Takagi engineers their tankless water heaters with the process specifically in mind. Adding to this, Takagi products are lightweight, quiet, and use the outside air for combustion, meaning they’re direct-vented. Go to any forum or article talking about radiant floor heating and you’re bound to find yourself reading about a Takagi tankless water heater.

As you’ve probably already noticed, this article lists two different Takagi units as the best water heater for radiant floor heat. This first unit we review, the T-KJr2-IN-NG, is the smallest unit Takagi offers and is a great radiant floor heating choice for apartment unit-sized spaces. If you’re looking for a unit to handle larger spaces, skip ahead to the T-H3-DV-N review below, which can handle medium to large-sized spaces.

The T-KJr2 has dimensions of 13.8 x 6.7 x 20.3 inches and weights 38 pounds. Although small, this unit can reach a hot water flow of 6.6 gallons per minute. Additionally, it’s fully modulating, which means water will always be the exact temperature requested due to a copper heat exchanger as well as temperature sensors that regulate water temperature. Because of the T-KJr2-IN-NG’s well-engineered design, it’s a very efficient tankless water heater, with an 82% efficiency rating, and won’t use up fuel unnecessarily. The T-KJr2 has a minimum gas intake of 19,500 BTU and a maximum gas intake of 140,000 BTU, with a water connection of 3/4″ and a voltage of 120.

As this tankless water heater is made for the indoors, we definitely don’t recommend mounting it outside. Also, due to it using natural gas, it needs to be vented with a category 3 stainless steel. When installing, make sure it’s not sharing a vent stack with another appliance, and ensure it’s being vented to a side vent horizontally. While venting is necessary, the South Coast Air Quality Management District has certified the T-KJr2 as low NOx, meaning it outputs less than 14ng/J.

Some of the safety features for this unit include freeze, overheat and surge protection, as well as troubleshooting diagnostic codes. Included with purchase of the T-KJr2-IN-NG is a power cord and remote control, however, your radiant floor heating system can be set up to be managed via your home’s standard thermostat. Takagi provides a 15-year limited heat exchanger warranty and a 5-year limited parts warranty for residential use.



Takagi T-H3-DV-N Condensing Indoor Tankless Water Heater – Top Pick

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The Rundown

While the T-KJr2 is an excellent unit, Takagi has outfitted the T-H3-DV-N with premium features and materials, meaning it can handle much larger radiant floor heating tasks for both residential and commercial use. In fact, this unit has been NSF certified for commercial applications. This unit has dimensions of 11.2 x 17.8 x 24.9 inches and is decently heavier than the T-KJr2, at 59 pounds. Adding to this, it has a hot water flow of 10 gallons per minute, and like the T-KJr2 is also fully modulating. Unlike the T-KJr2, however, the T-H3′ has two heat exchangers; the primary heat exchanger utilizes commercial-grade copper alloy which allows for better heat transfer, while the secondary heat exchanger utilizes 316L stainless steel for better corrosion resistance. The T-H3 boasts a 93% efficiency rating and is Energy Star qualified. It has a minimum gas intake of 19,500 BTU and a maximum gas intake of 199,000 BTU, with a water connection of 3/4″ and a voltage of 120.

Like the smaller Takagi unit, the T-H3-DV-N is also an indoor unit and should not be mounted outside. As the T-H3 uses natural gas, it should be vented with Schedule 40 PVC, CPVC, PP and Category III stainless steel, and should not share a vent stack with another appliance. While venting is necessary, this unit complies with ultra-low NOx regulations, and outputs less than 14ng/J.

Safety features of the T-H3 are like that of the T-KJr2, which include freeze, overheat and surge protection, as well as troubleshooting diagnostic codes. A power cord as well as integrated controls come standard with this unit. Takagi provides a 15-year limited heat exchanger warranty and 5-year limited parts warranty for residential use. Adding to this, because this unit is commercial certified, Takagi also provides a 5-year limited heat exchanger warranty and 5-year limited parts warranty for commercial use.




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How Does Radiant Floor Heating Work?

Radiant floor heating works by installing electric heating coils or water-heated tubing under your floors. Then, the heat from the coils warms your floors and radiates through the room as well. It’s preferred over other heating options since it’s quiet, efficient, and feels good on the feet.

What Type of Flooring is Best for Radiant Heat?

The best type of flooring for radiant heat are tile, natural stone, laminate, and ceramic floors. These floor types won’t be damaged by heat exposure and don’t prevent heat distribution.

Primarily, you should avoid carpet, hardwood, and vinyl flooring. Carpet keeps heat in, which would make your radiant heat floor less effective. Hardwood expands and contracts with changes in temperature, which could damage it after long periods. And finally, vinyl risks changing color due to heat exposure over time.

Do Heated Floors Use a Lot of Energy?

Heated floors use less energy than you’d expect. According to the U.S. Department of Energy, heated floors are more efficient than baseboard heating and usually more efficient than forced-air heating. Part of what makes heated floors so efficient is that they rely on convection, which takes advantage of heat’s natural desire to distribute.

Hydronic systems (liquid-based) are great for homes who are looking to avoid increasing their electricity bill or rely on off-the-grid power sources.

How Long Does It Take for Heated Floors to Warm Up?

This is tricky to answer since it’ll depend on the type of floor you have, starting temperature of the floor, floor coverings, and other aspects.

For an idea – a wooden floor with insultation can take around 30 to 60 minutes to heat up. A concrete floor without insulation can take as long as two to eight hours. However, it’s worth noting that concrete stays warmer for longer once it’s heated.

Based on the floor you have – you might choose to leave the floor heated but on a lower setting. Floors are easier to heat up if you’ve left the heating system on a low setting and turn it up when you’re ready.  In fact, it’s more energy efficient to do this than to warm up the floor from zero every time.



Closing Remarks

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A well-designed radiant floor heating system has a great deal of pros, with little to no cons (if done correctly). When it comes to finding the right equipment for your system, no water heater can do the job more efficiently and effectively than a tankless water heater. Adding to this, Takagi is by far and large the best brand of tankless water heater for your radiant floor heating needs. With two Takagi options in this post, one for small applications and one for large, we hope you’re one step closer to consistent, economic, and even heating.



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13 responses to “Best Water Heaters for
Radiant Floor Warmth in 2019”

  1. Very Informative!

  2. Bill

    Can the Takagi unit be used for the radiant floor heating as well as serve as the household hot water source at the same time? We’re talking about 300 square feet of radiant floor plus standard two baths, laundry and kitchen. We’re having trouble finding a unit that works for both. Thanks!

    1. chris baschab

      Without getting into the task of figuring out the btu’s needed, it is best, and sometimes
      necessary to keep the floor heating system separate, ie a closed loop system. This will
      eliminate code issues, health issues and other problems. Of course, that requires a
      separate system for the house water. Don’t try to beat the system – do it right the first time.

  3. April Lewis

    Has the Takagi T-KJr2-IN-NG been used with a 60/40 glycol radiant system? Have a small room 9′ x 9′ with a glycol mix radiant loop in it would like to locate small unit for heating.
    Thank You

  4. Tom

    Please let me know what you come up I’m in the same situation. I’m considering installing two.

  5. Cody

    I do not have gas at my home. Is there an electric tankless water heater you would recommend for radiant in floor heating?

  6. James

    Do these water heaters work with propane?

  7. Harry George

    Building a new house in the mountains outside of Golden Colo.

    1. Tyler Seeger

      That sounds amazing!

  8. Arthur D Gravley

    Does Colorado Code permit the use of a tankless water heater in a closed loop radiant heating application?

    1. Paul Bromen

      Not sure about the codes in Colorado Arthur. We would contact your favorite local plumber.

  9. Angela Gordon

    It is really a very informational article.I just require a small help that I am getting Unusual sounds from my Heat Pump Water Heater for a couple of days. I have purchased it for about a year. I am unable to troubleshoot the issue.

  10. James Harvey

    Takagi T-KJr2-IN-NG works well and we are happy. It has a wall-mounted controller that allows you to set the water temperature. The controller can also display water temperature, outlet water temperature and flow rate. I set the temperature to 110 for a good hot shower and just turn on the hot water, I don’t need to mix hot water with cold water.

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