What is Radiant Heating?

Archaeological evidence from China and Korea reveals the earliest known underfloor heating systems. The kang (heated bed-platform) and dikang (heated floor) used fires to channel hot smoke and gases through flues under masonry floors before exiting chimneys, creating radiant warmth from below.

These systems predate Roman technology by thousands of years, proving that the principle of radiant floor heating is one of humanity's oldest heating innovations.

Source: Encyclopedia Britannica

The Korean ondol ("warm stone") represents a highly refined version of ancient radiant heating. The kitchen firebox (agungi) was set lower than the floor, and a system of underfloor passages drew smoke and heat across the entire room, warming the stone floor which then radiated heat upward. This elegant design would later inspire Frank Lloyd Wright.

The ondol system has been continuously used in Korea for over 2,000 years, making it one of the longest-lasting heating technologies in history.

Source: UNESCO

With the fall of the Roman Empire in the 5th century, hypocaust systems gradually fell into disuse across Europe. The sophisticated engineering knowledge was largely lost during the Middle Ages. People returned to simpler heating methods—fireplaces, hearths, and later stoves—which couldn't match the even, radiant warmth of the hypocaust.

While some Byzantine structures in the Eastern Roman Empire may have maintained hypocaust systems for a time, the technology essentially disappeared from Western Europe for nearly a millennium.

Source: Journal of Roman Archaeology

This century saw adaptations of stoves and flue systems rather than a true revival of the hypocaust. In Northern and Eastern Europe, the Kachelofen (tile stove) provided radiant heat through massive thermal mass. In French greenhouses, builders ran flue pipes from furnaces under floors to protect plants from frost—a technique noted by English diarist John Evelyn (1691), who speculated it might be a surviving technique from classical times.

These innovations kept the principle of radiant heating alive, even if the technology remained primitive compared to ancient systems.

Source: John Evelyn's Diary (1691)

The first major application of a hydronic (hot water) heating system is credited to Russia. Peter the Great's Summer Palace in Saint Petersburg featured a heating system, thought to be designed by Swedish engineer Mårten Triewald, that used a central boiler to heat water and distribute it through pipes.

This marked the beginning of using water as a medium to transport heat, the foundation of modern central heating.

Source: Swedish Royal Palaces

Scottish inventor James Watt, famed for his improvements to the steam engine, built a rudimentary steam-based central heating system for his own house. In 1793, English engineer William Strutt designed a "cockle stove" furnace for his textile mill in Derby, England, that heated air in a central furnace and distributed it via ducts—a forerunner to modern forced-air systems but with radiant properties from the warm ducts.

These innovations demonstrated that steam and warm air could distribute heat throughout buildings, setting the stage for the radiator revolution.

Source: Engineering Timelines

American engineer Angier March Perkins (working in the UK) patented a high-pressure hot water heating system using small-bore wrought-iron pipes. This was more efficient and allowed pipes to be routed more easily than the large, low-pressure pipes used previously, making central heating more practical.

Perkins' innovation made hot water systems viable for larger buildings and more complex installations.

Source: US Patent Office

A rudimentary form of radiant floor heating was reportedly used in some Civil War field hospitals. A fire pit was dug outside a tent, and a trench covered with sheet iron ran through the tent to a chimney, radiating heat upwards to warm the wounded.

This practical application demonstrated that even simple radiant heating could provide comfort in challenging circumstances.

Source: Civil War Trust

British engineer Prof. Arthur H. Barker patented a "panel warming" system after calculating that embedding small hot water pipes directly into concrete floors or plaster walls would be an efficient heating method. This marked the true rebirth of radiant floor heating, inspired by ancient Asian systems.

In 1909, Barker's company, R. Crittal & Company, installed his system in the iconic Royal Liver Building in Liverpool—one of the first large-scale modern applications of hydronic radiant floor heating.

Source: Engineering Timelines

While working in Japan on the Imperial Hotel, American architect Frank Lloyd Wright experienced a Korean ondol room and was captivated by the "indescribable warmth" that came from the floor. This firsthand experience would profoundly influence his future architectural designs.

Wright's exposure to ancient Asian radiant heating technology would shape his approach to modern American architecture.

Source: Frank Lloyd Wright Foundation

Wright brought his ondol inspiration to America, incorporating hydronic "gravity heat" into his first "Usonian" house in Wisconsin—the Herbert Jacobs House. He ran wrought-iron pipes in a gravel bed beneath the concrete floor slab, allowing the entire floor to act as a gentle, low-temperature radiator. He believed this was a more natural and comfortable way to heat a space.

This design demonstrated that radiant floor heating could be both functional and aesthetically elegant, eliminating the need for bulky radiators or ductwork.

Source: Frank Lloyd Wright Foundation

Radiant floor heating became popular in tract housing developments like Levittown, New York. However, these systems often used copper or steel pipes directly embedded in concrete. Problems with corrosion and leakage over the next 20 years gave the technology a bad reputation in North America.

Despite initial popularity, material failures threatened to end the radiant heating revival before better solutions could emerge.

Source: National Park Service

The technology was saved by the invention of cross-linked polyethylene (PEX) tubing, patented by Thomas Engel. PEX is a flexible, durable, and non-corrosive plastic pipe that made hydronic radiant floor systems reliable, affordable, and easy to install.

This breakthrough led to the widespread resurgence of radiant floor heating in modern construction, solving the corrosion problems that plagued earlier systems.

Source: US Patent Office

Electric radiant heating technology begins to mature with improved cable designs and better integration with floor coverings. Early adopters recognized the potential for affordable, easy-to-install heating that worked with any flooring type—no boilers, pumps, or complex plumbing required.

This breakthrough combined ancient principles with modern technology, making radiant heat accessible without the complexity of previous systems.

Julia Billen begins working with electric radiant heating technology, recognizing its transformative potential for homeowners. Her vision: make the comfort of radiant heat accessible to everyone, not just new construction projects.

This personal commitment to accessibility would shape the future of electric radiant heating.

Julia founds WarmlyYours Radiant Heating with a mission to make floor heating accessible, affordable, and easy to install. The company introduces DIY-friendly installation guides, responsive customer support, and products designed for real homes.

This marked a shift toward making radiant heating mainstream, not just a luxury for the few.

Electric floor heating gains popularity as homeowners discover its benefits: zoned comfort, energy efficiency, and compatibility with any flooring type. Installation becomes simpler with pre-spaced mats and flexible cable systems.

The technology transitions from niche to mainstream as more homeowners experience the comfort of radiant warmth.

WiFi-enabled smart thermostats transform electric radiant heating into an intelligent system. Homeowners gain precise control, energy-saving schedules, and remote access through smartphone apps. Floor sensors provide accurate temperature readings for optimal comfort.

Integration with home automation systems brings radiant heating into the connected home era.

Electric radiant floor heating has become a mainstream comfort upgrade. Today's systems feature ultra-thin heating elements that install under virtually any flooring, advanced smart controls, and energy-efficient designs. From luxury resorts to everyday homes, radiant warmth provides the ultimate in comfort while reducing energy consumption.

The culmination of over 2,000 years of innovation—from the Baths of Caracalla to your home—proving that the best heating solutions stand the test of time.