The Best Water Heaters for Radiant Floor Heat & Other Applications

The best water heater for radiant floor heat is a more energy-efficient, safer, more comfortable, and healthier solution than the conventional boiler and forced-air HVAC systems. It does not demand too much space for installation, and it ensures consistent and uniform space heating for the modern family.

Deciding which water heater to buy for radiant floor heating applications requires an understanding of several factors. These parameters can help prospective buyers decide what they need to look for in the ideal product.

Our search for the top-rated water heater for space heating purposes allowed us to identify three crucial factors.

Other factors can impact a water heater’s floor and wall heating performance. We will point out these other parameters in the succeeding product reviews and the comprehensive buying guide that follows.

Top 10 Water Heater for Radiant Floor Heat Reviews

1. EcoSmart ECO 18 Electric Tankless Water Heater

Many families consider the EcoSmart ECO 18 the top-rated tankless water heater for radiant floor heat because of its high efficiency and heating capabilities. Not only does it ensure more efficient space heating, this device can also be installed in DIY style without voiding its warranty.

Inside this super-compact water heater is a heating component that delivers 18,000 watts of power, heating the water in seconds. It is the perfect solution for people who want a small-footprint device that looks like a medicine cabinet on the wall.

I am not only surprised with this water heater’s 18-kW rating. Its 0.998 Energy Factor rating is also astounding. Its energy efficiency translates to almost-negligible heat losses, ensuring families get the warmth they deserve in their 1,800-square foot room.

This water heater for radiant heating also has a self-modulating technology that guarantees additional savings of up to 60%. The technology ensures efficient water heating with minimal electric consumption.

One might assume this electric tankless water heater for radiant heat comes with a hefty price tag. It does not, costing only about half the price of the RTE 13. It also comes with a lifetime warranty, unlike the 10-year period other brands offer. One can say this water heater delivers exceptional value.

Sadly, some people might dislike the product’s ‘Made in China’ labeling. However, I can guarantee it is an American brand with a manufacturing facility in China (think Apple and other well-known US brands).

2. Stiebel Eltron Tempra 20 Plus Tankless Water Heater

I love German technology and craftsmanship, and the Stiebel Eltron Tempra 20 Plus is one of the reasons why. This tankless water heater for infloor heating has a terrific heating performance, at about the same price as US brands.

I appreciate this hydronic heater’s 19,200-watt heating capability, providing warmth to a large room full of people. Although it delivers 19.2-kilowatts of water-heating energy, it only requires 80 amperes of residential electricity to run. Like all Tempra Plus Series water heaters, this product features an intelligent self-modulating technology that guarantees energy savings.

I also like its 0.99 EUF rating, minimizing heat loss while ensuring optimum space heating. I commend German engineers for using solid copper instead of stainless steel because the material guarantees faster and more efficient heat transfer. Its advanced water flow system gives this water heater exceptional water-optimization capabilities, delivering a sufficient hot water supply.

This tankless water heater for radiant heat floor application also comes with cutting-edge technology for effortless control. I love its clear digital display and easy-to-use control knob, including the preset temperature buttons and a real-time water flow and energy savings monitor. Children can operate this device without a fuss.

3. Rheem RTEX-18 Electric Tankless Water Heater

The Rheem RTEX-18 is an efficient and effective tankless water heater for radiant floor heating and other applications. It comes from a reputable company, giving confidence to buyers about its quality craftsmanship, performance, and overall value.

I like this hydronic heater’s 18-kW copper heat exchanger that raises the water to the desired temperature within seconds. Warming a room is never a waiting game. Family members can enjoy a warm and cozy environment immediately once they flip the switch.

This electric water heater for radiant floor heat has a 0.99 energy efficiency rating, which I find commendable because most products on the market offer less. The level of heat loss is negligible, ensuring the household gets a comfortable living space to enjoy the company of friends, guests, and visitors.

An essential aspect of this electric water heater is its intelligent self-modulation, ensuring easy temperature control and exceptional energy savings. One can install this in high-pressure water systems with 150 PSI. There are also no issues with its flow rate because the water heater can deliver a maximum of 4.4 gallons of hot water per minute.

4. Stiebel Eltron Tempra 15 Plus Electric Water Heater

I consider the Stiebel Eltron Tempra 15 Plus the top-tier electric water heater for radiant floor heat and other applications. This hydronic heater has exceptional energy efficiency and superb heating capability.

I love this tankless water heater’s 14,400-watt power capacity, making it ideal for heating living spaces as large as 1,400 square feet. As long as this radiant heating system works underneath floors or inside the walls, a family of five will never have issues with cold surfaces again.

The electric tankless water heater also has one of the highest UEF ratings on the market – 0.99. People will never worry about its 14.4-kW capacity because the water heater has intelligent self-modulating technology. The automatic modulator monitors the water heater’s electrical requirements. It ensures the device uses the least amount of electricity for heating the water.

I also like its advanced flow control mechanism, ensuring the household receives all the hot water it needs anytime. One will never worry about heating the floor or walls when a family member is showering, washing the dishes, or doing the laundry. The in floor heating water heater guarantees a sufficient water flow of 3.1 gallons per minute (GPM).

Its size and design are also unbelievable. This electric tankless water heater looks like a sturdy briefcase, measuring only 19.5 inches tall, 21.5 inches wide, and 8.5 inches deep. Its steel casing can also withstand earthquakes.

5. Takagi T-H3-DV-N Condensing Tankless Water Heater

Families who prefer a gas-powered hot water heater for infloor heat should consider the Takagi T-H3-DV-N. This high-efficiency gas water heater with condensing-modulating technology is as efficient as electric water heaters in ensuring comfortable living spaces.

I love this gas hydronic heater’s 199,000 BTU rating, capable of heating large rooms from 5,000 to 7,900 square feet. That is why many space heating experts also recommend this product to small commercial establishments. I can only imagine how warm a room will be with this product heating the space.

Many gas-powered hot water radiant floor heating systems have an efficiency rating of less than 70%. This water heater comes with a surprisingly high EF rating of 0.93 or 93%. Its heat loss is sufficiently low, making it almost comparable to high-end electric water heaters.

At its core is a commercial-grade copper alloy heat exchanger. It is 25 times more effective in transferring heat than typical stainless steel components. Delivering up to 10 gallons of hot water per minute is a cinch with this water heater, so I always have adequate space heating.

One issue that scares people from gas water heaters is nitrogen oxide formation. Families will never worry about this phenomenon with this water heater because of its outstanding engineering. It produces NOx gases but at ultra-low levels.

6. EcoSmart ECO 8 Electric Tankless Water Heater

I love EcoSmart products, despite some of them having a ‘Made in China’ label. I do not think it matters anymore, considering many American companies have overseas manufacturing facilities.

Small families with modest-sized living spaces should consider the EcoSmart ECO 8 electric water heater for radiant heat. This model has a tankless design and a powerful, 8,000-watt element to raise the cold water temperature to a comfortable 140 degrees Fahrenheit. It is perfect for floor heating, making icy and numb feet a thing of the past.

Although made in China, this product comes with a UEF rating of 0.998 – higher than many brands. Contributing to its exceptional energy efficiency is an advanced self-modulating technology and a solid heat exchanger. One can enjoy up to 50% savings using this water heater to warm floors and walls.

I am blown away by this hydronic floor heater’s compact form, measuring 11.5 inches tall, 8 inches wide, and 3.7 inches deep. It makes me wonder how a tiny device can deliver outstanding floor heating performance.

I looked at this tankless water heater radiant heat diagram and found that its installation and maintenance are a breeze. Although the components are as tough as rock, one can effortlessly replace them should they show signs of damage or wear.

7. Rinnai RU199iN Condensing Tankless Water Heater

Families with large living spaces can trust the Rinnai RU199iN tankless water heater for radiant heating. It has one of the highest BTU ratings among residential gas-powered water heaters and an admirable water flow rate the competition can only dream of having.

With its 199,000-BTU rating, this water heater can warm living spaces as large as 4,000 to 8,000 square feet while also providing hot showers to three people. Never again will families complain of refrigerator-like rooms or ice-cold bath times. This water heating appliance can make life more comfortable for everyone.

Although this gas tankless heater only has an EF score of 0.96, it is still 26 points above the industry average. I must reiterate that gas water heaters typically have an energy efficiency of 0.50 to 0.70, making this appliance a cut above the rest.

I also commend its maximum water flow rate as people can shower simultaneously and heat their floors. Eleven gallons of hot water every minute is several gallons higher than what other brands offer.

I also like its Circ-Logic technology, ensuring an ultra-fast water heating process. This product raises the water temperature within two minutes, making it stand out among gas-powered tankless heaters.

I commend the company for integrating an optional WiFi module into this water heater. I can be in my living room watching my favorite TV show, and I can easily control the appliance’s different settings.

8. Takagi T-H3M-DV-N Condensing Direct Vent Tankless Water Heater

The Takagi T-H3M-DV-N is a remarkable condensing tankless water heater that runs on natural gas. It is one of the most powerful hydronic heaters on the market, capable of heating large living spaces for everyone’s comfort.

I am surprised by this tankless heater’s two heat exchangers featuring commercial-grade copper alloy and stainless steel. Its heating components deliver 120,000 BTUs of energy, heating the water as quickly as one can imagine. Its heating performance is perfect for large households, eliminating annoying cold spots.

This hot water heater for radiant floor heat has a 0.90 UEF score, 20 points better than the industry average for gas-powered water heaters. Families will love the heat it generates, making rooms more pleasant for everyone.

Although it comes with a direct vent and a condensing design, this hydronic heater incorporates revolutionary technology. Households will never grow weary or anxious about nitrogen oxide emissions because this gas hydronic heater ensures NOx fumes are lower than 20 ppm.

I also appreciate this radiant floor heating hydronic heater’s maximum flow rate of 6.6 GPM. Other products can only offer half the capacity.

9. Rheem RTE 13 Electric Tankless Water Heater

I can understand why many people have Rheem water heaters in their homes. After all, it is one of the most trusted brands worldwide. The company’s RTE 13 electric tankless for radiant heat is also one of the best in the market, with its high energy efficiency, self-modulating technology, and high-power heating capability.

This water heater for radiant floor heating packs 13,000 watts of power, capable of warming a living space as large as 1,300 square feet. Family reunions and other social gatherings will never be chilly because this water heater supplies the in-floor tubing network with up to 4.0 GPM of hot water.

Although it does not have the Tempra 15 Plus’s 0.99 Energy Factor rating, I still commend this product’s 0.95 EF score. The heat it generates goes straight to the water with minimal loss.

Moreover, hefty electric bills are never a concern because of its self-modulating technology. The system only draws enough electricity to produce the best results.

The RTE 13’s form factor blew me away. The water heater only measures 10 inches tall, 7.25 inches wide, and 3.63 inches deep. For a device this compact, I find its 13-kW capacity astonishing.

The compact design also lends itself to DIY installation. At least, people no longer have to worry about paying a few hundred dollars for a professional to set up this system in their homes.

10. Marey GA10LP Power Propane Gas Tankless Water Heater

Some families prefer using propane gas instead of electricity or natural gas for heating. In that case, the Marey GA10LP propane boiler for radiant floor heat is an excellent choice. This water heater has effortless installation and an impeccable water heating performance no modern propane-using household will want to miss.

This water heater delivers 79,228 BTUs to warm a 1,600 to 3,100-square-foot living space, perfect for most small to medium-sized families. Meeting relatives for a fantastic dinner is more enjoyable with this device heating the water tubing network under the floor or inside walls. It creates a warm and toasty environment for everyone.

Its ingenious design gives families up to 60% savings from their electric bills. There is no fretting about a kilowatt increase in energy consumption because this water heater uses a battery to ignite its pilot light. Using a water heater for radiant heat has never been this economical. It also delivers a maximum of 3.1 GPM, sufficient to circulate hot water throughout the in-floor tubing network.

This propane water heater’s design is terrific, as well. It is lightweight at only 21 pounds, ensuring homeowners will not have issues with its installation.

I also appreciate its price tag, which is about 80% lower than the leading gas water heater brand. It is an excellent choice for families with tight budgets.

What to Look for When Buying Water Heaters for Radiant Floor Heat

Choosing the most suitable water heater for radiant floor heat is easy if buyers know what they should look for. Radiant floor heaters come in different types, including boilers/water heaters and resistance wire systems. Here are several things one must consider when buying the right hot water heater for radiant floor heating.

Heating Performance

The radiant floor heating water heater has a high kilowatt rating (for electric systems) or BTU rating (for gas-powered units). A hydronic floor heating system has a different sizing formula than conventional domestic hot water applications.

Adequate space heating power requires about 10 watts of electricity or 25 to 50 British Thermal Units (BTUs) per square foot of floor space. Hence, an electric hydronic heating system can be as low as 4,000 watts to as high as 20,000 watts.

On the other hand, hydronic heating systems running on natural gas or propane can produce up to 200,000 BTUs.

As a rule, one should always buy the hydronic floor heating system with the highest possible wattage or BTU rating for the budget.

Energy Factor

A hot water heater’s heat power is not the only thing buyers must look for when choosing the hydronic radiant floor heating solution. They must also consider its efficiency or the product’s ability to generate as much heat as possible without incurring significant losses.

In general, hot water heaters with a higher UEF rating are better than a product with an industry-standard rating. The electric water heater for radiant heating can have a UEF score of up to 0.95, although the industry standard is between 0.70 and 0.90.

On the other hand, a natural gas hydronic radiant floor system can have an industry-standard UEF of 0.50 to 0.70. The electric and natural gas tankless water heaters we featured here have a UEF rating of at least 0.90.

Energy Source

The hydronic radiant floor heating system’s power source also matters. An appliance that requires electricity as its power source is ideal for households without an existing natural gas pipeline. It is also perfect for families with low electric bills. An electric boiler for radiant floor heat is also less expensive than a gas unit.

Meanwhile, a gas-powered heating system is ideal if the family’s power source is natural gas or propane. The principal advantage of natural gas is its affordability, with a lower unit price than electricity.

Water Heater Type

We only included tankless water heaters in this review and guide because they deliver hot water instantly. A tankless model has powerful heating elements that raise the water temperature as it moves across the tubes. It is the perfect solution for radiant floor heating.

A tank-type radiant floor heating system can also work. However, the system stores the hot water in a compartment before distribution through the in-floor tubing network. It is how radiant floor heating works. The time it needs to heat the water makes a tank-type heater less efficient than a tankless system.

Warranty

Although not an absolute must, looking at the warranty of a radiant floor heating system gives buyers an idea of its quality and performance. No company will want to stand by its product indefinitely unless it is 100% certain about its safety, performance, and quality.

In general, a radiant floor heater with a 10-year warranty is better than one with a five-year guarantee. If buyers can get a radiant floor heater with a lifetime assurance, they know they have the best deal in town.

Is Radiant Floor Heating More Efficient

Yes, radiant floor heating is more efficient than conventional forced-air systems by 10% to 30%. It would be best to understand that water retains heat better than air, allowing water heaters to heat the floor and living spaces longer.

Water loses only 10 degrees Fahrenheit as it moves through the PEX tubing network underneath the floor. Water heaters only need to recover this heat loss to maintain a comfortable living environment. Such an attribute also provides households with up to 30% savings in their energy bills.

What Type of Water Heater Do You Need for Radiant Heat

The water heater people need for radiant heating depends on several factors, such as space availability, heating requirements, and primary energy source.

A tankless boiler for radiant heat is perfect for households with limited space, while a tank unit is more suitable for large homes with plenty of floor space to spare. Electric units are more energy-efficient and safer than gas-powered devices, although they are costlier to operate.

Regardless of the water heater type people choose, it should provide adequate space heating through the PEX tubing network under the floor and inside walls. Hence, one must pick a water heater that delivers the right temperature for a more comfortable living space.

How Big of a Water Heater Do I Need for Radiant Heat

Sizing a hot water heater for radiant heat is not as complicated as some people want others to believe. Everything depends on what hydronic heater one uses for heating the floor and walls.

It would be best to start with an accurate room measurement. One must multiply the room’s width by its length in feet to get the floor area in square feet. For example, a room measuring 30 feet long and 20 feet wide has a floor area of 600 square feet.

Heating floors or walls requires ten watts of energy per square foot. Using the example, multiplying 10 watts by 600 square feet results in 6,000 watts or 6 kW. Hence, a 6kW electric hydronic floor heater is sufficient for this room.

If one chooses gas water heaters, one must multiply the room floor area by 25 to 35 BTUs. Hence, a 600-square-foot room will require a gas water heater with a 15,000 to 21,000-BTU rating.

Older homes with poor insulation might require 40 BTUs per square foot, needing a 24,000-BTU heater in our example. Families living in colder climates might need as many as 50 BTUs per square foot, bumping the 600-square-foot heating requirements to 30,000 BTUs.

How Hot Should Radiant Floor Heat Be

The ideal radiant floor temperature depends on the occupants’ comfort requirements, pre-existing medical conditions, developmental age, and other factors.

A boiler system pipes in scalding hot water through PEX tubing under the floor, with the temperature reaching at least 180 degrees Fahrenheit. Unfortunately, these radiant floor heating systems have condensate that can corrode pipes.

Some people might also not tolerate the high water temperature of boilers. For example, older people and young children have thinner skins than adults, making it uncomfortable for them to walk barefoot on boiler-heated floors.

On the other hand, a radiant heat water heater delivers a safer and more comfortable 130 to 140 degree Fahrenheit floor heating.

Conclusion

The best water heater for radiant floor heat makes a modern family’s life more comfortable by providing them with a warm and cozy living space minus a boiler’s complicated setup and expense. It is a safe solution for children and older persons and an efficient system for energy-conscious families.

Among the ten water heaters for radiant floor heat we reviewed, the Stiebel Eltron Tempra 15 Plus comes out on top. It is energy-efficient, provides consistent water temperature to heat the floor and walls, and features an intelligent self-modulating technology for effortless and more economical operation.

Edward Manning

My work as a freelance copywriter allows me to work with Stephen later join Usawaterquality as a content producer. Our team works together to produce high-quality contents that cater to the needs of large companies and households.