Installing solid hardwood flooring over radiant floor heat.

Can you install solid hardwood flooring over radiant floor heat? That was the pressing question after I had installed radiant floor heat in the new living room using the “DryAbove” method by HeatLink. Briefly, over floor joists or rigid foam on concrete, the DryAbove method entails laying down one layer of ¾” plywood and then in the opposite direction install 6-3/4” sleeper strips of ¾” plywood on 8” centers. This will leave a gap of 1-1/4” for the PEX tubing and metal heat transfer plates. After doing this to your floor, you look at it… and wonder, what in the heck am I going to put over it?

Obviously you should have an idea of what you’re going to do before starting the DryAbove method. Like so many things before, in my home building dream, I sort of had an idea. From what I had read, the best way to go was with laminated manufactured flooring. The floating install kind. Lay it down and let it move with the heating season. I knew I could do that for sure but what I really wanted to do was install ¾” solid hardwood flooring… but I was afraid. I was afraid of pounding all those nails and fearing one would go through the PEX tubing by mistake. The horror! For me, that was where the controversy lay and what, at times, kept me awake at night. (I was not concerned about whether the heat coming from below would affect the flooring because I had seen a YouTube video with a team of guys who power-nailed down solid hardwood oak over radiant tubing, so I knew my dream was possible).

But spring had sprung and there were more pressing issues outside in my home building quest, so I had time to think about it. I just bought some 4×8’ x ½” plywood and temporarily covered the radiant heat tubing with that so I could walk on the floor. The plywood came to good use later.

In the meantime, on the Internet, I looked at the installation guidelines from a couple of manufactures of solid wood and laminated flooring. When it came to radiant floor heat, the laminated guys were cool with it for floated installation but most solid wood manufactures were not thrilled. The hardwood people said it could be done with precautions. Precautions like the water temperature under the wood floor should never go above 88°F, (some say lower), and never below 60°F. I thought that’s fine, because the mixing controls for the radiant heat water temperature was not supposed to go over 88°F anyway. The below 60°F part was a different matter because this is a second home and I lower the thermostat to 50°F during the times I wasn’t there in winter. I was talking to my sawmill friend Bandsaw Bob, who had put down laminated wood flooring in his dinning room and living room and said he wished he hadn’t. He said he didn’t like the sound it made when walking on it. He said it sounded plastic. The kind I put down in my city apartment didn’t sound like that but it was real cherry laminated on top of 3/8” plywood, soft and very easy to dent. It also moved sometimes and I didn’t like that. People loved the look of it and Deb’s yoga clients thought it was perfect because with the underlayment pad, it had some give. But that is not what I wanted in my “authentic” country home in the mountains.

From the time I left the flooring project, till I picked it back up, three years had passed. When I got serious again, the big issue for me was no longer, “Can I put solid hardwood flooring over radiant heat?” but, rather, “Which product do I like better?”  After a yearlong quest of going back and forth between laminate and hardwood, I went with hardwood. From Home Depot I special ordered, Blue Ridge, Oak Driftwood Brushed, 5”x3/4”, solid wood flooring at $4.99/sq. ft.

3/4″ Oak has an R value of 0.64. So it is a good material for radiant floor heat transfer compared to others. I liked the novel look of 5-inch wide planks and figured there would be less nails pounded and less chance to put one through the PEX. I wanted to do the installation at the end of the winter heating season so the house was good and dry. That way the floor would be as tight as possible.

I let the flooring acclimate in the living room for over a month. When I opened a box and pulled out the data sheet I was hit with a nasty surprise, the manufacture did not recommend putting it down over radiant floor heat. Why didn’t I check that out before? I did but it was three years previous and not with Blue Ridge. The main problem was the boards were wide and not the narrow strip kind. On the Internet the manufacturer went deeper into why you shouldn’t install it over radiant floor heat and it wasn’t good. All hell could break loose by their description, splitting, cracking, and boards popping, all kinds of destructive things. I had like 16 cases of this stuff in my living room for over a month, $1,600 worth. My wife and I both loved the look. I wasn’t taking it back.

You know when lawyers get involved sometimes a small problem becomes a big one. It was about a risk. I’m sure the lawyers told the manufacture to stay away from it for liability reasons. That is what I figured the situation was here. I have installed oak hardwood, narrow strip flooring before, in the guesthouse, over rigid foam insulated concrete on sleepers. The house would freeze to as cold as 20°F when I wasn’t there. Then I would come back in the winter and blast the wood stove, heating the room up to 70° in less than 5 hours. That flooring is fine after 15 years. Upstairs in the main house, I installed over 200 sq. ft. of wide plank, 9”x 7/8”, solid maple flooring that I had harvested from the property and milled myself. The house would freeze when I wasn’t there, I would show up, blast the place with a woodstove furnace, do this over many years and that wide plank maple is as good today as it was when I installed it.

9 inch Wide Plank, Hardwood Maple being installed in the 2nd floor bedroom. The maple was harvested from the property, sliced up by BandSaw Bob, planed and kiln dried by me. A detailed description of this is explained in another post.

So I’m thinking how bad could this radiant heat be? The go ahead clincher for me was the fact that I would be nailing this flooring onto what was essentially a floating plywood floor. Floating over 3-inches of rigid foam insulation on concrete. So I figure the whole thing will move together if there is any expansion stress from the warming. The other thing is that radiant heat is slow. When you go from 50°F to 70°F it takes hours. So any expansion was going to be slow as well. Manufacturers are also concerned about the moisture content of the wood and adding heat from below affects that. If one side is dryer than the other cupping or splitting can occur. All I can say about that is I use my EPA approved wood stove in winter when the house has cooled down significantly to bring it back up to 68°F and save on oil. Sometimes I use it for a burst of warmth or atmosphere. This dries the house out so any heat from below is only going to equalize what is going on above from a moisture content perspective. I wasn’t stopping now- to hell with damn lawyers and maybe common sense.

What ever flooring you choose it needs to be installed perpendicular to the predominate PEX run.

Getting started is the hardest part. In my case the supply lines were running parallel with the flooring. The first course could not be nailed down because of the PEX so I used flooring adhesive. I didn’t want to add a transition saddle so I ripped the bottom tongue off with a table saw. This gave me just enough space to overlap the tile.
The top tongue was sanded down to make a smooth bevel. This transition wasn’t an accident, I planned for it. As of this writing it has been over a year and the glued down transition plank has not moved. Long term, if there is ever a problem here, I would countersink four square drive, stainless steel screws, evenly spaced down the middle of the starter strip. This photo documentation will remind me where the PEX is.

Installing hardwood over radiant floor heat.

2 1/4″  7D flooring nails.
Love my Estwing 16 oz. hammer.

I decided to hand-nail this job so I could stay focused on the PEX. Pilot holes were drilled for each nail and then counter sunk.
It would be hard to make money doing it this way.

I ripped a couple of angled wedges to persuade any errant boards tight.
I had very few reject boards and was extremely satisfied with the Blue Ridge product. Good variety of lengths in each box to make a nice random look.

One thing I made sure was that there was plenty of expansion space around the perimeter because of the radiant floor heat controversy. That includes the plywood sub-floor perimeter spacing also.

Finished floor. I was very happy with the way the transition worked out between the kitchen tile and the living room floor.

I still need to mill some hardwood cherry for the baseboards and window moldings.
It will happen!!!

Epilogue: Because of the fact that this is a second home and the temperature fluctuates so much from when I am at the country house and away, I do take precautions in regard to the solid hardwood flooring when heating the cold house up. First thing I do upon arriving is start the wood stove. That is in the kitchen area and surrounded by ceramic tile and a masonry wall.

EPA approved US Stove King 89,000 BTU with blower, from Home Depot.

I let the heat build up for a couple hours, more or less, depending on the outside temperature. In the living room, where the thermostat is, the temperature will start to rise becasue I have a duct-work blower system that circulates hot wood stove air, through there, the bedroom and the kitchen intake area. Most often the thermostat was set to 50°F while away to save on oil. When it starts to get around 58°F I change the thermostat to 60°F, causing the oil fired boiler to fire and start circulating warmer water through the floors. Basically it starts chasing the wood stove so they work together till the room temperature reaches 68°F, or whatever I want. This way I think it eases the stress on the flooring. So far it has worked. The floor is fine. I will update this epilogue in years to come. I am not worried.
No one ever said having a second home was easy.

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