All About Installing Wood Floors Over Radiant Heat

By Jeff Hosking, President of Hosking Hardwood Flooring
© 1997-2006, Copyright Hosking Hardwood Flooring. All Rights Reserved.

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With new building and remodeling practices, the demand for using in-floor radiant heat has increased dramatically with in the last 25 years. Radiant heat provides an even warmth with no cold spots within a room and provides a comfort that cannot be matched by any other type of heating system. Over the years, we have installed a lot of wood flooring over different types of radiant heat systems including many for the PBS television series "This Old House". This Old House TV Series Projects

Early in-floor radiant heat systems were temperamental, expensive and only a hand full of heating companies had the experience to install them. Nowadays, radiant heat systems have become a lot more prevalent, affordable and reliable. Using the wrong wood flooring or installation methods over a radiant heat system though can be devastating. Unlike a conventional heating system which emits heat from the base of walls or up through a vent in the floor, radiant heat transfers the heat directly under and up through the wood flooring with temperatures of 80 degrees or higher. Due to the natural characteristics of wood, absorbing and holding ambient moisture, along with the ability of the wood floor boards to expand and contract with different moisture levels within its environment, the dry heat directly under the wood flooring can cause the flooring to dry out quickly and contract in size, causing cupping and/or large open gaps between the boards. Also, not all species of wood are good candidates for an installation over radiant heating. I do not recommend using Maple, Pine or Brazilian Cherry because they are noted to be unstable wood species.

Photo's courtesy of The Hardwood Council © 1999

There are several ways radiant heat systems can be installed.

By installing the radiant heat tubing directly under the wood subfloor from below. This is the most common installation in home renovation.

By installing the radiant heat tubing within a plywood underlayment system, directly over the existing concrete slab or existing wood subfloor.

By installing the radiant heat tubing within the concrete slab during the pouring of the concrete.

Any type of wood flooring used must be brought into the area in which it will be installed and allowed to acclimate for at least two weeks prior to the flooring being installed. We recommend the radiant heat be run at a temperature of 65-70 degrees two weeks prior to the wood flooring being brought in and until the wood flooring has been installed. Most newer radiant heat systems have exterior thermostats which will gradually bring up the temperature within the floor during the start of the colder season so that the heat will not shock the wood flooring causing the flooring to distort.

What is the best wood flooring to use over radiant heat?

FLOATING ENGINEERED WOOD FLOORS

The best type of wood flooring style to use would be a "Floating Engineered Floor." One of the benefits of using a floating floor is that the floor boards are locked together at the joints of each board and not nailed or adhered to the subfloor. This allows the whole floor to move as a single unit if a dimensional change within the wood floor takes place. Another reason is that an engineered floor with a stable plywood backing makes for a more suitable floor with less chance of dimensional movement than a solid wood floor. Floating engineered wood flooring can be installed over most all subfloors and surfaces (except carpet) as long as they are flat and secured well. Using a floating floor will drastically reduce any possible seam contraction (opening of joints) between the floorboards. There has been some argument that a floating floor will be more noisy when walked on compared to a nail down or glued down style of flooring. Personally I do not believe that to be always the case, but using a style that is 1/2 inch or thicker will be more sound deadening. There are also underlayment pads available that dramatically reduce sound transfer when walked on. Installing a floating floor is a very quick and easy installation for a "Do it Yourselfer." The boards are simply glued or (depending on style purchased) clicked together, thus eliminating the need of using nails or staples to secure the flooring to the wood subfloor - that may puncture the radiant heat tubing. There are many different styles and colors of floating wood floors to choose from.

DO MANUFACTURERS WARRANTY THEIR "FLOATING FLOORS" OVER RADIANT HEAT? Most floating floor manufacturers provide a warranty for installations over radiant systems (with the possible exceptions of their maple and brazilian cherry species), but the installation of their flooring has to be done according to their specifications (instructions are in every carton of flooring). The surface temperature of the subfloor should not exceed 85 degrees. A floor that is too hot can become dried out and distorted.

For more on "Floating floors" see our article - All About Floating Floors

The Floating floors recommend using are : Tarkett - The Longstrip collection - Artisan Plank collection, Anderson Engineered Wood Flooring - (specified styles), Kahrs Wood Flooring, Mannington Wood flooring

 

ENGINEERED WOOD FLOORING

(Non-Floating) Engineered Flooring can also be used. Again, because of the stable plywood backing an engineered floor makes for a more suitable floor with less chance of dimensional movement than a solid wood floor. Most engineered flooring can be direct glued, stapled or nailed down, but care has to be taken to avoid stapling or nailing the flooring down and puncturing any radiant heat tubing. I DO NOT RECOMMEND GLUING DOWN ANY FLOORING DIRECTLY TO THE EXPOSED RADIANT HEAT PIPING. Doing so may cause damage to the radiant heat tubes and be a big expense if the heating system has to be repaired. I ALSO DO NOT RECOMMEND DIRECT GLUING DOWN ANY WOOD FLOORING OVER A BRITTLE LIGHT WEIGHT CONCRETE. If direct gluing down an engineered wood floor is desired and the wood sub-floor has a radiant heat panel system (shown above) with exposed tubing, I would recommend installing a 3/8 inch underlayment plywood over the piping first. Always follow the manufacturers recommendations as to the installation of their flooring.

For more information about "Engineered Flooring" see our article - All About Engineered Wood Floors

DO MANUFACTURERS WARRANTY (NON-FLOATING) ENGINEERED FLOORS OVER RADIANT HEAT? Some manufacturers do, (with the possible exceptions of their maple and brazilian cherry species) some do not. The ones that do state the installation of their flooring has to be done according to their specifications (contained in every carton of flooring) and the surface temperature should not exceed a particular temperature. The surface temperature of the subfloor should not exceed 85 degrees. A floor that is too hot can become dried out and distorted.

The engineered wood flooring recommended using are:

Mercier Engineered Flooring, Anderson Engineered Wood Flooring - (specified styles), Mannington Wood flooring

Prefinished Quarter Sawn engineered flooring is also available

 

3/4" SOLID WOOD FLOORING OVER RADIANT HEAT? (NOT RECOMMENDED UNLESS ITS QUARTERSAWN)

If a Solid 3/4 inch thick wood floor is desired, it is recommended to use "Quartersawn" flooring (not available factory prefinished). "Quartersawn" is a method of cutting the boards from the log, so that the direction of the grain of the wood are vertical instead of horizontal (plainsawn). Quartersawn flooring is more stable than the commonly used "plainsawn" flooring because the expansion and contraction within quartersawn wood flooring is more vertical than across the width of the board. "White Oak" quartersawn flooring is very stable and is recommended to use. Also, if a 3/4 IN. thick solid wood floor is desired, using narrower boards is a better choice than using wider plank flooring because there are more seams to take up any movement within the flloor. Since 3/4 IN. thick flooring can only be nailed or stapled down, great care has to be taken to avoid puncturing the radiant heat tubing. The surface temperature of the subfloor should not exceed 85 degrees. A floor that is too hot can become dried out and distorted.

For more information on Solid Wood Flooring click here - All About Solid Wood Floors

DO MANUFACTURERS WARRANTY SOLID 3/4 IN. THICK FLOORING OVER RADIANT HEAT? There is no warranty provisions for 3/4 solid wood flooring warranty over radiant heat systems.

The Quarter sawn Wood Flooring recommended. - Custom Milled Unfinished Flooring

 

CAN LAMINATE FLOORING BE USED OVER IN FLOOR RADIANT HEAT SYSTEMS?

Using a laminate flooring (like Pergo) is another option. As the photograph of the flooring style is laminated to a dense center core that has very good stability. The surface temperature of the subfloor should not exceed 85 degrees. A floor that is too hot can become dried out and distorted.

DO MANUFACTURERS WARRANTY LAMINATE FLOORING OVER RADIANT HEAT? There are provisions for Laminate flooring warranties over radiant heat systems. Check with the particular manufacturer.

 

Laminate flooring recommended using:

Pergo, Quickstep, Armstrong, Columbia, Tarkett, Alloc

IMPORTANT: MOISTURE TESTING:

TEST FOR MOISTURE IN CONCRETE SLABS: Newly poured concrete slabs can contain a lot of water and should be allowed to cure for 60-90 days prior to having any type of flooring installed. All concrete slabs should be tested for moisture prior to installing any type of flooring. An easy way to check for moisture is to tape the edges of 3'x3' square pieces of 4-6 mil plastic sheet down in several different areas of the slab, wait 48 hours to see if any moisture (condinsation) builds up under them. If signs of moisture are present then the moisture problem has to be corrected first prior to installing any flooring. Moisture levels within a slab either on grade or below grade can vary during different times of the year depending on the ground water (water table). Due to this and depending on your particular environment you may have a problem later when using any direct glue down (non-floating) engineered floor because the adhesive used to glue the engineered flooring down may allow this moisture transfer to enter the wood flooring. Also, the flooring could become detached from the concrete slab. Floating floors are, in our opinion, the best and safest type of flooring to use. Using a floating floor allows you to create a barrier between any possible moisture later by laying 4-6 mil plastic directly over the concrete to act as a moisture barrier taping all joints with duct tape prior to the flooring being installed.

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