Everyone I’ve talked to who has in-floor heat says they love it.

Heat radiating from the floor feels like sun warming your back on a summer day.  And it sure beats convection current coolly wafting past you, blown from a distant forced-air register.

I’ve been told that people will comfortably set their thermostat to a lower temperature in radiantly heated houses.

We decided to install four big solar hot water panels in our back yard to bring in-floor radiant heat into Underhill House.

Concrete floors on both levels of the house seemed a good choice because they are the best home-building material for storing  radiant heat.  And our research convinced us that concrete was also the most efficient material for transferring that in-floor heat back to us on cold winter evenings after the sun goes down

Still, we were a little concerned — a few years ago we watched Doug’s dad jack hammer up his slab-on-grade concrete floor looking for a sewer leak.                                                                                                                                                                                                                                                                    Our fear was – WHAT IF WE GET A LEAK IN THE PEX TUBING EMBEDDED IN CONCRETE?

That would be bad, right?

So, guess what happened last week?

The weather was dipping down below freezing at night, and we had temperature-sensitive painting and plastering coming up.   It’s still going to be a few weeks before the solar hot water panels get hooked to the system, but the propane back-up was already in place, so it seemed like a good time to get it up and running.

But when Mark O’Neal from Full Spectrum Solar came out to make the final preparations, he discovered a leak in the PEX tubing.

Now here’s where today’s post becomes a detective story.

The first clue was that the drip was occurring right under the place where the tubing went through the basement ceiling up into the concrete of the main floor.

The upstairs tubing layout, designed by Andy DeRocher, was carefully arranged to keep all of the PEX lines away from points of attachment for wall framing.  It consists of six loops (12 tubes) that come up from the basement side-by-side under the threshold to our bedroom doorway and then fan out, traveling throughout the house.

This tree arched a bit to the north, displacing the bedroom door a few crucial  inches.

This nice, logical layout was complicated by the nature of a house built of unmilled branching timbers.  With a whole tree house, the paper plans have to be adapted to accommodate the actual posts and beams that are used.  You don’t come back from the woods with perfectly straight timbers, accurately sized down to the eighth of an inch the way you expect to when you buy dimensional lumber from the lumber yard.   Your final house resembles but does not exactly represent the blueprint.  Unfortunately, the dimensions of the branching post outside our bedroom doorway required the bedroom door threshold to be moved several inches north along the hallway wall.

The design change seemed fine for handling people moving back and forth into the bedroom, but no one remembered the PEX placed under the originally-planned threshold.

Moving the doorway a few inches to the north put the outer PEX tube into harm’s way. When the bedroom wall was anchored in place, the last PEX line took a direct hit from a powerful concrete screw and was winged by the next screw.

So when Mark filled the PEX tubes with warm water – drip, drip, drip!

It didn’t take long to figure out that the relocated doorway had caused the leak.

Michael, one of our carpenters, spent a day chiseling down to and around the wounded PEX.  Watching him work reminded me of an archeologist delicately locating and exposing the tibia of our petrified PEXasarus

There it was – a clear puncture wound and an inch or so further was a divot – just a graze — probably about a third of the way through the tube.

Mark came out the next day and brought an assortment of splicing hardware possibilities.  At first he thought he would repair it with the kind of brass fitting used to attach the PEX to the boiler.  That would have worked well, except it did not extend far enough to also cover that second, worrying nick.

He returned to his PEX repair kit.  One really useful feature of PEX tubing is that it is made of a substance called cross-linked polyethylene .  Cross linking is a chemical form of reinforcement – a kind of three-dimensional matrix that is used to emulate the fibers in fiberglass or the reinforcement bars in concrete.

Cross linking greatly increases PEX strength.

When heated, the PEX is clear and flexible. When it cools again, it returns to its original shape.

But it does more.  Unlike the static physical three dimensional matrices in concrete and fiberglass, the chemical scaffolding in our PEX tubing can be disconnected and reconnected in new configurations and, then when cooled,  return to its original shape with a fresh array of reinforced crosslinks.

You disconnect the original cross linkages with heat and create the new ones as the tubing cools back down.

Mark cut out the section of defective tube, then heated the cut ends and bent them up so he could slip another ring of PEX that has been expanded while it is hot over the break, and bend it back into line.  The tubing became translucent after heating, and then as it cooled, it became opaque and solid again in a straight line.  The PEX collar pulled into a very tight seal as it returned to its slightly smaller cool shape.

It’s an amazing material that made for an elegant patch!

Fortunately, the entire excavation took place in a spot where a wall will cover the intrusion.  Michael is going to fill the hole with foam insulation and then rebuild the frame.

Good as new!

4 replies

  1. HI! Great story! We are looking at a house right now that has the pex hot water hear under a cement floor. How are you liking both your heat as well as the cement floor? Did you do an acid stain on your floor? Thanks for any feedback you can give me.

    • So sorry about the long delay, Diane.

      We are loving the heat in our floors. It’s a very gentle, comfortable heat. The cement floor has pros and cons. The pros are that it REALLY does an amazing job of soaking up the passive solar heat and radiating it back during the evening. We are using very little fossil fuel in our propane backup system. It is also the most efficient way to transfer the heat from the PEX into the room.

      As far as appearance, we did not do an acid stain, and I wish we had. We were pinching pennies, and will probably ultimately color the floor when it is less convenient to do so. We are actually thinking about rubbing black walnut hulls into the floor and then resealing it. We have a lot of black walnuts on a good year. Last year was a bumper crop, but we didn’t have time to test it and do it. This year has been a very minimal crop, and I hate to take those few I see because I know the wildlife uses them.
      Maybe next year.

      As to the texture and hardness — it’s o.k., but not great. My husband walks around barefoot, but I prefer to were my cork-soled slippers in the house because it is a hard, hard floor, and you feel it if you are standing in the kitchen for a long time, or dancing about for over an hour.

      Every flooring choice has its pros and cons and after almost two years living withconcrete floors, I wouldn’t do it differently. They are going to be very durable. They provide amazing thermal mass, and they have an interesting, basic look.

      Good luck with your choices,

  2. The only downer with the heat is if it gets hot during the day from the sun or what ever you can’t just turn down the thermostat cause it takes about 12 hours to lower the temp. In the slab, also takes the same to raise the temp. We found it’s easier to open a window to cool the house during the day if needed.
    But I still think it’s the best way to heat a house…..

    • Hi Bruce,
      Thanks for your comment. I agree totally.
      Our construction manager described homes like ours as “Passive solar — Active owner.” There is more to managing the temperature of a passive solar home than dialing the thermostat up and down.
      The shoulder seasons of spring and fall, when the sun low enough to pack a real wallop and still slip under the eaves that protect us in summer can lead to a warm house sometimes, and we do the same — open the windows. I actually love being able to flood the house with fresh air and listen to the birds and the wind on those occasions.
      Yesterday, when it was in the 20s outstide, the sun brought our place up to 72 by noon. Then the sky clouded over, and we coasted on that absorbed heat for the rest of the day and night. Still 61 in here this morning. I enjoy the variations.
      A passive solar house is kind of like an organism responding to the sun, and you have to tune into it. I enjoy that.
      We’ve been through two turns of the seasons here now, and I like it much better than the conventional houses we have lived in in the past.

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