Radiant Heat Installation: Questions Answered

In response to a few questions on the NWFA Listserve:

Your question regarding radiant heat is a great one. This type of heating continues to grow all over the country. Currently close to 30% of our solid hardwood floors are installed over radiant heat and in some markets the numbers are even higher than that. I would have all the confidence in the world putting our Antique Oak over radiant heat as we do it every day; however, you do have to be careful as the Antique Wood Market is very fragmented and the quality can range drastically.

Radiant heat—in and of itself—is not bad for wood floor. All floors, including antique wood, should be kiln dried and during this process they are subjected to much higher heat than any current radiant heat systems, especially given the radiant heat systems of today. You have the advantage of running your tubes closer to the floor which means it should be able to run at a lower temperature and still achieve the heat your require.

However, there are still many variable that will affect the temperature of your system: how close together are the tubes? How high are the ceilings? How many windows are there? Etc. Often people cut costs and reduce the tubing/wall insulation which forces the system to run at higher temperatures, which may cause a variety of problems if the temperature is too high.

All in all, I see the problems with wood floors and radiant heat falling into the following categories:

1. Far and away the most common problem is that the radiant substrate is not acclimated (allowed to come up to the temperature you plan to live at) prior to installing the floor with the Radiant Heat system turned on after the install. When the heat comes on it will push any excess moisture out of the substrate and into the finished floor. This will cause the floor to temporarily expand and potentially buckle. However, if the radiant system is turned on in advance of installing the floor it will eliminate the moisture before the wood is installed. Regardless of having radiant heat or not…the moisture content of your subfloor should be within 2% of the moisture content of your finished floor before starting the installation. This can be achieved by turning on the radiant heat.

2. The second most common problem is Improperly dried wood flooring. This is especially common with antique wood as people think kiln drying is not necessary given its age. However, we have 200 year old wood that still has a moisture content of up to 18%. The trick is how to get all of the pieces at an even moisture content. Simply kiln drying it won’t work as it will dry some of the boards to the proper moisture level of 8%, but the higher moisture content material won’t be dry enough. To fix this problem, we actually introduce moisture into all of our antique wood to bring it up to the highest common denominator and then dry it down, to guarantee consistency. Without using this technique, you may put boards into your floor with a 15% moisture content that, when they dry out, will cause large gaps to appear.

3. The third most common problem is using a poorly engineered radiant systems. People cut initial installation costs and spread the tubes out. The systems then have to run water through the tubes at a much higher temperature (120+°F) where, in a system that is properly engineered and installed, would run at 90°F.

Simply put, heat is not the “enemy” of wood, water is. If heat is causing excessive drying then gaps will appear, but if subfloor and finished floor achieve “live in conditions” prior to installing the floor the heat will not move any moisture and therefore will not affect your floor.

Acclimate your subfloor. Acclimate your system. Use a well designed radiant system and —most importantly—use a high quality wood floor that is properly dried and you can have the same successful results we have in over 1200 radiant heat install per year.

Posted on September 24, 2008 at 09:13 AM in Hardwood Flooring • (1) Comments

Comments

Rick Menard said…

If your heating system throughout the home has been on long enough to
acclimate all of your flooring area, you should not see any difference
in your floor in the different heated areas. Once the sub-floor has been
acclimated to the radiant heat, it should be at the same moisture
content as the rest of the sub-floors in other areas of the home.

Please keep in mind different heat will cause wood to move a LITTLE
differently. For example, forced hot air will tend to dry wood flooring
out a little more closely to the vent areas as will a gas or wood
fireplace closest to those heat sources, causing a slight gap here and
there.

Some times we get too hung up on worrying about a little gap here and
there, but in my eyes, part of the beauty of wood floors is see
individual planks and character of how the tree grew. There is nothing
more beautiful.

Posted at 02:58 PM on September 24, 2008

Cherry Blossoms

Washington, D.C.

Carlisle Wide Plank Floors