What is Radiant Heating?

Ancient, Efficient, Practical, and Cozy

** Updated July 6th, 2022. Originally posted March 9th, 2022.

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Radiant Heating & Cooling

John Webb has been a highly reputable new home builder in Eugene Oregon for 20 years. The John Webb Construction & Design team are well known for building new energy efficient homes. The literal foundation of his reputation starts with Radiant Heat floors. Learn about the history and design principles of radiant heating and cooling.

What exactly is Radiant Heating and Cooling? Or, if you happen to know what it is and find that there really is no better way to heat and cool your home, your question is likely: Why isn’t it more common?

A heating and cooling system is considered radiant if it’s heat exchange is over 50% radiation. Baseboard heaters for instance, radiate a lot of heat, require a ton of energy, and are so inefficient that the gradual convective action (90%) has to fill the room from the top down to provide comfort. Radiant Heating and Cooling uses efficiently placed, larger radiators of varying types (Electric, Infrared, and Hydronic) to create and utilize a larger thermal mass for the heating and cooling of a space. There are a surprising number of fascinating design options for Radiant Heating & Cooling for indoor & outdoor commercial and residential applications. For this post we will focus on hydronic residential underfloor systems and give a quick overview of the history of this technology.

What does Hydronic Mean? How it works in Residential Construction

Residential Underfloor Radiant Heat systems often use Hydronic technology. Hydronic Radiant Systems use temperature-controlled water that is pumped through hundreds of feet of pipes and tubing. Hydronic Systems tend to be of two types:

  • Embedded Surface Systems – Embedded in the surface layer of the flooring. There are a couple ways to design such systems and are often installed during a remodel when the owner wants to upgrade their HVAC system. Bathrooms with heated tile upgrades are a perfect example of an embedded surface system.
  • Thermally Active Building Systems – Sealed inside the concrete foundation of a home. These are the most efficient option as they take advantage of the largest thermal mass in a home to achieve maximum comfort while using less energy than other systems.
Type E Hydronic Radiant System
Radiant Heat Tubing Prior to Concrete Pour at the Hatfield Project

the Energy Efficiency of Radiant Heating Systems

More precise temperature control is the most obvious benefit of a well designed radiant heating and cooling system. Your standard forced-air system rely’s on a thermostat that is mounted chest-level on an interior wall. This means that the air at 4 feet is at 70 degrees while the air below the thermostat is cooler. A Hydronic system controls the temperature of the water inside the floor itself, making micro-adjustments to the boiler output, distributing that water out through several pumps to the different zones within the system, ensuring that the entire home is warmed (or cooled) from the floor on up. This allows you to set your temperatures lower to achieve your standard of comfort.

Installing the Insulation Layer for the Hatfield Project Radiant Heat Slab
Notching the Hatfield Project Radiant Heat Slab to Resemble Large Tiles

the Ancient Origins of Radiant Heating

The history Radiant Heating is actually quite surprising. Accomplished Modernist Architects and Developers like William Levitt, Joseph Eichler and of course Frank Lloyd Wright, helped to popularize Radiant Heating and Cooling systems in the West. When they were integrating these rather practical ideas into their residential designs it was believed that Radiant Heating & Cooling in architecture was possibly 1000 -1500 years old. It turns out you have to travel as far back as 10,000 BCE, to China and the Korean Peninsula, to understand it’s origins.

A Quick Timeline of the History of Radiant Heating in Architecture

  • Originally, a rudimentary version of these systems, called Ondol, included flukes running through a home’s foundation, heating the home. Written evidence refers to these designs as far back as 10,000 BCE. There is archeological evidence of a handful of dwellings that contained a version of these designs between 5000 and 1000 BCE in China, the Korean Peninsula, and as far out as the Aleutian Islands in Alaska.

  • Over the course of several millennia an increasing number of homes would have 2 fire hearths, or furnaces: 1 for cooking and 1 for heating. – There is evidence that this technology made it’s way to Greece and Rome around 500 BCE, where they would condition floors and walls in larger structures, calling it Hypocaust.
  • Around 700 CE, the people of Iraq, Algeria, Turkey, and Afghanistan learn how to apply these principals to their architecture.
  • Back in Asia, in order to achieve higher temperatures while also protecting the health of the occupants of a home, the heating furnaces were relocated to outside.
  • – Around the year 1,000 CE the modern fireplace & chimney system starts to become the norm in Europe.
  • The first documented use of cooling pipes used in architecture was in Lotus Mahal, Hampi, Karnataka, India around 1540.
  • A one Cornelius van Drebbel was born in Holland in 1572. He is credited with inventing automated temperature control.
  • In the early 1700’s systems utilizing steam are used in France. Benjamin Franklin starts developing the Franklin Stove after studying French and Asian Radiant Heat systems.
  • In the early 1800’s the modern water heater/boiler and adequate piping is under development in Europe.
  • In 1905 Frank Lloyd Wright visits Japan where he picks up and later incorporates his understanding of Radiant Heating & Cooling into his architecture.
  • In 1908 A.M. Byers of America, a pipe manufacturer, encourages developers to use small pipes filled with water embedded in floors and walls, for the heating of structures.
  • In 1945 American developer William Levitt launches the largest scale development using Radiant Heat systems for returning Military Services Members. Due to poorly designed and inadequately sealed systems and homes, injuries and illness result.
  • In 1950 Joseph Eichler starts construction on thousands of homes in California with Radiant Heating systems. Learning from William Levitt’s mistakes, the Eichler homes had far more efficient and healthier designs.
the Hatfield Project - Hydronic System Engineering Plans

For most of the 20th Century, before the technology was there, when residential development was less concerned with the health and safety of residents, a number of mistakes were made in designing and installing these systems. In the late 70’s poorly designed Radiant Heat systems that used coal and flue gas in apartment buildings in Korea, resulted in death and sickness. Such tragedies inevitably led to higher regard for safety and the need for technological advancements and reconsiderations. Over the course of the 1980’s it was established that Hydronic Systems were the safest and most efficient option for Radiant Heating & Cooling.

Back Home in Oregon - Bringing a Modernist take on Ancient Tech

John Webb’s standards when building his signature energy efficient homes starts with a Radiant Heated, polished concrete slab. When exactly did this become John’s foundation of efficiency?

In the late 70’s, while John was gaining Architecture & Design experience in Terra Linda, California, he lived in an Eichler Home. Joseph Eichler, a renowned modernist developer, designed quite a few homes in the San Rafael area with walls of glass, open-beam ceilings, and radiant heat floors. Living in such a unique home at the beginning of his career, John was able to see the stylistic and practical appeal of those design choices, and picked up on the clear differences between forced air and radiant heated homes.

The Architecture & Design Firm John worked for built homes in Lake Tahoe and Park City, Utah, all with Radiant Heating. Seeing how well these residential heating systems performed in such cold environments really sold John on the technology. You really can’t argue with warm feet on a bare floor, a significantly lower heating bill, a silent heating system, and not having to deal with the dust that forced air systems draw in and kick around your home. Once John was designing & building homes for clients, he knew radiant heat systems would be the right choice for nearly all of his clients.

the Health Benefits of Radiant Heating Systems

Polished Hydronic Heated Slab for the Hatfield Project

Radiant Heat systems help to create a far healthier home environment in several ways. 

  • Cuts down on moisture. The even, floor-up heating drastically reduces moisture and condensation on windows and walls, limiting the potential for mold and moisture damage throughout your home.
  • Much easier to clean. When you, your children or pets come in out of the rain, bringing water and mud, the floor dries itself in a matter of minutes. 
  • Far less dust in your home.  Eliminating or reducing dependence on forced air systems means less dust is being pumped into the home.
  • Less reliance on carpet for comfort means less dirt and germs are collecting in entryways, getting kicked up throughout the summer months and less mud taking too long to dry and clean up in the winter months. Being able to eliminate unsightly entryway carpeting is a game changer.

Advances and Limitations of Radiant Heat Technology

Radiant Heating & Cooling systems have become quite advanced over the last 40 years. Considering that these systems are installed for reasons of energy efficiency, health, and comfort, they often work in conjunction with air filtration, dehumidification, and central air systems. For hydronic systems, in the warmer months, to run cooler water through your foundation will drastically cut down on the output needs of your AC system. There are of course limitations to any technology. Depending on the average relative humidity and overall climate of where you live, your heating and cooling needs will vary. The nearer you are to the equator the greater your reliance on your hydronic system’s cooling. Due to the resulting condensation from more extreme system settings, you will need a more robust dehumidification system.

Radiant Heating & Cooling –The Ultimate In Energy Efficient New Home Construction

Gosh I think it must have been back in the late Seventies, I had lived in Terra Linda California, in an Eichler Home which is all walls of glass and open beam ceilings – very simply built – and they all had radiant heat floors. That was really my first experience living in it and having that in the winter time. I really loved the way that the heat was all even and silent with no dust in the whole thing.

That is something that I really had to design into my own buildings when I went out on my own. When I was working in the Architecture and Planning Firm we used Radiant Heat designs when we built homes up in Lake Tahoe and Park City Utah. They were all Radiant Heat since they were in a much colder climate. Almost all the homes I’ve built have that option in them.

You know, they’re really very healthy homes. They don’t have all of the dust blowing around that more conventionally heated homes have. It’s nice for dogs running in and out in the wintertime, the floors dry, and you just dust it, or sweep it up. Whether they come in with muddy feat it doesn’t matter, it dries quickly and you just use a dust mop or vacuum and clean it right up. It’s wise.

It’s just a different kind of heat. All your forced air thermostats are at about 4 feet high, so if it’s set for 70, everything above it is 70 degrees and everything below it is cooler. So, the difference is that the heat is coming from under your feet so you can set your thermostat lower and it’s even. You don’t have any cold spots. Say you have walls of glass, it’ll be an even heat throughout the entire place.

And we’ve gotten a bit more sophisticated with it. All our shower floors are radiant heated. In the Summertime the floor is cooler – the cool air created by the concrete slab stays closer to the floor, which seems to me and is proven by your electricity bill, that it’s more energy efficient that way. It’s cooler when you want it in the Summer and it’s really warm and nice and cozy in the Winter.”

Written by Todd Zimmerman

Producer of the John Webbccast