Can Tankless Water Heater Be Used for Radiant Floor Heat? Pros and Cons

Imagine stepping onto a warm, heated floor in the chilly winters. A luxurious treat, isn’t it? However, most homeowners still rely on traditional heating systems which might not deliver this delightful experience. Herein lies a question that you might have mulled over: Can a tankless water heater be used for radiant floor heat?

According to a study by the U.S. Department of Energy, traditional water heaters account for nearly 17% of a home’s energy use. However, tankless water heaters, also known as “on-demand” units, can drastically cut energy consumption, giving you more bang for your buck.

This post uncovers a potential game-changer for your home’s heating strategy. It delves into the use of tankless water heaters for radiant floor heating, unravelling the pros and cons, and enlightening you on how this upgrade could revolutionize your home heating experience. Buckle up for a deep dive into a potential solution that promises warmth, efficiency, and cost savings.

Keynote: Can Tankless Water Heater Be Used for Radiant Floor Heat?

Yes, tankless water heaters can be used for radiant floor heating. They provide on-demand hot water efficiently, saving energy. However, installation complexity and the need for a model with sufficient BTUs are key considerations. Always consult a professional for a suitable setup

Tankless Water Heaters

Tankless water heaters, in the words of James Brew, a leading Energy Expert at the National Renewable Energy Laboratory, “are compact, highly efficient units that provide hot water on-demand without the need for a storage tank.” Brew further states, “They heat water directly, only when you need it, resulting in significant energy savings over traditional water heaters.”

How Tankless Water Heaters Work

Unlike traditional water heaters that keep gallons of water heated in a tank, tankless water heaters only heat water when you turn on the tap. They use a heat exchanger that gets activated by the incoming flow of water, heating the water to the preset temperature. This on-demand heating provides hot water instantly without any wastage.

Types of Tankless Water Heaters

There are mainly two types of tankless water heaters:

  1. Electric Tankless Water Heaters: These heaters use electricity to heat the water. They are typically smaller and less expensive but may require a significant amount of electricity.
  2. Gas Tankless Water Heaters: These use propane or natural gas to heat the water. They can produce a larger volume of hot water and are ideal for big households.

Pros and Cons of Tankless Water Heaters

Like any technology, tankless water heaters have their pros and cons. Here’s a brief overview:



  • Higher upfront cost: They are generally more expensive to purchase and install than traditional water heaters.
  • May require upgrades: Electric models may require a home’s electrical system to be upgraded. Gas models may need a larger gas line or an additional ventilation system.
  • Inconsistent temperature: If multiple appliances are in use, the temperature of the water may vary.

Radiant Floor Heating

Radiant floor heating is a method of warming a home that is growing in popularity. As Adrian Tautscher, Senior Technical Manager at JG Speedfit, describes, “Radiant floor heating involves directly heating the floor of a house to provide warmth, creating an efficient, evenly-distributed, and comfortable heating system that replaces the need for traditional radiators.”

How Radiant Floor Heating Works

Radiant floor heating operates on the principle of thermal radiation. It warms objects in a room rather than the air. Essentially, heating elements (electric wires or water tubes) are embedded or placed under the floor. These elements heat the floor surface, which in turn radiates heat upwards into the room, providing consistent, efficient warmth.

Types of Radiant Floor Heating Systems

Radiant floor heating systems primarily fall into two categories:

  1. Electric Radiant Floor Heating: This system uses electric resistance cables to produce heat. It’s commonly used in single rooms, especially in renovations or bathrooms.
  2. Hydronic Radiant Floor Heating: This type involves running hot water through plastic PEX tubes beneath the floor. It’s considered highly efficient for heating larger spaces or entire homes.

Pros and Cons of Radiant Floor Heating

As with any heating system, radiant floor heating has its own set of advantages and disadvantages.


  • Energy Efficiency: These systems can use less energy than conventional heating methods, reducing your energy bills.
  • Comfort: They provide consistently, even heat without cold spots.
  • Quiet Operation: Radiant heating is virtually silent, unlike forced-air systems that can be noisy.
  • Versatility: Can be installed under a variety of floor coverings, including tile, wood, and carpet.


  • Installation Cost: The initial cost can be higher due to the complexity of installation, especially in retrofit situations.
  • Time to Warm Up: The system can take a while to heat the room.
  • Changes: Any future changes or repairs to the system can be disruptive as it is embedded in the floor.
  • Floor Coverings: Not all types of floor coverings are suitable for radiant heat. Some insulating materials can reduce system efficiency.

The Compatibility of Tankless Water Heaters and Radiant Floor Heating

How These Two Systems Can Work Together

Tankless water heaters and radiant floor heating can work together to provide an efficient and comfortable heating solution. The tankless water heater, with its on-demand hot water provision, serves as a heat source for the radiant floor heating system.

When the radiant floor system calls for heat, it triggers the tankless unit, which quickly heats the water. This hot water then circulates through the PEX tubing embedded in the floor, radiating warmth into the room. The result is a continuously comfortable, evenly heated living space.

Requirements for Integrating Tankless Water Heaters with Radiant Floor Heating

Before integrating these two systems, several factors need to be considered:

  1. Size of the Heater: The tankless water heater should have enough capacity to meet the demands of the radiant floor heating system and household hot water needs.
  2. Temperature Controls: Some tankless water heaters may require a mixing or thermal bypass valve to ensure that the water entering the radiant floor system is not too hot.
  3. Power Source: Electric or gas? This depends on the availability and cost of these utilities in your area.

Key Considerations When Combining These Two Systems


  • System Compatibility: Not all tankless water heaters are designed to work with radiant floor heating systems. Ensure the models you select are compatible.
  • Heating Demand: Factor in the size of the space to be heated and the climate. These factors will influence the heater size and the type of radiant floor system.
  • Installation and Maintenance: Both systems require professional installation and regular maintenance to ensure optimal performance and lifespan.
  • Cost: While these systems can offer long-term energy savings, the upfront cost may be significant. Consider your budget and potential return on investment.
  • Local Regulations: Always check local building codes and regulations before installing these systems.

Advantages of Using Tankless Water Heaters for Radiant Floor Heating

Energy Efficiency

Integrating tankless water heaters with radiant floor heating can significantly boost your home’s energy efficiency. According to the U.S. Department of Energy, tankless water heaters can be 24%–34% more energy efficient than conventional storage tank water heaters in homes that use 41 gallons or less of hot water daily. Pairing this with the inherent efficiency of radiant floor heating – which, according to the National Association of Home Builders, can save 20%-40% in heating bills – you’re looking at substantial energy and cost savings.

Space-saving Benefits

Tankless water heaters are compact units that can be installed in various places, including closets, basements, or even on outdoor walls. This, coupled with the invisible nature of underfloor heating (which eliminates the need for bulky radiators), opens up more usable space in your home.

Longevity and Durability

Tankless water heaters have an estimated life expectancy of more than 20 years – almost double the lifespan of traditional tank-style heaters. Similarly, when installed and maintained properly, radiant floor heating systems can last decades, providing you with long-lasting, reliable warmth.

Comfort and Consistency of Heat

When it comes to the comfort and consistency of heat, a testimony from Julia, a homeowner in Seattle, sums it up perfectly. “Since we’ve integrated our tankless water heater with our radiant floor heating, our home has never felt more comfortable,” she says. “The heat is evenly distributed, and it feels so cozy, especially in the winter. Plus, we’ve noticed a significant decrease in our energy bills. It’s been an absolute game-changer for us!”

Disadvantages of Using Tankless Water Heaters for Radiant Floor Heating

Initial Installation Cost

The upfront costs of integrating tankless water heaters with radiant floor heating systems can be substantial. As per HomeAdvisor, the average cost to install a tankless water heater ranges from $1,470 to $2,510, while radiant floor heating installation can range from $10 to $20 per square foot, depending on the type of system and the complexity of the installation. While these systems can offer significant long-term savings, the initial investment may be prohibitive for some homeowners.

Complexity of Installation

Both tankless water heaters and radiant floor heating systems require professional installation, adding to the cost and requiring you to find a knowledgeable and experienced installer. Additionally, retrofitting a home with radiant heating may involve substantial changes to the flooring, which can be disruptive and time-consuming.

Maintenance and Repair Considerations

Tankless water heaters require regular maintenance, including annual descaling, to remove mineral build-up. Likewise, while radiant floor heating systems are generally low-maintenance, any repairs that do need to be made can be complicated and costly, particularly as the system is embedded in the floor.

Potential Limitations or Challenges

While these systems generally work well together, there can be challenges. Tim, a homeowner in Boston, shares his experience: “We installed a tankless water heater with radiant floor heating in our home. While we enjoyed the consistent heat, we had some initial problems. Tankless unit wasn’t sized properly to handle our domestic hot water needs and the radiant heating system, which meant we didn’t always have hot water when needed. We ended up needing to upgrade to a larger unit. Make sure to factor in both needs when considering this setup.” This highlights the importance of correct sizing and professional installation when integrating these systems.

Final Thoughts

At first glance, the integration of tankless water heaters with radiant floor heating might seem like a complex endeavor. However, the end result – a cozy, energy-efficient home – certainly justifies the investment for many homeowners. This modern approach to home heating takes the best of both worlds, coupling the on-demand convenience and energy savings of tankless water heaters with the comfortable, consistent heat of radiant floor systems.

However, like any home improvement decision, it’s important to consider the unique characteristics of your home and lifestyle. Weighing the initial cost against long-term savings, understanding the installation complexities, and ensuring you choose the right equipment for your needs are critical steps in making an informed decision.

Ultimately, when done correctly, this innovative combination presents a sustainable way of heating our homes, demonstrating how technology can be harnessed to create comfort, increase efficiency, and shape a greener future.

Tankless Water Heater for Radiant Floor Heat (FAQs)

Can a tankless water heater be used for hydronic heating?

Yes, a tankless water heater can indeed be used for hydronic heating. The system circulates hot water through the heating elements such as radiators, baseboards, or underfloor pipes, which then radiate the heat to the room.

Can you use a tankless water heater for baseboard heating?

Definitely, a tankless water heater can supply hot water to baseboard heaters. It heats water as it flows through, providing a continuous supply of hot water to the baseboard heating system.

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

The size of a tankless water heater for in-floor heat depends on factors such as the size of your home and the climatic conditions. Generally, for a standard-sized home in a moderate climate, a heater with 150,000 to 200,000 BTU may be sufficient.

Can a tankless water heater handle the heating demands of a large radiant floor system?

A tankless water heater can handle the heating demands of a large radiant floor system, but its efficiency can be influenced by factors like the system’s design, the ambient temperature, and the insulation of your house. It is crucial to size the heater correctly to meet the system’s demands.

Can a tankless water heater be retrofitted into an existing radiant floor heating system?

Yes, a tankless water heater can be retrofitted into an existing radiant floor heating system. However, it’s essential to consult with a professional to ensure the heater’s capacity matches the system’s requirements and to ensure correct installation.

Does hard water affect the efficiency of a tankless water heater?

Yes, hard water can lead to sediment buildup in a tankless water heater, which may reduce its efficiency and potentially cause damage over time. A water softener can help alleviate this issue.

How does a heat pump work in a hydronic system?

A heat pump in a hydronic system absorbs heat from the air or ground and uses it to heat the water. The heated water then circulates through the radiant system, providing warmth to the space.

What is the role of a vent in a gas-fired water heating system?

In a gas-fired water heating system, the vent safely expels combustion byproducts, including carbon monoxide, outside of the house, ensuring safe and efficient operation.

How does the warranty on an electric water heater like Stiebel Eltron typically work?

The warranty on an electric water heater like Stiebel Eltron typically covers defects in materials or workmanship for a specified period. It’s crucial to review the warranty terms for specifics, as certain conditions or maintenance requirements may apply.

Does the flow rate affect the water temperature in a tankless system?

Yes, the flow rate directly impacts the water temperature in a tankless system. A high flow rate might result in lower water temperatures because the heater has less time to heat the water as it passes through.

Can an electric boiler be used in conjunction with a radiant floor system?

Absolutely, an electric boiler can efficiently supply heated water for a radiant floor system. The boiler heats the water, which is then circulated through pipes embedded in the floor slab, providing a comfortable and evenly distributed heat.

Can a Takagi on-demand water heater provide a substantial amount of heat over a long time?

Yes, a Takagi on-demand water heater, if sized appropriately, can continuously provide a substantial amount of heat for as long as hot water is needed. Its capacity is often measured in gallons per minute (gpm).

Is a hot water heater more efficient than a furnace for a home’s heating system?

While both can be part of a home’s heating solution, a hot water heater and a furnace serve different purposes. Furnaces directly heat air for space heating, while hot water heaters supply hot water for use in appliances or hydronic heating systems. The efficiency depends on the specific models and their usage.

Is it necessary to hire a plumber to install an on-demand water heater?

While some homeowners might feel comfortable with a DIY approach, hiring a professional plumber to install an on-demand water heater is generally recommended. This ensures the plumbing is correct, enhances safety, and often safeguards the manufacturer’s warranty.

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