May Feature – Schluter Systems Floor Heating

Ceramic and stone tiles are ideal surface coverings because they are durable, hygienic, and easy to maintain. However, a common objection to tile as a floor covering is that it can be cold underfoot. This is especially true in colder climates during the winter months. There are various floor-warming systems available that can help our industry overcome this challenge and increase tile consumption, to the benefit of manufacturers, distributors, dealers, installers, and home owners alike. In fact, floor-warming is seen as an affordable luxury to many home owners. It’s a perfect marriage, as tile is the best covering for floor-warming systems, given its ability to effectively transfer heat.

Systems based on hydronic tubing keep floors warm, but are typically used as the primary heating source for the home. These systems can increase comfort and reduce energy costs, but if an owner is only interested in keeping his or her feet warm in the bathroom while getting ready for work in the morning, an electric floor-warming system is a more practical choice. And today’s electric floor-warming systems have made it so that warm floors are no longer a luxury for the few, but an attainable option for every home with tiled floors.

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A thin sheet of plywood was used as a placeholder while the 12″ x 24″ marble field tiles were installed. The heating cables were first protected by a layer of unmodified thin-set mortar.

The basics

The heat source for most electric floor-warming systems is a cable comprised of a heating element (wire) that is protected by sheathing and surrounded by a ground element and a polymer jacket. The resistance of the wire causes electrical energy to be converted to heat energy. This heat energy warms the floor covering above.

Heating cable assemblies are produced in different configurations. In the simplest form, the cable is purchased on a spool and placed on the floor at the manufacturer-specified spacing. It is held in place by clips or tracks fastened to the subfloor. Cables may also be purchased mounted on a plastic mesh or within a sheet at a consistent spacing and attached to the floor. These products are available in standard and custom sizes. For loose cables and those mounted on mesh, best practice is to embed the heating cables in a self-leveling underlayment. Once the SLU sets, tile installation may begin.

Today’s innovations

The latest innovation in electric floor-warming is a new form of uncoupling membranes, which feature studs that secure heating cables without the use of clips or fasteners. These systems offer complete flexibility because cables can be placed wherever heat is desired, without creating height differences in the floor. Furthermore, self-leveling compounds are not required to encapsulate the cables. Tile can be installed immediately after the cable is placed, thereby significantly reducing installation time.

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Electric heating cables were run in all areas that would have foot traffic, taking care to maintain proper and consistent spacing of the cables throughout.

In addition to the floor-warming installation benefits, uncoupling membranes provide other functions to protect the assembly. They provide uncoupling through their geometric configuration, which allows the substrate and tile to move independently, thus mitigating movement stresses and preventing the major cause of cracking and delaminating of the surface covering. Many uncoupling membranes also function as waterproofing membranes to protect the substrate from moisture penetration. This is particularly important in bathrooms and kitchens, which are common areas for tile and floor warming, and can often be exposed to water. The free space on the underside of the membranes provides a route for excess moisture and vapor to escape from the substrate that could otherwise cause damage to the tile covering above. Finally, loads are transferred from the tile through column-like mortar structures formed in the membranes to the substrate. Thus, the advantages of uncoupling are achieved without sacrificing support for the tile covering.

Project feature

We spoke to NTCA member Mike Corona of Corona Marble & Tile Ltd., in Woodbine, Md., regarding an excellent example of a well-executed floor-warming tile installation. Case Builders of Lutherville, Md., was performing three bathroom renovations and adding a 3,500 sq. ft. addition to a home in Hanover, Pa. During the planning process, the homeowner commented that she was always frustrated with the floor in the master bathroom being cold. Corona suggested using the Schluter®-DITRA-HEAT system to provide floor warming and ensure a lasting tile assembly. He already had extensive experience with the system, as it has become his standard choice for floor-warming applications, and enjoys the “all-in-one” nature of the system.

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The shower drain was placed to complement the pattern on the mosaic on the shower floor.

The DITRA-HEAT was installed in all areas of the 125-sq.-ft. bathroom where foot traffic is common. They made use of a 240-volt dedicated circuit that was present in the bathroom and became available when the owner decided to remove the jetted hot tub. Removing large hot tubs during bathroom renovations has become more common and represents a great opportunity to save time and cost when providing power to floor-warming systems.

The sub assembly consisted of joists spaced at 16″ o.c., 3/4″ -thick plywood subfloor, and 1/2″ -thick plywood underlayment to support the stone tile installation. The tile setter prepared the plywood substrate with a self-leveling underlayment prior to installing the DITRA-HEAT in order to provide a flat substrate for the tile installation. Chesapeake Tile & Marble of Owings Mills, Md., supplied the Calacatta Gold 12″ x 24″ marble tile for the floor and New Ravenna mosaics that were used to create two inlays in the tile field. MAPEI® setting materials (self-leveling underlayment, thin-set mortar, and large-and-heavy tile mortar) were used throughout.

Getting started with your installation

In general, installation of floor-warming systems is relatively straightforward. When installation problems arise, there are some common culprits. Keep these tips in mind on your next installation:

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Care was taken to match the height of the mosaic inlay to the height of the marble field tile.

  • DO read and follow all instructions. Period.
  • DO partner with a qualified electrician who can verify that the installation conforms to applicable electrical and building codes. This will help ensure a safe application and avoid conflicts with building code officials.
  • DON’T overestimate the amount of heating cable required. Most cable systems CANNOT be cut to fit; this will change the resistance and could lead to fire. Consider that heating cables cannot be installed under fixtures and must be spaced at approved distances from walls, floor drains, and other heating sources when making your calculations. It is also recommended to plan for a “buffer zone” in the room where floor warming isn’t required (i.e., where it can be placed, but people are not likely to stand). In the event a mistake is made and too long a cable is purchased, you’ll have a place to put the “excess.” Many manufacturers have online tools to help you determine the correct length of cable for your application.
  • DO test the heating cables according to manufacturer’s instructions. This should be done at various times during and after installation (e.g., immediately after removal from packaging, after cable installation, and after tile installation). Testing can help catch a problem early and avoid costly tear out. Manufacturers’ warranties are typically void if the cable is not tested according to their requirements.
  • DO inform other trades that heating cable has been installed and where it is located. Once your work is complete, the last thing you want is to receive a call from the general contractor saying the heating cable isn’t working because the plumber unknowingly damaged it cutting a hole to run a drain pipe.