Explaining the Incomparable Comfort of Radiant Heat

April 16, 2025/in Blog/by Hoyt Corbett

“You Can Feel It”: The Unspoken Comfort of Radiant Heat

“It is not warm air that makes you comfortable, but warm everything.” — James Cutler, Faia

“You can feel it the moment you walk into a room.” — Hilary Mackenzie, AIA

“Tell them it’s like the sun indoors.” — John Fantauzzi, Industry Innovator

More than 20 years ago I had the privilege of interviewing two well-known West Coast architects about their choice of radiant heating for their award-winning custom projects. Each had evolved their own vocabulary around the distinctive comfort of radiant heat, a comfort best explained by the concept of mean radiant temperature.

“You can feel it,” explains architect Hillary Mackenzie. “I have always tried to make ever better houses and buildings for my clients, and the quiet, even heat of radiant floors fits that goal. I have never had a client who didn’t love it… the comfort has a feel-good quality that is hard to describe in words, but you can feel it the moment you walk in the room.” ….So rather than simply describing the advantage of radiant heat, I recommend taking potential clients to a radiant floor-heated home, and let them feel it.

Nationally renowned architect James Cutler went beyond description of the heat itself, to explain why you feel that special quality in homes heated by hydronic radiant floors. He explained that about 98% of a home’s warmth is inherent in the mass of objects filling the interior space and radiating from surfaces, while only 2% typically comes from the heat capacity of air itself: “It is not warm air that makes you feel comfortable, but warm everything.” Cutler also appreciated that the lack of obtrusive duct work allowed him to concentrate on the bones of a structure.

Home’s warmth using the concept mean radiant temperature

Photo Credit Art Grice Courtesy of Cutler Anderson Architects

The idea that with radiantly heated interiors, “the warm everything” is what makes you so comfortable is technically understood in the industry via the concept of Mean Radiant Temperature or MRT.

I used to say, “Premium homes deserve premium heat.” And then I’d explain MRT.

Mean Radiant Temperature refers to the average temperature of all the surfaces surrounding you, including walls, windows, floors, and ceilings, even cabinetry. It represents the combined effect of radiant heat coming from all these surfaces, all contributing to a person’s perception of comfort, whether warmth or coolness. Unlike air temperature (the temperature of the air around a person), MRT represents the radiant energy exchange between a person and surrounding surfaces.

Research on MRT, human metabolic rates, and comfort, has shown that—in most cases—people in a radiantly heated home are comfortable at lower air temperatures due to the higher average surface temperature near their bodies. Typically, in a forced air home, convection drives uneven air temperatures (heat rising, for instance), which results in uneven surface temperatures: the higher parts of a room are significantly hotter, whereas in a radiant floor heated home the heat begins beneath your feet and emanates everywhere.

In calculating MRT, it is typical to take into account the surface temperatures of various surfaces within the line of sight of the person, as well as the distance from these surfaces and their respective emissivity (how well they radiate heat). Clearly, these are not intuitive calculations, but they are of consequence: the results can be felt! Since the 3 dimensional computations are very complex it is hard to represent in a drawing. But it has been well confirmed with finite element analysis and thermal imaging.

Mean Radiant Temperature, Comfort and Energy Efficiency

There is a strong relationship between Mean Radiant Temperature and comfort in radiant floor heated homes, since most of the heat is transferred directly to a person, metabolic research has also shown that in a radiantly heated home, if the MRT is below 64°-68°F, a person will likely feel cold. If you are aiming for a comfortable space, you would usually want to keep the MRT around 72°-75°F for most people, which aligns with a neutral metabolic comfort zone for indoor settings. The gift of radiant floor heating is that, due to the average surface temperatures at body level being warm.

Because of MRT most people feel comfortable at a lower air temperature than with forced air heat because of all the warm surfaces radiating heat. In a radiant heated room, the ideal condition for comfort occurs when the MRT is balanced so that there is not a big difference between what a person feels from the surrounding surfaces, and the ideal metabolic comfort ranges referenced above. The air temperature can be lower, and people will still be comfortable, as long as the MRT is higher and more consistent (steady), which is usually the case.

So maintaining a lower air temperature (than a conventional forced air system requires) saves energy, aided by the small circulating pumps required for hydronic radiant heat, and the inherent efficiencies of using the denser medium of water, versus air, to transfer heat. Forced air systems usually involve significant duct losses, and require much more fan energy to blow compressible air through big ducts.

Think How the Sun Works

My friend John Fantauzzi—an early proponent of radiant heat and colleague in the Original Radiant Panel Association—suggested we tell potential clients: “Tell them it’s like the sun indoors.” When I was a radiant floor heating contractor, I hadn’t used such a brilliantly simple image, but did tell potential customers to do a similar thought experiment: “Imagine you’re basking on a warm beach on a sunny day, all that sand and air warmed by the radiant heat from the sun.” Or, more personally, I would recount my experience as a professor at the University of New Mexico in Albuquerque:

In winter, our nights would often go down to 25°F then climb to 40°F by mid day. On the south side of the building where I taught, there was a courtyard between my building and a reservoir that had a high enough wall to protect the courtyard from the wind, but still allowed direct sunlight. That south-facing adobe-colored wall absorbed solar energy, its warmth radiating into my back as I sat in front of it, while the sun itself sent its radiant rays to warm my front side, too. I discovered that in this space that was radiantly heated from the sun, I could be comfortable on a 40° morning in a t-shirt!

Later, when I moved to the drearier winters in the Puget Sound, I was determined to bring some of that radiant sunlight with me. I built a house sited with southern exposure, with radiant floor heating that was exceptionally warm and comfortable. Our radiantly heated floors made us feel we’d brought some of the New Mexico sun north with us.

In this home in the winter, on a cold day the radiant floor might be 78°F, but because the surfaces were all at a higher temperature than air temperature, we were almost always comfortable at 67°F-68°F air temperature in shorts and a T shirt.

There are many graphics (like the one shown below) that illustrate the how air temperature in a radiantly heated home is distributed significantly differently than that in most forced air interiors. These drawings make a good argument for the efficiency of radiant floor heating, and show the more even temperatures common with radiant heat, but they don’t explain it the way the concept of Mean Radiant Temperature does.

In a radiantly heated home, Mean Radiant Temperature is what determines thermal comfort because it reflects the heat exchanged from surrounding surfaces to a person. Since this is a dynamic process that takes into account the radiant energy coming from every surface, in every direction, it is best felt and understood as a large, even, low- temperature surface which, unlike forced air, has an even lower temperature profile. It is incredibly quiet, saves energy, and perhaps best of all, it’s incredibly comfortable.

ABOUT THE AUTHOR

Hoyt Corbett

Partner, Warm Brothers Inc.

Hoyt has been involved with hydronic heating since the early 1990’s and developed and sold a national brand of radiant floor heating that was acquired by Uponor. Subsequently, Hoyt was Associate Director of the Radiant Panel Association, the industry trade group.

He’s produced extensive technical writing on radiant floor heating, writing several major national hydronic vendor’s radiant heating design and installation manuals as well as founding and publishing The Radiant Flooring Guide.

Call Hoyt at 206-369-1458, 8am to 5pm PST

or

email him at: hoyt.corbett@warmbrothersinc.com

Hydronic Radiant Floor Heating Panel Types and Thermal Inertia

April 10, 2025/in Blog/by Hoyt Corbett

This blog is designed, in a commonsense way, to explain how different radiant panel types respond at different rates when charged with warm water. It will explore the applicable uses of different types of hydronic radiant panels and applicability of different controls to each type.

Example of a high mass hydronic radiant panel system in a slab followed by a low mass example attached to a subfloor Followed By An Example of A Low Mass, Low Thermal Inertia Radiant Panel System.

Radiant floor heating hydronic panels using a slab have a lot of thermal mass that must heat up or cool down to counter-act changing temperatures in a home or a building. A large mass of relatively dense concrete conducts the heat from the pipes to the surface which usually includes floor coverings from where it then radiates heat to the room.

Low mass, low thermal inertia panels are usually made by combining a low mass strata with a modest thickness of a very conductive material. Properly designed they heat up and cool down quickly. The high and low mass systems each have their place, but the differences are worth learning about for anyone contemplating or living in a radiantly heated home.

For clarity, hydronic radiant panels used for hydronic heating transfers heat predominantly by radiation once the heat gets to the surface of the panel. Due to where it is used, the proportion of heat provided by a convective loop in a room is different for floor, wall and ceiling applications. All rooms are individual circumstances, but radiant floor heating panels may be 58% radiant and 42% convective, radiant wall panel wall may be 75% Radiant and 25% Convective while ceilings may be may 92% radiant and 8% convective.

While the effects of placement of hydronic radiant panel are interesting, more important for this article is how fast a system responds to heating up and cooling down which is related to the panel’s thermal inertia. In general low mass systems respond faster (heat up and cool down) faster provided they are conductive enough to move the needed amount of energy to the surface of the panel and then to radiate and heat the space. This is also termed the thermal inertia of the hydronic radiant panels or radiant board.

In the context of hydronic radiant floor heating systems, thermal inertia can be described as the radiant panel system’s ability to store and slowly release heat. It is the resistance of the panel structure or the materials within it, such as concrete, wood aluminum and a variety of floor coverings to temperature changes. High mass radiant panel systems as exemplified by concrete slabs heat up slowly and cool down slowly. To affect changes in the surface temperature of such a system requires either heating up the whole mass of concrete to raise its temperature or waiting while the whole mass cools down. In a low mass hydronic radiant panel, when properly designed, will respond much faster both to heat up and cool down. Both types of systems have implications for control and application.

In my early experience as a contractor there really were no “low mass, low thermal inertia” systems on the market. Hence I had a lot of experience with high mass, high thermal inertia systems. Later as part of this company, Warm Brothers Inc. We developed and patented a low mass, non structural radiant board called Thermalboard which is part of the growing portfolio of radiant boards, that our company now makes and sells. So, I have a lot of experience with both high and low mass radiant systems and hope my experiences will be helpful.

Radiant Heat Panels To Meet Most Radiant Heating Applications

Our radiant panels deliver efficient heating across multiple applications. We even have Low Mass radiant panals with EPS bonded to the bottom of panel for use over uninsulated concrete slabs. Visit www.wbiwarm.com to see these products. One of my early projects was installing radiant floor heating in a two story building housing a dance studio and office on the ground floor and an office an apartment on the apartmentn the second floor.

Both floors can be described as high mass high thermal inertia systems. The first floor was a slab on grade. They were installed as shown below. The first floor installed with foam steel tubing and cement as shown. In addition there was a floating floor above the slab mounted on 2”x2”x2” foam cubes. This allowed the floor to flex to help prevent injuries of jumping up and down on hard floors. It worked by the concrete radiating heat to the suspended plywood floor which in turn radiated it to the whole room. Since the studios were not used 24 hours a day there was initially, a desire to put a significant set-back when it was not used.

The disadvantages of a high mass system such as this is that it took about four hours to heat back up due to the amount of energy it took to charge the system back. And if the schedule of use changed without it having been anticipated, lightly clad dancers arrived and were cold. The second floor had somewhat less mass with tubing stapled to the subfloor and covered by 1-1/2” of six sack pea gravel mix of cement. It required a second bottom plate and had a similar recovery time profile. Later thermostats that had a learning “adaptive recovery” feature got better at timing setbacks. However, with time the dance studio adopted a “Set and Forget” approach where they did not use set-backs. This was not because it could not be set up with the right control to do setbacks but because the set-back schedule was not easily predicted.

The time lag and thermal fly wheel aspects of slabs on grade make them easiest to control and use in climates with modest temperature swings, basements where temperature swings are moderated by stable ground temperatures, houses with overhangs that minimize solar gain, garages with few windows and in climates where with deliberate solar designs, the thermal mass of a slab can help store and redistribute solar gain. New technology has now made controlling slab-based hydronic radiant panels more reliable and efficient. And our newest panel, InsulHeat™ for use under slabs, has made installing a hydronic slab cost effective. . Here is a link to previous blog on the product: https://wbiwarm.com/blog/hydronic-radiant-floor-heating-in-concrete-slab/

Later Warm Brothers inc. patented Thermalboard™ a low mass, low thermal inertia product which has since been followed by Ecowarm® Radiantboard™ and many others. These systems have many advantages. Simply put they can quickly go through the stages of a radiant panel where it absorbs heat and releases it with out a long period charging a mass getting it to the point where it will release heat.

Over Raised Floor Subfloor

Over Concrete Slab

Optimizing Hydronic Radiant Panels with Outdoor and Indoor Reset Controls

Both types of systems benefit from good controls. An outdoor reset control which adjusts water temperature according to the weather can get the BTU’s being supplied to the heating system a close match tom the heating demand which reduces cycling, prolongs mechanical products and promotes even temperature change. They are very helpful in controlling slabs since once the right curve is found such a control is keeps temperature swings in a high mass system within a range that the fine tuning is then done by the thermostats.

In the low mass board systems we sell, use of outdoor reset controls has a similar benefits and, in particular really helps bring traditional wood flooring systems through temperature changes slowly. The low mass boards we sell have a particular benefit that the quick recovery of the system means many different setbacks and temperatures can be programmed in a day. So if you like the house warm when you wake up, cool while you are gone during the day, warm again for the evening and cool for sleeping a low mass product will easily do that.

Unlike a slab system, if an unexpected guest arrives and you need to quickly heat up the guest suite you can do that. Again thermostats that have adaptive recovery logic will make it work better. Maybe a way to think about it is that its has a bit of AI enabling it to get better at controlling your house. Properly controlled high mass systems can be very stable but are just hard to change quickly. There are climates in the United States that have a heating and cooling load in the same day….desert climates and the central valley of California come to mind. Paying to cool a high mass system that you earlier in the day paid to heat makes absolutely no sense and hence should utilize low mass radiant panel systems.

There are also Indoor Reset Controls which alter the watger temperature based on room temperature. They do not take into account the effects of dramatic weather temperature changes the way an outdoor reset control does. This can be a problem with high mass systems where if the oudoor temperature drops dramatically it will show only later in the room temperature dropping putting a slower responding system behind in catching up.

There are also floor and slab sensing thermostats and some ones that can control both. Usually, the floor sensor is essentially a safety for floor coverings that have a maximum allowed temperature.

ABOUT THE AUTHOR

Hoyt Corbett

Partner, Warm Brothers Inc.

Hoyt has been involved with hydronic heating since the early 1990’s and developed and sold a national brand of radiant floor heating that was acquired by Uponor. Subsequently, Hoyt was Associate Director of the Radiant Panel Association, the industry trade group.

He’s produced extensive technical writing on radiant floor heating, writing several major national hydronic vendor’s radiant heating design and installation manuals as well as founding and publishing The Radiant Flooring Guide.

Call Hoyt at 206-369-1458, 8am to 5pm PST

or

email him at: hoyt.corbett@warmbrothersinc.com

Hydronic radiant floor heating in concrete slab: I wish I had this product when I was a young hydronic radiant contractor.

March 28, 2025/in Blog/by Hoyt Corbett

Our Company, Warm Brothers Inc. has just introduced a much faster and more convenient insulation solution for installing radiant heat in a concrete slab than was available when I was a young installer. I want to introduce this product to you; explain why you do not want to install it in the old way and point out the benefits of using InsulHeat™ instead.

So what is InsulHeat™ Underslab™? Note that it has 4 interlocking edges that make the product easy to install and align.

InsulHeat™ Underslab™ Radiant Floor Heating Panels combine rigid insulation, a vapor barrier and a PEX tubing locking mechanism into a single solution that significantly reduces installation time. The patented “mushroom” shaped nubs lock PEX tubing in place without staples or zip ties. It is design for use under concrete slabs and provides for the placement of PEX hydronic tubing held by the nubs in the foam grid. It features

Four-sided interlocking connectors on every panel
Durable HIPS film acts as a vapor barrier and adds composite strength
Inter-connected channels ensure even heat distribution
Mushroom nubs securely lock tubing
No need for labor intensive concrete “dobies” to support steel
Easier installation and higher compression than blueboard

Get Factory Direct Project Quote Including Freight

In the late 1980’s and 1990’s ….I was a hydronic contractor in the Puget Sound area of Washington State. We installed hundreds of thousands of square feet in concrete slabs in the “old way” that was common at the time. But there is now a much better “new way”. Let me explain how much more work it was to do it the “old way”:

In those days to install hydronic radiant heat in a slab, we would cut to fit and put down 2” thick 4’x 8’ pieces of EPS Foam, adding a vapor barrier. Then the next step was to put down 6” x 6” 8 guage steel mats and then wire them together. Then we raised the mesh up on small cement blocks called “dobies” or up on wire “chairs”. This required us to then bend way over to get our hands around the steel to attach the dobies and then later the tubing ties to the steel every foot or two. We used zip ties, the long end of which often needed to be trimmed off or use bailing wire loops with a twist tool which was a lot of work. And walking on the mesh without displacing the Dobies or chairs was often a challenge. Later if Dobies had not been used, as the concrete pour progressed, the mesh, with the tubing, had to be pulled up into the middle of the slab. This way of installing hydronic radiant heat in a slab worked but was very slow. When I was a contractor, the radiant jobs were spread around Puget Sound, sometimes even on islands. The joke among the crew was we were always either going around water or on the water in a ferry traveling to or from a job. The jobs all involved a lot of travel time, and travel time was expensive. So, coming back another day could threaten profitability. Havin products that are efficient of time is and easy to estimate installation time is very important for all contractors. With the new product InsulHeat™ Underslab™ from Warm Brothers Inc. we are offering a newer labor-saving way to install these systems. If I had had this product when I was a contractor, I would have greatly saved installation time, travel time, money and been more profitable. Below is a graphic of the “old way” we installed hydronic radiant heating in a slab:

THE OLD WAY INVOLVED THE FOLLOWING TIME-CONSUMING DETAILS

THE NEW AND BETTER WAY- INSULHEAT™ UNDERRSLAB™…JUST WALK THE TUBING IN:

This product has numerous advantages…. Speed of Install: the tubing is simply and quickly walked into the grid saving hours of back bending labor. Thus, increasing estimating certainty and improving profits. The easily handled 2’ x 4’ boards have interlocking edges that keep the boards together. There is great freedom for on-site design for experienced contractors. The tubing may be placed in multiple patterns between the nubs. The higher Nubs allow the board to be easily walked on after the tubing is is installed. Mats of 6” x 6” steel wire may be supported on the nibs and lifted as cement is poured. Since the deeper pockets are below the tubing and wire it, is possible for the installers to easily reach down with their hands and pull the mesh up to the middle of the slab as shown below.

The panels have 4 interlocking edges for stability that keep the panels in place, deep pockets to encase the PEX pipe in cement and a vapor barrier layer that also add strength.

This product is ideal for heating barns, garages, new construction slab on grade, new basements and may be used in snow melting.

The product can be used on 6”, 9” and 12” centers. Experienced installers will discover it gives them a great deal of design freedom. Below is an example 12’ x 12’ room laid out on 9” centers. Experienced contractors can often self-design a system using this product. Less experienced users can contact us and use our design service.

Less experienced users can contact us and use our design service.

INSULHEAT DATA SHEET SHOWN BELOW IS AVAILABLE AT : https://wbiwarm.com/wp-content/uploads/2025/03/Product-data-sheet-v1.pdf

ABOUT THE AUTHOR

Hoyt Corbett

Partner, Warm Brothers Inc.

Hoyt has been involved with hydronic heating since the early 1990’s and developed and sold a national brand of radiant floor heating that was acquired by Uponor. Subsequently, Hoyt was Associate Director of the Radiant Panel Association, the industry trade group.

He’s produced extensive technical writing on radiant floor heating, writing several major national hydronic vendor’s radiant heating design and installation manuals as well as founding and publishing The Radiant Flooring Guide.

Call Hoyt at 206-369-1458, 8am to 5pm PST

or

email him at: hoyt.corbett@warmbrothersinc.com

Understanding the Comfort and Efficiency of Radiant Floor Heating

November 14, 2024/in Blog/by Sasha Jeter

How does thermal heat affect your level of comfort?

To fully understand the advantages of radiant panel heating, it’s necessary to understand “thermal comfort”. Although most people know when they’re comfortable, few of them know why. “Comfort professionals” need to understand what factors affect thermal comfort and how to create an interior environment that ensures it exists.

Ecowarm Radiant Floor Heating Provides Warm Thermal Comfort Floors and cookies are best when warm. Infrared photography shows why radiant floor heating is the most comfortable and efficient heat available.

Many people think that just because the room temperature is in the range of 70F, they should be comfortable. Providing true thermal comfort, however, involves more than simply maintaining inside temperature within a certain range.

Comfort is established and maintained only as long as our bodies release the heat generated by metabolism at the same rate it’s produced. When truly comfortable, we should be totally unaware of how or where our bodies are losing heat. Radiant heat transfer plays a big part in providing – or denying – thermal comfort.

To appreciate the intricacies of maintaining thermal comfort, it’s important to understand how our bodies release heat. Under light activity conditions, such as working at a desk, an adult generates about 350 to 400 Btus per hour of heat by metabolism. That’s roughly equivalent to the heat given off by a 100 watt light bulb.

“When truly comfortable, we should be totally unaware of how or where our bodies are losing heat. Radiant heat transfer plays a big part in providing – or denying – thermal comfort.”

The Four Natural Heat Processes

Four natural processes are involved in releasing heat from the body:

Evaporation of moisture from the skin
Heat transferred to the air around the body by convection
Heat conducted to objects the body is in contact with
Radiant heat transfer between the body and surrounding objects

The combined effect of all four processes determines if we release heat at the same rate it’s generated, and hence whether or not we’re comfortable.

Evaporation

Evaporation of moisture from the skin is responsible for about 25% of the heat output of our body during light activity within typical interior spaces. As the humidity of the air around us increases, evaporative heat loss becomes less effective. Moisture accumulates on our skin faster than it can evaporate. You know the feeling-and the resulting loss of thermal comfort.

By contrast, evaporative cooling is very effective (and therefore very noticeable) before a person towels off after a swim, even when the temperature of the air surrounding them would otherwise be considered comfortable.

Convection

Heat flows from our skin and clothing to the surrounding air whenever the air is at a lower temperature. This is an example of convection heat transfer.

As the air in contact with our skin and clothing absorbs heat it gently rises, cooler air flows in to replace it and continues the process. Under normal interior conditions, while wearing light clothing, convection removes about 30% of the heat our bodies generate. Its effectiveness depends on both the temperature difference between our external surfaces and the air around us, as well as the speed the air flows past us.

Increasing either increases convective heat loss. For example, we experience “wind chill” whenever air at a temperature lower than our exterior surfaces flows past us. As the speed of the air increases, we feel a definite increase in its cooling effect, even though its temperature hasn’t dropped.

Although wind chill is usually thought of as an outdoor phenomena, it can also occur inside. The word “draft” is used to describe this (usually undesirable) effect during the heating season. To maintain comfort, heating systems in floors must avoid creating noticeable drafts.

“Although wind chill is usually thought of as an outdoor phenomena, it can also occur inside. The word “draft” is used to describe this (usually undesirable) effect during the heating season.”

Conduction

Heat loss by conduction occurs whenever part of our body touches a colder object. If you stand barefoot on a cool basement floor, your feet quickly feel the result of conduction heat loss. The warmed seat of a chair after someone has been sitting in it for a while is also the result of conduction heat loss.

Radiation

Radiant heat transfer from our skin and clothing to objects around us plays a big role in determining thermal comfort. Whenever we’re in the proximity of objects cooler than our exterior surfaces, we radiate heat to them.

Under normal interior conditions with light clothing, almost half of our body’s total heat output is released by radiation. This is what creates the chill we feel while standing near a cool window surface, even though the air around us may be 70F or more. Another way to feel radiant heat loss is to walk out from under an overhang on a clear night. There is an instant sense of the increased cooling effect as your body comes into view of the cold upper atmosphere that was previously shielded by the overhang. The surrounding air temperature didn’t change, but the increased radiational cooling makes it feel that way.

“…almost half of our body’s total heat output is released by radiation. This is what creates the “chill” we feel while standing near a cool window surface, even though the air around us may be 70F or more.”

How do our bodies regulate heat loss?

Our bodies automatically adjust all these processes to regulate heat loss. When one method of heat loss is limited, the body attempts to increase its other heat loss mechanisms.

For example, when high humidity inhibits evaporative heat loss, our skin temperature rises in order to boost both convection and radiation heat loss. In such situations our instincts often tell us to increase convection by fanning our face, standing where there’s a breeze, and so forth. But there are limits to how far our bodies can adjust one or more of these mechanisms to compensate for others.

That’s where a building’s “comfort system” comes in. Ideally, it works in combination with our body’s own heat loss mechanisms, keeping them within a fairly narrow range so they can “fine-tune” body heat output and thus maintain comfort.

“…thermal comfort is achieved when we are totally unaware of how or where our bodies are losing heat.

How to achieve maximum thermal comfort

We’ve probably all experienced most of the uncomfortable situations described above, but few of us have paused to give them much thought. Now that you have a basic understanding of how these natural processes work, you’ll become more discerning of your thermal surroundings and the degree of comfort they offer. Remember, thermal comfort is achieved when we are totally unaware of how or where our bodies are losing heat.

Radiant Ceiling Vs Radiant Floor Heating

November 14, 2024/in Blog/by Sasha Jeter

Tom Tesmar is a legendary pioneer in the introduction of Euro style modern radiant heat to North America. We think Tom says it best.

Thermodynamics is not just a good idea….it’s the law. The output of a radiant floor is limited in two ways. First, the maximum surface temperature of a radiant floor is limited to around 87F (about 45 Btu per square foot). If the floor is operated above this temperature, the occupants are likely to complain of uncomfortably hot and sweaty feet.

The Benefits of Radiant Heat in your Ceiling vs the Floor

Secondly, radiant floors are limited by the amount of energy that can penetrate highly resistant floor coverings, such as certain carpeted and wood floors. Often, these materials limit the actual output to less than 20 Btu per square foot. Unfortunately, these beautiful and thermally resistant floor coverings are often used in the more elegant rooms, with large windows and high heating loads. Radiant floor designers often must stretch to meet the load such rooms. Also, floor coverings are likely to change significantly over the life of the building, leading to the comment “It worked until the owners placed a thick Persian rug over the wood floor”.

Radiant ceilings can easily operate at surface temperatures up to 100 F, delivering in excess of 55 Btu per square foot. Since ceilings are typically constructed of gypsum based sheet rock, they offer very little resistance to thermal transfer. Unless designers regress to the 1960’s, and resume putting shag carpeting on the ceilings, it’s likely the output of the ceiling won’t change during the life of the home.

“There seems to be some ingrained misunderstandings of the concepts. Someone will say that “heat rises, therefore you’ll have a hot head and cold feet”. Not true.”

In any discussion of radiant ceilings and comfort, there seems to be some ingrained misunderstandings of the concepts. Someone will say that “heat rises, therefore you’ll have a hot head and cold feet”. Not true.

Addressing the “Heat Rises” Myth

Heat doesn’t rise. Hot air rises. In radiant systems objects of mass are heated without heating the air. In fact, there is typically more hot air rising with a radiant floor than with a radiant ceiling. This is because air molecules that come into contact with the radiant ceiling already occupy the highest strata. In radiant floors, the cooler molecules sink and come into contact with the warm floor surface and rise as their density changes with heat, driving the convective forces that cause stratification.

Under normal conditions neither radiant floors or radiant ceilings heat the air to an uncomfortable level like in forced air systems, however.

“There are no cold floors in radiant ceiling projects.”

Another myth about radiant floors and ceilings involves the surface temperatures that are achieved. Just as the overhead rays of the sun are absorbed by the beach sand, radiant ceilings warm the floor. There are no cold floors in radiant ceiling projects. You can put a piece of Tahiti in your living room with radiant ceilings. Unless you believe tropical island comfort requires the flow of underground lava.

I also hear radiant ceilings criticized for what is termed “shadowing affects”. This is the belief that legs under tables or desks are shielded from the radiant heat and are, therefore, cold. Radiant ceilings, like floors both radiate and re-radiate. The invisible heat rays emit from the heated surface to other colder unheated surfaces. The total affect of all of this bouncing of energy is very even heat distribution.

If a person is seated at a table near an outside wall, there could be some shadowing from above with a radiant ceiling, just as there might be shadowing from below with a radiant floor when seated on a sofa near the outside wall. In most situations, shadowing for radiant ceilings or floors is negligible. More significant, however is the possibility that objects placed on the radiant floor will impede the flow of energy. Area rugs, and some furnishings such as certain sofas and beds can reduce the usable floor area, increasing the Btu load per square foot, and, perhaps, exceeding the system capability. Radiant ceilings are not subject to these types of problems.

Cost Benefits of Radiant Heat in Ceilings

Radiant ceilings accelerate fast, when needed, to meet a big change in heating load. They dissipate energy fast as well. The responsiveness of radiant ceilings makes them excellent for modern controls, placing energy where it is needed when it is needed, and achieving superior comfort and efficiency. Some high mass radiant floors are sluggish in that they take a long time to accelerate to meet the load.

In modern heating systems, too much emphasis has been placed on energy efficiency of the heat plant while wasting energy on poor distribution. This is like putting a Viper engine in a Yugo. Far more heat energy can be salvaged by not wasting it in poorly controlled buildings, than can be achieved by squeezing another Btu per hour out of a heat plant. There are some pretty interesting solutions to heat distribution problems by using radiant floors in conjunction with radiant ceilings.

“Without a doubt, radiant ceilings cost far less than radiant floors.”

In this way the floors are not required to meet the entire load, yet are conditioned to provide comfortable surface temperatures. The ceilings are heated, where necessary, to take on the severe conditions and give everyone involved the peace of mind that the system will keep up with the heat loss under severe conditions. Without a doubt, radiant ceilings cost far less than radiant floors. In most are heated, where necessary, to take on the severe conditions and give everyone involved the peace of mind that the system will keep up with the heat loss under severe conditions.

Without a doubt, radiant ceilings cost far less than radiant floors. In most cases they cost less than half of a radiant floor. Lower cost means more opportunity. They take less effort to design and install. Radiant ceilings are perfect for retrofit situations. It is very inexpensive and easy to lower a ceiling to accommodate the radiant ceiling, but difficult to raise a floor.

Radiant ceilings are not optimal over a concrete slab placed on the grade of the earth. Radiant floors are best for these situations. I also prefer radiant floors in rooms with smooth surface floors, such as bathrooms, where occupants are often barefoot. It is a real nice touch. But when the going gets tough, the heat losses are high and the floor coverings are plush, radiant ceilings cannot be beat.”

Tile Over Radiant Heating Boards

November 14, 2024/in Blog/by Sasha Jeter

Cost Effective Installation of Tile Over Radiant Floor Heating Boards

This radiant floor heating article is designed to communicate a quality and cost effective method of installing ceramic tile over radiant floor heating board systems. The system shown below is straight forward and avoids using unnecessarily expensive and complex products.

Overview of Materials:

All materials expand and contract at different rates and with tile it is particularly important to accommodate this in a quality installation over radiant heating boards. Radiant floors typically go through a range of floor temperatures depending on the amount of heat loss occurring at the time.

In moderate weather the floor temperature may only be a few degrees hotter than the room temperature but in extreme heat loss conditions it could under certain circumstances be as much as 15°F hotter than the room temperature. The co-efficient of thermal expansion of the radiant board substrata and ceramic tile are not the same. Properly installed tile is very durable but will be prone to cracking if provision is not made to account for the differing expansion of these layers of materials.

By utilizing a flexible crack isolation membrane this challenge can be cost effectively solved and also provide, with proper installation and material choice, protection from moisture getting into the substrata. Since tile is so frequently installed in locations that are prone to moisture such as bathrooms and kitchens this moisture protection is important.

Suggested Installation Method for Tile over Radiant Floor Heating

The system described above is the cost effective system that our company recommends for our Ecowarm Radiant Board. But it is generic enough that, with small common sense changes should be applicable to most infloor radiant board systems.

In the drawing the radiant board is attached to the subfloor using, preferably, a low VOV green construction adhesive glue on the bottom along with screws or cross staples from a sheathing stapler at the eight attachment points. Cross stapling means putting 2 staples at opposing 45 degree angles close to each other. Cross stapling along with the bottom side glue makes for a very secure and squeak resistant installation of the board. The next step is installing cementitious backer board over the radiant board. It may be ¼” .3/8” or ½” depending on the needs of matching other floor heights.

How to have a record of where the tubing is:

Before installing the backer board a thick sheet of clear plastic should be cut to size of the room or area to be installed with the backer board. Using a permanent marker make a template of where the tubing runs are. The plastic template can be unrolled and used to locate where to snap lines that will locate the tubing to avoid screwing through. Taking photographs of the tubing installation is a good idea also. The backerboard may be installed to the radiant board using modified thin set and screwed to the radiant board.

The hydronic tubing should be under an air pressure test during the installation so that if a puncture occurred it would be found. To date we have not found a modified thin set that is incompatible with the PEX pipe used in the radiant board but it is always good to check with the PEX manufacturer as well. There are other PEX pipe compatible adhesives such as Bostik Greenforce that can be used to adhere backerboard to our radiant board but are more expensive than thin set. Remember all glues take longer to set on aluminum since only one of the two surfaces is absorbent. Once the backerboard is attached to the radiant board, an anti-fracture membrane should be installed over it.

We recommend products from the Noble Corporation http://noblecompany.com since they were early supporters of the radiant floor heating industry and trade groups called and have very radiant savvy tech support people. They make a range of appropriate products but the one we recommend is called Noble Seal TS http://noblecompany.com/products/nobleseal-ts which performs as a crack isolation or antifracture membrane and when properly installed adds water proofing of the substrata. Properly installed and rated in TCNA approved tests as High Performance, it will accommodate up to 1/8” differences in the expansion and contraction of the layers thus preventing cracking of the tile.

Photo courtesy of The Noble Company

The anti-fracture membrane is made from an extruded CPE sheet layer pf polyester fiber bonded to either side. TS may be installed on the cementitious backboard in two ways. The first way is with modified thin set mortar which requires a cure time before the installation of the tile, or in the case of Noble Seal TS there is an adhesive called Nobel Bond EXT that can be used that has enough tack that tile may be installed using modified thin set on it, without the additional cure time. The membrane may be made waterproof by lapping it 2”and using a waterproof sealant such as NobleSealant 150 to bond the overlap.

There are other brands with anti-fracture membranes and a family of related products where the installation would be similar. Lastly, tile is usually thin set to the anti-fracture membrane and after an appropriate drying period grout is applied.

5 Ways Radiant Heat Is Better In The Ceiling

5 Ways Radiant Ceiling Heat is Better

November 14, 2024/in Blog/by Sasha Jeter

The Upside of Radiant Heat in Floors

Ask almost anyone in the heating trade about radiant panel heating and they’ll probably start describing tubing embedded in floors. Radiant floor heating is by far the biggest part of the radiant panel market. It’s an excellent approach in many projects ranging from residential all the way up to heavy industrial applications. However, it’s not necessarily the ideal solution in the coming generation of low-energy-use houses.

“Radiant floor heating is by far the biggest part of the radiant panel market.”

When viewed only from the standpoint of heat source performance, the low operating temperature of a bare concrete slab with closely spaced tubing (6-in. to 9-in. spacing) is very beneficial. A well-insulated house on a design day may only require supply water temperatures in the range of 85° F to 90° to maintain the interior space at 70°. Condensing boilers, solar collectors and hydronic heat pumps all love to operate at these low temperatures and show their gratitude by operating near the upper end of their performance range.

Radiant Heating Installed In Ceilings And Floors

The Benefits of Radiant Heat in Ceilings

That’s the good news. The downside is two-fold: First, the average floor surface temperature required for a heated floor in a well-insulated house is only a few degrees above the room temperature. You can estimate this average floor surface temperature using Formula 1.

“The downside is two-fold: First, the average floor surface temperature required of a heated floor in a well-insulated house is only a few degrees above the room temperature.”

Formula 1

Where:

TS(ave) = average floor surface temperature (°F)

TR = room air temperature (°F)

q = upward heat flux from floor (Btu/hr./ft2)

For example, imagine a house with 2,000 sq. ft. of heated floor area and a modest design heat loss of 30,000 Btu/hr. The required upward heat flux under design load conditions is: (see above)

Assuming the room air temperature was to be maintained at 70°, the average floor surface temperature would be: (see above)

This temperature is at or slightly below normal bare skin temperature. In such a case, heat would be conducting from the foot or hand to the flow, as shown by the infrared image in Figure 1. During most of the heating season, the floor surface temperature would be even lower, perhaps around 74° when the outdoor temperature is 35°.

“True, the floor is still warmer than it would be with convective-type heating. But it may not be delivering the “barefoot friendly” effect so widely advertised as a benefit of radiant floor heating.”

True, the floor is still warmer than it would be with convective-type heating. But it may not be delivering the “barefoot friendly” effect so widely advertised as a benefit of radiant floor heating. The fact that the room is still maintained at 70° is unlikely to placate the unmet customer expectations of warm-to-the-touch floors.

The other drawback is thermal response. Low-energy-use houses are especially susceptible to rapid temperature changes from internal gains. In many new homes, this is further exacerbated by above-average passive solar heat gains.

These characteristics don’t bode well for high-mass heat emitters, such as heated concrete slabs. Spaces will quickly overheat when the sun comes out and much of the solar gain will be lost through the ventilation necessary to keep the house from turning into a sauna.

Low-energy-use houses need heat emitter systems capable of rapidly changing their rate of heat delivery. Think Jet Ski rather than oil tanker. One good candidate is a low-mass radiant ceiling panel.

“Radiant heated ceilings deliver more than 90% of their heat output as thermal radiation. They “shine” thermal radiation down into the room much as a light fixture shines visible light downward.”

5 Ways Radiant Ceiling Heat is Better

Heated ceilings deliver more than 90% of their heat output as thermal radiation. They “shine” thermal radiation down into the room much as a light fixture shines visible light downward. They offer several benefits:

Radiant heated ceilings have low thermal mass.

Low-mass radiant ceilings can quickly warm up following a cold start. They are ideal in rooms where quick recovery from setback conditions is desirable. Low mass also means they can quickly suspend heat output when necessary. This helps limit overheating when significant solar heat gain occurs.

Radiant heated ceilings higher heat output.

Because occupants are not in contact with them, radiant heated ceilings can be operated at higher surface temperatures than radiant floors. This allows greater heat output per sq. ft. of ceiling. For example, a ceiling operating at an average surface temperature of 102° releases approximately 55 Btu/hr./ft2 into a room maintained at 68°. This is almost 60% more heat output than a radiant floor with a mean surface temperature limit of 85°.

Not affected by changing floor coverings.

It’s probably safe to say the days of shag-carpeted ceilings are over. Ceilings are the least likely surface of a room ever to be covered, especially by anything with high thermal resistance. Thus, the output of a heated ceiling is very unlikely to be compromised by future changes, such as surface coverings or furniture placement. Similarly, the heated floor under vinyl plank works exceptionally well together, as luxury vinyl has low thermal resistance, allowing efficient heat transfer without compromising comfort or performance.

Radiant heated ceilings warm objects in the room.

The energy emitted from a radiant heated ceiling is absorbed by the surfaces in the room below. This includes unobstructed floor area as well as the surfaces of objects in the room. The upward-facing surfaces tend to absorb the majority of the radiant energy; the top of beds, tables and furniture are slightly warmer than the room air temperature. The surface temperature of floors below an active radiant ceiling will be slightly warmer than they would be if the room were heated by convection.

Radiant heated ceilings are easy to retrofit.

Radiant ceilings are usually easier to retrofit into existing rooms than are radiant floors. They add very little weight to the structure and require minimal loss of headroom. Likewise, radiant floor systems using Ecowarm RadiantBoard are also ideal for remodels and retrofits, thanks to their lightweight, low-profile design and quick installation, making it easy to upgrade heating systems.

Interested in a Free Quote?

Our panels offer the best balance of high-performance, cost, and environmental responsibility in the radiant floor panel heating market. Give us a call at 866-341-1854 or submit a request for a free quote delivered factory direct to your jobsite.

Tile Over Radiant Heating Boards

September 30, 2024/in Blog/by Sasha Jeter

Cost Effective Installation of Tile Over Radiant Floor Heating Boards

This radiant floor heating article is designed to communicate a quality and cost effective method of installing ceramic tile over radiant floor heating board systems. The system shown below is straight forward and avoids using unnecessarily expensive and complex products.

Overview of Materials:

All materials expand and contract at different rates and with tile it is particularly important to accommodate this in a quality installation over radiant heating boards. Radiant floors typically go through a range of floor temperatures depending on the amount of heat loss occurring at the time.

In moderate weather the floor temperature may only be a few degrees hotter than the room temperature but in extreme heat loss conditions it could under certain circumstances be as much as 15°F hotter than the room temperature. The co-efficient of thermal expansion of the radiant board substrata and ceramic tile are not the same. Properly installed tile is very durable but will be prone to cracking if provision is not made to account for the differing expansion of these layers of materials.

By utilizing a flexible crack isolation membrane this challenge can be cost effectively solved and also provide, with proper installation and material choice, protection from moisture getting into the substrata. Since tile is so frequently installed in locations that are prone to moisture such as bathrooms and kitchens this moisture protection is important.

Suggested Installation Method for Tile over Radiant Floor Heating

The system described above is the cost effective system that our company recommends for our Ecowarm Radiant Board. But it is generic enough that, with small common sense changes should be applicable to most infloor radiant board systems.

In the drawing the radiant board is attached to the subfloor using, preferably, a low VOV green construction adhesive glue on the bottom along with screws or cross staples from a sheathing stapler at the eight attachment points. Cross stapling means putting 2 staples at opposing 45 degree angles close to each other. Cross stapling along with the bottom side glue makes for a very secure and squeak resistant installation of the board. The next step is installing cementitious backer board over the radiant board. It may be ¼” .3/8” or ½” depending on the needs of matching other floor heights.

How to have a record of where the tubing is:

Before installing the backer board a thick sheet of clear plastic should be cut to size of the room or area to be installed with the backer board. Using a permanent marker make a template of where the tubing runs are. The plastic template can be unrolled and used to locate where to snap lines that will locate the tubing to avoid screwing through. Taking photographs of the tubing installation is a good idea also. The backerboard may be installed to the radiant board using modified thin set and screwed to the radiant board.

The hydronic tubing should be under an air pressure test during the installation so that if a puncture occurred it would be found. To date we have not found a modified thin set that is incompatible with the PEX pipe used in the radiant board but it is always good to check with the PEX manufacturer as well. There are other PEX pipe compatible adhesives such as Bostik Greenforce that can be used to adhere backerboard to our radiant board but are more expensive than thin set. Remember all glues take longer to set on aluminum since only one of the two surfaces is absorbent. Once the backerboard is attached to the radiant board, an anti-fracture membrane should be installed over it.

We recommend products from the Noble Corporation since they were early supporters of the radiant floor heating industry and trade groups called and have very radiant savvy tech support people. They make a range of appropriate products but the one we recommend is called Noble Seal TS which performs as a crack isolation or antifracture membrane and when properly installed adds water proofing of the substrata. Properly installed and rated in TCNA approved tests as High Performance, it will accommodate up to 1/8” differences in the expansion and contraction of the layers thus preventing cracking of the tile.

Photo courtesy of The Noble Company

The anti-fracture membrane is made from an extruded CPE sheet layer pf polyester fiber bonded to either side. TS may be installed on the cementitious backboard in two ways. The first way is with modified thin set mortar which requires a cure time before the installation of the tile, or in the case of Noble Seal TS there is an adhesive called Nobel Bond EXT that can be used that has enough tack that tile may be installed using modified thin set on it, without the additional cure time. The membrane may be made waterproof by lapping it 2”and using a waterproof sealant such as NobleSealant 150 to bond the overlap.

There are other brands with anti-fracture membranes and a family of related products where the installation would be similar. Lastly, tile is usually thin set to the anti-fracture membrane and after an appropriate drying period grout is applied.

Designing Radiant Floor Heating That Is The Best Combination of High Performance, Environmental Responsiblity And Cost

September 30, 2024/in Blog/by Sasha Jeter

I grew up in a house with an addition with radiant floor heating. My mother was a Frank Lloyd Wright fan and so the new wing on our house had radiant floor heating with tubing in concrete covered with a thin cork floor. Frank Lloyd Wright was an early proponent of radiant floor heating. I remember it was always warm and inviting in the big playroom with radiant heat where we kids always played. Later as a professor at the University of New Mexico in the early 1980s, I met a Norwegian who was promoting and educating people about radiant floor heating. Again I was amazed at how comfortable it was. This time I also wanted to understand the thermodynamics of how it worked and all the ways it could be installed. Thus began my now 36 year involvement with radiant floor heating.

Why Modern Architects & Builders Choose Radiant Floor Heating

September 30, 2024/in Blog/by Sasha Jeter

Article written by Morgan Muir

I am writing this article so that architects and builders can learn more about radiant floor heating, and to provide a tool for introducing clients to radiant floor heating, and why they should choose Ecowarm RadiantBoard.