Well, not quite yet, but we are getting ready for it. I am talking about the hydronic heating system in the basement floor, also known as radiant floor heat.
To get to the radiant floor heat, we have to install ½ inch cross-linked polyethylene tubing (commonly known as PEX tubing) that will be encapsulated in the basement concrete floor.
The material properties of PEX tubing make it ideal for radiant floor heating systems. It also begins to replace copper tubing in domestic plumbing systems, local building codes permitting.
PEX has an incredible resilience, with two exceptions. First, it degrades under the exposure of UV light. Most product information advises to keep the exposure of the tubing to daylight to less than 90 days. It is needless to say that the less it is exposed to any light, the better.
Secondly, it degrades on the exposure of radical oxygen molecules, which are occasionally found in water. Because of that it is recommended to use PEX tubing for hydronic heating systems with an oxygen barrier.
We would like the tubing to last as long as the concrete floor!
The radiant floor heat in the basement is organized into several zones. Each zone serves different heating or temperature needs.
All the tubing originates in the utility room, where will have the hot water source for heating, and returns to the utility room. Eventually we will connect the ends to a manifold.
The first two lines along the floor edges are spaced 6 inches apart, delivering extra heat along the foundation walls, which mitigates their potential cooling power. All other lines are then spaced 12 inches on center. The spacing is easy as we can use the six by six inch grid of the welded wire mesh as a guide.
We attached the tubing to the welded wire mesh with four inch zip ties at the recommended spacing of every two feet.
To control cracks in the concrete floor, we have planned expansion joints at various locations. At these locations, we run the PEX tubing through a PVC sleeve. The sleeve is the sacrificial lamb, protecting the PEX tubing from stresses caused by any cracking.
It is also recommended to protect the PEX tubing with PVC sleeves wherever it transitions in or out of the thermal mass, i.e. the concrete floor.
This is the case in the utility room where the lines originate and terminate (see image above) and where the lines transition out of the main basement into the porch area (see image below).
The pressure test
Very good! The PEX tubing is in place. Tomorrow, there will be a bunch of guys running around with equipment pouring the concrete over the tubing. But what if we damage a line and cause a leak during the concrete pour?
If that happens, we want to know about it right away, not after the concrete has cured!
Solution: connect all loops with compression fittings, set a pressure gauge on the last line, put the system under pressure and monitor the pressure during the floor installation.
Done! I got the bicycle pump out, put 30 psi on the system, and we are ready for the concrete the next morning. Except – when I showed up, two hours before the concrete arrived, the pressure had dropped to 10 psi. I wasn’t sure what to make of it and call Mariusz, our plumber, in a panic.
He pointed out that it is very unlikely that I have a leak in the PEX tubing and recommended that I check the compression fittings for a leak.
Our neighbor, who was up early, supplied me with soapy water in a spray bottle. Before long I got a big soap bubble around the culprit fitting and had it fixed. I pumped the pressure back up to 20 psi, and this time it was holding for good.
Actually, after the concrete pour, the pressure rose to 22 psi due to the heat in the concrete from the curing process. Let’s call that airtight!