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Radiant Floor Heating Installation Basics

Radiant floor heating installation over subfloor preparation

Radiant floor heating can be installed on any grade level in a home or business as long as the added weight of the radiant heating system can be supported. Because hydronic systems carry water through the floor and are usually installed in heavy cement, they can add a significant load to the floor. Electric heated systems that use a dry installation method tend to be the lightest and can be used in areas where hydronic systems are too heavy.

Note on Wet and Dry Installations: Wet installations involve laying mats, tubes, or cables into a wet surface, such as concrete, that then hardens. Dry installations, on the other hand, do not require the use of a substrate like concrete.

Over time, radiant heating can change the moisture content and temperature of floor coverings. If the type of floor covering being used was not built to handle these types of changes, it is not recommend that you install it over radiant heating.

Suitable Floor Coverings with Radiant Floor Heating

Radiant floor heating systems work well with ceramic, porcelain
and stone tile

Ceramic, porcelain, and stone tile are all excellent choices for use with radiant heating as they conduct and hold heat well. Laminate floors are another good choice because they are a relatively stable floor but you should always check with the manufacturer and carefully coordinate the installation.

On the other hand, floors that expand and contract considerably from changes in moisture and temperature, like hardwood, for example, require greater caution when installed with radiant floor heating systems. It is crucial that you always first check with the manufacturer's recommendations. It's usually helpful to choose engineered hardwood floors over solid hardwood floors because they are more stable. The same goes for bamboo floors.

Radiant floor heating systems work well with engineered
hardwood flooring where caution should be taken with solid hardwood flooring

When Choosing Solid Hardwood: If you are adamant in choosing a solid hardwood floor, there are some basic rules that you should follow. You should not choose planks that are any wider than 3". Choose very stable woods such as Brazilian Cherry, Tigerwood and Ipe. It is also better to choose hardwood floors that are said to be quarter sawn, rift sawn, straight grain, or vertical grain, as opposed to plain sawn. These hardwoods are more stable in width and will not expand/contract as much as other cuts of hardwood.

Note: Floating floor covering installations are easiest to coordinate with radiant heating systems as they eliminate the need for adhesives, nails, and staples, and allow the floor to expand and contract as a whole.

When using radiant floor heating with carpet, it's best to choose thin carpet with dense padding. Vinyl, linoleum, and cork can also be used but keep in mind that the thicker the floor covering is, the harder heat will have to work to reach the surface. Again, always adhered to all manufacturer recommendations to maintain your warranty and protect your floor covering.

Basic Hydronic and Electric Radiant Heating Installation Methods

Installed Over Subfloor

Illustration of radiant floor heating installed over wood subfloor

There are several different types of both electric and hydronic radiant heating systems that are installed over the subfloor, rather than under. There are pre–manufactured systems such as electric mesh which can often be installed directly under the floor covering as well as electric and hydronic tubing or cable systems that are usually sandwiched between the concrete or wood subfloor and plywood or cement board underlayment. Many of these systems use metal or aluminum sheets to further conduct heat.

Note: If the sub floor is accessible from its underside when installing radiant floor heating, you leave yourself the option of accessing the heating system from the underside of the floor in case of the need for future repairs.

Installed in Wet Concrete Slab

Illustration of radiant floor heating installed in wet concrete

With this wet radiant heating installation method, a radiant mat, tubing, or cable system is imbedded in a concrete foundation slab. Radiant heating installed in a wet concrete slab is also known as the slab on grade installation method though it can be installed several feet below grade as well. Radiant heating installed using the wet concrete slab method is more commonly used during new constructions while the home foundation is being poured and is usually 4" thick, though thickness may vary. A professional installation is recommended when installing radiant heating in a wet concrete slab.

Note on Floor Elevation Considerations: It is important to note that some floor heating systems can elevate a floor by a considerable couple of inches. When this in an issue, you may prefer electric radiant heating systems which can be very thin (often under 1/8" of an inch).

Installed in Wet Concrete Overlay

Illustration of radiant floor heating installed in wet concrete

This radiant heating installation method involves laying hydronic tubing or electric cables or mats into a thin concrete overlay or other hardening material. In most cases, the tubing, cables, or mats are laid first, and then the concrete or other hardening material is poured overtop the radiant heating system. This method is used in both new homes and home renovations and can be anywhere from 3/8" thick to 1–1/4" thick. A professional installation is recommended for any radiant heating system installed in a wet concrete overlay.

Installed Under Subfloor (Between Floor Joists)

Illustratin of radiant floor heating installed under subfloor
betweem floor joists

Hydronic or electric radiant heating is attached to or hanging from the underside of the existing subfloor. This is done by accessing the air space between the floor joists from the bottom of the floor. Installing insulation below the radiant heating is recommended in order to reflect the heat upward towards the surface and into the room above. It is also common to install metal plates beneath the radiant heating or attached to the tubes themselves in order to diffuse the heat further. This dry installation method is used when radiant heating is being installed during a home renovation.

Radiant Systems with Built-In Subfloor

Illustratin of radiant floor heating installed under hardwood
with built-in subflooring

Some radiant heating systems are built to serve as both the subfloor, as well as the radiant heating system itself. These pre–manufactured radiant heating systems are commonly called structural radiant subfloors, though they may fall under many other names. In many cases, they have grooves where the hydronic or electric radiant heating cable or tubing is laid into during installation. While these are often easier to install than wet radiant heating installations, a professional installation is also recommended for radiant heating systems with built in subfloors.

Important Note: Please note that local mandates may require a license to install new sources of heat, especially if a boiler is being used. Check with your local authorities for more details.

If you need more help with your radiant floor heating installation, be sure to use FindAnyFloor's Live Chat Help or visit our Flooring Forums.