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The Best Water Heaters for Radiant Floor Heat for 2023

Writen by Ronald Brown

Fact checked by Natalie Bridges

Only the best water heater for radiant floor heat can provide your family with the energy savings you need to live in a comfortable home. Tankless water heaters are more energy-efficient and eco-friendly than conventional boiler systems for heating floors, walls, and ceilings.

best water heater for radiant floor heat

Radiant floor water heaters can be challenging to buy for first-time users. We identified three crucial factors to help you choose the best for your home.

  • UEF Value: Energy experts laud radiant floor heating systems for their energy efficiency. However, radiant floor water heaters vary in their Uniform Energy Factor values. UEF ratings closer to 1.0 are the most energy-efficient. Hence, buyers should pick a water heater for radiant floor heating with at least 90% (0.90) UEF.
  • Heating Performance: Radiant floor water heaters come in two energy sources: electricity and natural gas or propane. A gas system’s BTU rating reflects its heating performance, while its electric equivalent is watts. As a rule, the higher the heater’s wattage rating or BTU, the better the heating performance. For example, a 100,000-BTU/hour or 20-kilowatt water heater warms the floor better than a 60,000-BTU or 15-kilowatt unit.
  • Flow Rate: Hydronic floor heaters also vary in their flow rates. Some products only deliver 1.5 to 2.0 gallons per minute, while more robust systems push more than four gallons a minute. Pick a radiant floor heating system with a sufficient flow to move hot water through the water pipe network under your floor.

If you choose wisely, you can also end up with a product with a dual-purpose design. It can deliver hot water to your appliances like any other water heater. So, how do you pick the best water heater for heating your living space?

Top-Rated Products

Best Overall

EcoSmart Water Heater


Best Looking

Stiebel Eltron Water Heater


Most Durable

Rheem RTEX-18


Table of Contents

Top-Rated Water Heater for Radiant Floor Heat Reviews

1. EcoSmart ECO 18 Electric Tankless Water Heater

If you want a reliable and high-performance tankless water heater for domestic hot water and radiant heat, I recommend checking out the EcoSmart ECO 18. Given that space and water heating account for 62% of US homes’ energy consumption, this product is always a good system to have.

At the core of this appliance’s phenomenal heating performance is its 18000-watt element, giving modern homes endless hot water supply for their floors, bathrooms, and kitchens. While 18-kW can translate to higher energy bills, you can rest easy knowing that it can slash up to 50% off your energy expenditures.

Its high-power rating makes it the clear choice for heating floors, walls, and ceilings. It can provide your family with the warm comfort you need, eliminating the use of any other space heating system. It is a space-saver, too.

I love the product’s Self-modulating Technology because it allows for more efficient space heating. It automatically adjusts the energy consumption to account for other variables.

This system can provide your home with up to 4.3 gallons per minute, depending on the inlet temperature where you live. You do not have to worry if the temperature’s not high because this water heater can still provide you with a respectable 1.8 GPM flow rate.

Some people might be upset about this product’s ‘Made in China’ information. Before you shrug it off your list, I would like to say that EcoSmart is Rheem’s subsidiary. You can still rely on its quality and performance because Rheem cannot afford to tarnish its reputation. It is a bit pricey, though.

It may have a Chinese tag, but the EcoSmart ECO 18 is the best solution you can have to address your space and domestic water heating needs. It is an excellent investment to provide optimum comfort for your family.
What We Like
  • 18000-watt power rating for more efficient water heating
  • Up to 50% energy cost reduction for better savings
  • Advanced self-modulating technology for hassle-free operation
  • High water output of 1.8 to 4.3 gallons per minute
  • A space-saving design
What We Don’t Like
  • Made in China
  • A bit pricey

2. Stiebel Eltron Tempra 20 Plus Tankless Water Heater

The Stiebel Eltron Tempra 20 Plus electric water heater radiant floor heat unit is a remarkable device that can provide non-stop space heating to any modern home. It has a powerful heating element that will never worry you about high energy bills.

While this unit operates at 19.2 kilowatts in a 240-volt system, it still maintains a 0.99 energy factor that is higher than conventional tankless water heaters. This unit ensures you will have the best cost savings while heating your home’s floor. Everyone in your house will feel warm and cozy.

I love its intelligent self-modulating technology because it ensures continuous energy savings. It automatically switches to the lowest temperature setting that provides optimum heating. The unit’s advanced digital display makes it a breeze to manipulate the unit’s different settings.

I also like the unit’s temperature memory settings. You can program a button to heat your floor at a balmy 86 degrees Fahrenheit or a toasty 140 degrees. The next time you run your unit at your preferred temperature, all you need is to press a button. It is that straightforward.

Unfortunately, its price tag makes it unappealing for those who want more water to heat their floors without spending a lot.

Nevertheless, the Stiebel Eltron Tempra 20 Plus remains the right choice for modern families who want an energy-efficient floor heating system. It is compact and provides your family with an uninterrupted hot water supply for your appliances and your space heating.
What We Like
  • 99 energy factor for greater energy savings
  • Intelligent self-modulating technology for better continuous energy savings
  • Advanced digital display for easy use
  • Temperature memory settings for effortless operation
What We Don’t Like
  • The cost is unappealing

3. Rheem RTEX-18 Electric Tankless Water Heater

If you think the Rheem RTE 13 cannot provide your house with sufficient space heating, I suggest considering the RTEX 18. This device is a powerful and compact wall-mounted appliance, perfect for hot water heater radiant floor heating.

With its 18-kilowatt rating, you can heat several rooms simultaneously without worrying about a substantial jump in your electric bill. Its self-modulating technology ensures you only use the right amount of electricity to heat your water or space to the preferred temperature.

What differentiates this unit from the RTE 13, you ask? Aside from a higher power rating, this product also comes with user-friendlier controls, complete with a cleaner and more aesthetically-pleasing look. I love its large and bright LED screen with its simple digital readout. You will never have issues determining the device’s output temperature.

The thermostat knob also looks clean and straightforward, allowing you to dial in your preferred temperature easily. You can set this unit’s temperature in 1-degree Fahrenheit increments, ensuring more precise temperature control.

Compared to the 20-kW Stiebel Eltron Tempra 20 Plus, this unit offers a higher maximum water flow of about 4.4 gallons per minute. It ensures more hot water for your activities while also keeping up with your space-heating needs.

The installation can be tricky, especially if you do not have a working knowledge of electrical systems. Some users also complained about fluctuating water temperatures. I think it has something to do with the unit’s self-modulating system that tries to balance power and hot water demands.

Regardless, I love the Rheem RTEX 18 because of its clean and elegant looks. It can also provide your home with a more energy-efficient system for delivering hot water to your appliances and fixtures and heating to your floor.

What We Like
  • 18-kilowatt unit for heating wide spaces
  • High maximum flow rate for sufficient hot water consumption and space heating
  • Advanced self-modulating technology for better energy savings
  • Straightforward thermostat control and clean, bright LED display
  • Compact wall-mounted design
What We Don’t Like
  • Tricky installation, especially for novices
  • Fluctuating water temperature

4. Stiebel Eltron Tempra 29 Plus Electric Water Heater

You might want to forget about buying a boiler for radiant floor heat because the Stiebel Eltron Tempra 29 Plus offers you a more significant deal. This hydronic floor heating device has a powerful heating element that warms your floor when you step through the door.

This tankless system uses a powerful 28.8-kilowatt element to get the water temperature to a maximum of 140 degrees Fahrenheit. The system can deliver a minimum of 3.1 gallons per minute and maxes out at 6 GPM. You can heat your floor in no time, providing comfort for everyone who ever sets foot into your home.

I like this product’s Advanced Flow Control system because it guarantees optimal water temperatures, regardless of environmental conditions. Temperature fluctuations are never an issue. You will also be glad that this model has a self-modulating system, ensuring the lowest possible energy that delivers optimum results. It is the appliance’s way of ensuring you get up to 20% water heating savings.

This tankless water heater for radiant heat floors also comes with a remarkable seven-year warranty against leakage and three years for its parts. Honestly, you will sleep better knowing the company has your back. The warranty also reflects product quality and performance.

This product is to tankless hydronic water heating system that BMW is for cars. It is pretty expensive.

Nevertheless, the Stiebel Eltron Tempra 29 Plus is a formidable water heater for bringing warmth to a large space. It is a powerful unit that can work to heat your floor and deliver hot water to your bathroom, washroom, and kitchen simultaneously without any substantial water temperature drop.
What We Like
  • High power design for faster and more efficient water heating
  • High water flow rate for optimum floor heating
  • Advanced Flow Control system for more consistent water temperature
  • Self-modulating Technology for better energy savings
  • 7-year leakage and 3-year parts warranty for peace of mind
What We Don’t Like
  • Has an expensive price

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

If you are a beauty salon or a small restaurant owner, you will want to get the Takagi T-H3-DV-N. This product is a condensing tankless water heater that can go head-to-head with the Polaris water heater.

While the product is ideal for small commercial space heating, ordinary homes can also take advantage of its performance. You can rely on its 199,000 BTU power to deliver sufficient hot water to four baths simultaneously without experiencing water temperature drops. You have to laud its commercial-grade copper alloy heat exchanger for its remarkable heating performance.

Controlling this hot water heater for a radiant heat floor is also a breeze. It automates the water and space heating process while also giving you a chance to monitor any problems. Its diagnostic features work hand in hand with its reliable safety technologies to provide you with a system that will serve you for many years.

Whereas most systems can only deliver about five gallons of hot water per minute, this baby offers ten. You will never have customers complaining about a cold business space. They will feel warm and cozy whenever they enter your establishment.

I can only imagine how your home will feel if you install this unit. Everyone will feel comfortable and never worry about high energy bills because natural gas heaters have a lower operating cost than electric-powered units.

The only real concern here is its price tag. You also have to add the professional installation cost, which can set you back further. I do not recommend installing this unit yourself because it requires a few critical elements.

While the Takagi T-H3-DV-N is expensive, it offers the best value because of its energy efficiency and lower running costs. It is perfect for space heating.

What We Like
  • Recommended for residential and small commercial space heating
  • 199,000 BTU for faster and more efficient heating
  • Reliable integrated controls, diagnostics, and safety features
  • Heavy-duty copper heat exchanger for optimum heat transfer
  • High flow rate for optimum water consumption
  • Lower operating costs compared to electric models
What We Don’t Like
  • Professional installation recommended
  • Expensive price point

6. EcoSmart ECO 8 Electric Tankless Water Heater

The EcoSmart ECO 8 is the perfect radiant heat water heater for small homes and individual rooms. It has a lower power rating than other units featured in this list. While it may have a lower wattage rating, the product still strikes me as a reliable system for heating a small floor space or delivering hot showers to a small household.

Because of its 8-kilowatt rating, you will never have to worry about spending too much on your electric consumption. It is efficient enough to provide your family with up to 50% savings on your water heating. You can earmark these savings for more worthwhile family adventures.

At its core is a self-modulating system, an essential feature of leading hydronic floor-heating water heaters. The technology automatically adjusts the device’s power draw to optimize energy use in relation to heating requirements.

Installing this unit is also a breeze. Although there’s no tankless water heater radiant heat diagram, a manual is available to make this a DIY activity. That is additional savings on your part, slashing dollars from professional installation fees.

Its heating element’s threaded design also helps with maintenance, allowing you to replace the component without breaking a sweat.

It is essential to understand that this unit can only provide your home with a maximum flow rate of 1.9 gallons, depending on cold water inlet temperature. As a Rheem subsidiary, the company also has its manufacturing facility in China. Some people may be averse to such an idea.

The EcoSmart ECO 8 is an intelligent system that heats your living space efficiently and cost-effectively. You can also use this product to bring hot water to your shower, kitchen faucet, and other water fixtures. It will not cost you a fortune, both in its purchase price and installation cost.

What We Like
  • For small spaces and households
  • Good balance between power and energy efficiency
  • 50% water heating cost reduction for optimum savings
  • Advanced threaded heating element for hassle-free replacement
  • Easy to install
What We Don’t Like
  • Manufactured in China
  • Lower maximum flow rate than other brands

7. Rinnai RU199iN Natural Gas Tankless Water Heater

The Rinnai RU199iN is a dependable and energy-efficient water heater for indoor heat. It has innovative technology that guarantees convenient operation and versatility no other system can provide.

At its core is a Circ-Logic technology that allows you to decide how to optimize the device’s heating performance. You can route your hot water under your floor to give yourself more efficient space heating. Flip a switch, and the system delivers 140-degree water to your kitchen faucet, shower, dishwasher, and washing machine.

There are no worries about the energy efficiency of this hot water heater for radiant floor heat. It provides a minimum of 0.93 uniform energy factor and maximum energy efficiency of 0.96. It is a lot better than other systems on the market without ever undermining its heating performance.

Its 11-gallon per minute flow rate is also a lot greater than what other products can churn out. You will never have issues of insufficient water supply or your floor not heating fast enough. It makes space heating so much more efficient.

I strongly recommend getting the optional WiFi module to make your space heating experience more magical. Very few systems can be as innovative as this product.

Some users complained about the product producing more condensate than other systems, producing a 2-gallon per week on average. It is also worth noting that professional installation is an absolute must, lest you are willing to forgo its warranty.

The Rinnai RU199iN is one of the most exciting water heaters I have ever seen. Its revolutionary features are enough to blow the competition out of the water. Factor in its high flow rate and energy efficiency, and you will see how phenomenal this water is.

What We Like
  • Higher maximum flow rate than similar systems
  • High energy efficiency factor for better savings
  • Advanced Circ-Logic technology for more efficient heating
  • Optional WiFi module for more effortless operation
What We Don’t Like
  • Professional installation required
  • Too much condensate

Outdated Products

Happybuy 12L Propane Tankless Water Heater (Outdated)

If you want a reliable and efficient appliance for your hydronic radiant floor heating, I suggest the Happybuy 12L Propane Tankless Water Heater. This product has a powerful heat exchanger that can provide warm comfort to your house without causing your energy bill to spike.

Unlike electric water heating appliances, this unit relies on propane gas. It allows you to save more money as you provide a more comfortable living environment for your family. It’s 80% thermal efficiency translates to less propane gas consumption to deliver the correct space heating temperature for your home.

I love this device’s intelligent design because it has dedicated buttons for almost everything. You can turn a knob to choose between summer and winter modes to optimize heating relative to ambient environmental temperatures. It also has gas and water regulator knobs, allowing you to fine-tune your gas and water consumption.

This hydronic floor heating system also has several protections to make its operation safer for everyone in your household. It protects against overheating, overpressure, freezing, and more. Such protections will make you sleep sounder, knowing the unit will not give you any headache when you wake up. I also love its colorful digital display that comes with digital icons.

While I like its energy efficiency, I wish this product could offer more than 11% energy savings. It is also disappointing that its maximum water flow rate is only 3.2 gallons per minute.

The Happybuy remains an excellent choice for budget-conscious households. It is more affordable than other systems and has hassle-free settings, too.

What We Like
  • Powerful heat exchanger to provide comfortable warmth
  • High thermal efficiency rating for gas savings
  • Sufficient protection against overpressure, overheating, freezing, and more
  • Dedicated knobs for hassle-free operation
  • Bright and colorful LED screen for ease of use
  • Suitable for budget-conscious buyers
What We Don’t Like
  • Lower maximum water flow rate than other brands
  • Modest energy savings

Rheem RTE 13 Electric Tankless Water Heater (Outdated)

Everyone loves Rheem products, including its RTE 13 Electric Tankless Water Heater. While this unit is perfect for point-of-use water heating, it has sufficient power to heat a small floor space. It can make your living room or bedroom more comfortable without incurring high energy expenses.

This product has a maximum flow rate of 4 gallons per minute, which is a reasonably high number. Plus, this product only requires 13 kilowatts to deliver a maximum of 4 gallons per minute. That makes it more powerful and more efficient than the ECO 18. Its Energy Star certification should erase any doubts you may have.

Like many hydronics floor heaters, this product has a self-modulating system that utilizes the least amount of energy to deliver maximum results. I also love its straightforward controls. There are no fancy switches to tinker, only LED lights and a simple knob to twist.

Inside this tankless water heater for radiant heating is a heavy-duty copper-brass heat exchanger. That is another reason to smile because you know this product will last you many years heating your floor.

While this product is compact and lightweight, I still recommend a professional installation. Its wattage and amperage ratings require using the correct wire gauge to prevent electrical safety issues.

As expected of any Rheem product, this water heater has a hefty price tag. It costs about twice the ECO 18, even though both products are under the same umbrella.

Overall, the Rheem RTE 13 remains an excellent choice for households that want to heat one of their room’s floor effortlessly and effectively.

What We Like
  • High maximum flow rate for optimum water consumption
  • Self-modulating design for improved operating efficiency
  • Straightforward user controls for worry-free operation
  • Energy Star certification for greater confidence in the product’s energy efficiency
  • Heavy-duty brass/copper heat exchanger for durability
What We Don’t Like
  • Should be installed by professionals
  • A bit more expensive than other hydronic floor heaters

What Is The Best Water Heater For Radiant Floor Heat/ Who Is This For


The best hydronic appliance for radiant floor heat is a tankless water heater. It does not require plenty of space for installation, unlike a conventional boiler or storage-tank water heater. It also operates at a lower temperature than a boiler, eliminating the risk of creating toxic condensation without undermining its heating capabilities.

A water heater is perfect for anyone who wants to heat their living space without exacting a heavy toll on energy expenditure. It is important to recognize that space heating accounts for more than 40 percent of an American household’s energy expenditure.

Water Heater For Radiant Floor Heat Buying Guide

Since energy efficiency is one of the greatest strengths of a radiant floor heating water heater vs. boiler, you should know how to choose the right product for your home. The following are several pointers.

  • Consider the Power Source

You have two choices: electric and gas. If you already have a natural gas supply in your home, it would be ideal to opt for a gas-powered water heater. If not, an electric version is always perfect. You have to remember that your choice of a water heater based on its power source will impact its cost and ease of installation.

  • Check the Energy Efficiency Rating

Everyone wants an energy-efficient appliance that can provide the most significant cost savings possible. If you consider yourself one of these people, you should get a product with a minimum energy efficiency rating of 0.90. The higher the rating, the more savings you can get from your unit.

  • Determine the Heating Performance

It is essential to recognize that water heaters have different heating performances. Electric water heaters have wattage ratings as an indication of their heating power. On the other hand, gas units come in BTUs per hour. Ideally, the higher the wattage or BTU/hour rating, the more powerful the water heater. You can heat your floor a lot faster and more consistently, too.

  • Check the Maximum Flow Rate

If you live in colder climates, a hydronic floor heating water heater with a higher flow rate will be advantageous. Choose a product with at least 4 GPM to ensure you have sufficient hot water circulating throughout your under-the-floor pipe network.

  • Assess the Overall Costs

There are two cost considerations whenever choosing a water heater for your space-heating needs: upfront costs and operating costs. In general, electric water heaters are less expensive upfront than gas units. However, their operating costs are higher than gas water heaters because electricity is more costly per unit than a unit of natural or propane gas.

Installation costs are also an additional consideration. Hydronic floor heating systems always require professional installation. Many professionals charge a certain amount for every square foot. Installing an electric water heater is also more straightforward than installing a gas system because of the complex ductwork.

Frequently Asked Questions (FAQs)


Can I use a water heater for radiant floor heat?

Yes, you can use a water heater to heat your floor. In the past, most households used a boiler system for space heating. Unfortunately, boiler prices have gone up, and their limited use made them unappealing to modern families who may need a more versatile system. Thus, it is rare to see a boiler for radiant heat and hot water. Only a well-designed tankless water heater can provide such functionality.

How big of a water heater do I need for radiant heat?

On average, you need about 25 BTUs per hour for every square foot of floor space. For example, 100-foot floor space will require about 2,500 BTU per hour. Hence, you may have to calculate the space in each room you want to heat. You can then add each load factor to obtain your house’s total radiant heat requirement.

Let us say you have a two-story house with a basement. Your basement will require about 10 to 15 BTU/hour/sq. Ft.; you’ll also need 15 to 20 BTU/hour/sq. ft. for the first floor, and 20 to 25 BTU/hour/sq. ft. for the second floor.

Suppose you need to heat 100 sq. ft. of your basement, 500 sq. ft. on the first floor, and 400 sq. ft. on the second floor. Let us use the higher BTU range limit. Computing, we get 1,500 BTUs (15×100) for the basement, 10,000 BTUs (20×500) for the first floor, and 10,000 BTUs (25×400) for the second floor. You will need a water heater that can produce at least 21,500 BTUs every hour.

What is the most energy efficient water heater for radiant floor heat?

According to floor heating experts, condensing water heaters for hydronic heating are the most efficient. A propane water heater for radiant floor heat with condensing technology improves energy efficiency by an additional ten percent. These devices condense the exhaust steam and return the heat to the water.

As for the water heater type, tankless systems are more efficient than storage tank versions. According to the US Department of Energy, a tankless in floor heating water heater is free of standby energy losses because it only heats the water when needed.

The system does not store the water in tanks, which increases the potential for heat and energy loss with prolonged standby times.

The market offers many energy-efficient infloor hot water heating systems. For example, the EcoSmart ECO 18 electric on-demand water heater can help households save 50% of their energy expenses with its self-modulating technology, despite running on 18 kilowatts.

Stiebel Eltron’s Tempra 20 Plus electric water heater is also worth considering. It has a 99% Uniform Energy Factor, despite requiring 19.2 kilowatts. Although its efficiency is distant from hybrid systems’ 2.75 to 3.5 UEF, a 0.99 UEF is still commendable, especially compared to a gas water heater (UEF 0.5-0.7).

What size tankless water heater do I need for in-floor heat?

No standard size for concrete heating floor with water heater exists because this will depend on the BTU requirements and floor size. As a rule, you can allot 25 BTUs per hour for every square foot.

Basements require 10 to 15 BTUs per hour per square foot. First-floor spaces need about 15 to 20 BTUs, while second-floor areas demand 5 more BTUs per hour per square foot. These guidelines should help you determine the most appropriate size when using a water heater for radiant heat.

Suppose you want to heat a 300-square-foot basement, a 1,200-square-foot first floor, and a 1,500-square-foot second floor. Let us also assume you want the highest BTU rating for each space (i.e., 15, 20, and 25 BTUs).

In that case, the basement needs 4,500 BTUs; the first floor requires 24,000 BTUs; and the second floor demands 37,500 BTUs. Adding these figures results in 66,000 BTUs per hour.

You might want to buy a tankless boiler for radiant heat with at least a 66,000 BTU/hour rating. It should be sufficient to warm your home’s interior. You can always go for a tankless water heater with a higher BTU for peace of mind.

What is the best water temperature for radiant floor heat?

The ideal water temperature to achieve radiant floor heat is between 85 and 140 degrees Fahrenheit, lower than baseboard hydronic systems (130 to 160 degrees Fahrenheit).

You can use a propane boiler if you live in areas with high electricity prices and low natural gas costs. Meanwhile, families wary of gas problems might want an electric boiler to deliver the ideal water temperature for their radiant floor heating.

Households might want to maintain the ideal temperature to guarantee adequate space heating, regardless of the heat source.

Is radiant heat cheaper than electric?

Yes, radiant heat is cheaper than electric floor heating systems. After all, electricity is expensive, averaging about 16 cents per kilowatt-hour. The most expensive rate is in urban Hawaii at 45 cents/kWh, while the cheapest is in St. Louis at 12.7 cents/kWh. Although most radiant heaters also use electricity, they are less costly to operate.

Radiant floor heaters’ biggest advantage is their ability to heat the entire house. Electric versions can also elevate room temperature, but only by a few degrees. They also “warm” only the area with electrical heating cables. Meanwhile, radiant heaters “heat” adjacent spaces without requiring additional in-floor modifications.

On a side note, are you wondering which is cheaper and more cost-effective, a boiler vs a water heater for radiant heat? Water heaters are more affordable than boilers. Including unit price and labor costs, water heaters can cost families $1,000 to $3,5000, while boilers require a $3,500 to $8,000 budget.

Water heaters are also more cost-effective because you can use hot water to warm the floor, cook food, and make your favorite hot beverages. Meanwhile, boilers produce non-potable water. You can only move the hot water through the PEX tubing under the floor to heat the living space.


The best water heater for radiant floor heat provides your family with more significant energy savings than any other space-heating technology. It is efficient, noiseless, and versatile enough to deliver hot water to your shower, kitchen, and washroom. Our comprehensive review and buying guide empower you to pick the right system to heat your floor efficiently and cost-effectively.

5/5 - (2 votes)