Tile Over Radiant Heating Boards

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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.

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

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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.

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Why Modern Architects & Builders Choose Radiant Floor Heating

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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.

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Understanding the Comfort and Efficiency of Radiant Floor Heating

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Article written by Morgan Muir

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.

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Radiant Ceiling VS Radiant Floor Heating

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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.”