“I know wood flooring should not be used ….”
“I know wide plank is not recommended over radiant heat, but my customer wants to put 6” wide plank over the system.”
“I know engineered flooring is the only wood product that can go over radiant heat systems, but….”
“The manufacturer does not recommend their product for radiant heating systems…”
“The manufacturer says the water temperature in radiant systems with wood flooring should not exceed 85 degrees.” …and so on...
Let’s start by saying that with proper customer expectations most any wood flooring product can be installed over a properly designed radiant heated flooring system with the normal caveats in practice, i.e. don’t put solid wood below grade; nailers should be 12” o.c. and less; solid flooring and wider widths require a solid subfloor; etc.
As you see, most of the items deal with solid wood. However, engineered flooring can also be a good choice over radiant heating. Since most engineered flooring is proprietary and general directives may not apply to the specific product, the manufacturer’s directives should absolutely be followed. In any case, if the manufacturer does not recommend or warrant their product over radiant systems, DON’T INSTALL THEIR PRODUCT in such an application.
The second floor system - I joists 16” o.c.; 3/4” square edged plywood subflooring; 2” x 4” SYP sleepers 12” o.c. parallel to joist direction glued and screwed to plywood; between sleepers-Maxxon tubing 9” loops imbedded in Maxxon gypcrete to top of sleepers. The flooring-- one bedroom with 4” cherry plank, one bedroom with 2 1/4” ash strip flooring, and the loft area with 2 1/4” quartered white oak strip flooring. The ash flooring was finished with a water-based urethane. Other floors were finished with a hand rubbed sealer and wax.
As a flooring contractor you will likely either place the sleepers before the tubing or draw out the sleeper location before the tubing is placed. In either case, make a list of items the heating contractor should follow for proper tubing location for the flooring. You don’t want a tube to be placed where you absolutely have to fasten the flooring. If you don’t communicate and accommodate each other’s requirements a problem floor is likely. The flooring contractor is the last one there, so the blame can easily point to you. With the sleepers down, the gypcrete was poured. Before the flooring installation began, some of the gypcrete was higher than the sleepers and had to be disc sanded with 24 and 30 grit to a flatter condition.
The main floor system - This is a staple up system with the tubes attached to clips on the underside of the plywood subflooring with insulation between joists. This flooring was installed during the spring right after the upstairs was completed. The great room is 2 1/4” and 3 1/4” alternating white oak strip; the kitchen and breakfast areas are 2 1/4” hickory/pecan strip; the master bedroom is 5” white oak plank; the entry is 2 1/4” quartered white oak strip; and the dining room is an octagon patterned floor of hickory/pecan strip and 4” plank. I used 1 3/4” cleats for the flooring installation to assure no heating tubes could be punctured. I did not use staples since noticing that staple legs sometimes run out of the subflooring at odd angles and might hit a tube. I used felt paper only under the great room, entry and master bedroom.
Over the last five years I have observed the following: the upstairs floors - these rooms are generally more consistently warm during heating season; the rooms also have lower ceilings which likely contributes to the comfort. The sealed and waxed quartered strip flooring and 4”cherry plank show some gapping during the winter. The gaps are not prominent and generally close during the summer. The ash floors developed some noticeable permanent gaps that exhibit panelization about every 5 to 6 boards. (Photo 4) This was the only floor finished with a water-based finish and the only one showing panelization. The white ash coloration also shows the gaps more readily than any of the other floors. Some of this gapping can be attributed to installing the flooring at a somewhat elevated moisture content. I do notice a slight crowning each year when the heating system is first turned on but this flattens after about two weeks. During the winter the floors average 6 1/2% to 7% mc and 8% to 9% during the summer.
Also, with engineered flooring length shrinkage or end gaps may occur. I have noticed some manufacturers require that the relative humidity be maintained above 30 to 35% at all times for their product to perform properly. This may be a difficult requirement where extended heating is required. In addition, again if the manufacturer does not recommend their product over such a system don’t use that product. I am really pleased with my floors, and the subtle warmth without blowing forced air is a pleasure.