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The History of Underfloor Heating Technology

The History of Underfloor Heating Technology

The electric radiant floor heating you find in many homes these days has come a long way. Did you know that underfloor warming has been around since nearly 5,000 B.C.? These primitive methods weren’t nearly as advanced as a SunTouch or NuHeat system, but the core concept of radiating heat  in the floor hasn’t changed.

The earliest examples date back to ancient Korea and Manchuria, where fires were built in stone-covered trenches below primitive dwellings. The stones would then heat up and radiate heat into the rooms above, while the smoke would pass through to a chimney located outside the house. Known as an “ondol” or sometimes “gudeul” system, this technology evolved into a structure where the fire was used both to heat the floor AND a kitchen stove.

Perhaps the most famous example of early floor warming comes from the Ancient Romans and Greeks and the so-called “Roman Baths.” In addition to heating baths, “hypocaust” technology was used to heat homes and buildings, both public and private. Since the system required constant attention to a fire furnace, and could become expensive with fuel costs, it was seen primarily in upper-class villas and public baths.

Hypo, meaning “under,” and caust, meaning “burnt,” relates to a fairly advanced system of underfloor heating. The house was built on several rows of pillars with the floor being a layer of concrete sandwiched between two layers of tiles. This basement area was called the “caldarium” and is where the baths were commonly located. The furnace was located at one corner of the caldarium and was usually built under the master bedroom or kitchen. The building would also feature empty spaces or hollow bricks in the walls so the smoke could rise up out of the roof without polluting the inside of the house.

Although these two systems are quite similar, hypocaust is generally considered the Western form of floor warming, while ondol is native to Eastern civilizations. Hypocaust technology spread as far as Turkey, Iraq, and Algeria, while Ondol continued to be popular throughout all of Asia. After the decline of the Roman Empire, hypocaust systems evolved into the Gloria system, which had a slower rate of combustion and allowed for smaller and cheaper fuels such as hay.

As you might imagine, the biggest problem with these primitive underfloor heating techniques was carbon monoxide poisoning, caused by fumes leaking through the floors. By the 19th century, many ondol, Gloria, and hypocaust systems had been replaced by early types of water boiling-based systems. In the 20th-century many new forms of radiant heating emerged, such as that seen in Frank Lloyd Wright’s famous line of Usonia homes. Today, underfloor heating can be divided into electric and hydronic systems.

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