In the course of my previous job with the RPA, I helped develop a national standard as it pertains to hydronic piping called the ASSE 19210 Hydronic System Installation Standard.
Within that document, we address the coefficients of expansion AND contraction, which are 1.1” per 100 foot length per 10 degree F. I make that distinction (contraction), because in my 40 years of working with hydronics, I witnessed a snow/ice melt system that we had piped through a crawl space between the heat source and the heat load (driveway). When started cold, fluid coming back off of the slab can be below freezing. The PEX tubing contracted so much that it tore itself away from all of the plastic pipe supports we’d used in running it across the crawl space ceiling. This is not something that would normally cross the minds of people installing PEX, because we are aware of expansion potentials, but not the contraction potentials. This tubing growth potential gate swings both ways.
Depending upon the application, all expansion take up or compensation devices need to initially be “set” to a given position, depending on whether it will be accommodating expansion or contraction. If it is compensating for contraction, then the legs of a U joint would need to be somewhat “negative” or closed (closer to each other) so that when contraction hits, the joint goes to a “neutral” condition. If it is to accommodate expansion, then the legs of the joint will need to be somewhat “positive”, or bowed outward, so that when expansion hits, the joint will be neutral. If the joint will be accommodating both expansion and contraction, then it would need to be preset in the “neutral” position. The ambient temperature at the time of the installation also needs to be taken into consideration when “setting” an expansion compensator. If work was being done and the space is within 20 degrees of anticipated final conditions, you are OK. but if it is greater than 20 degrees hotter or colder than it will finally be, you may need to compensate for this ambient condition.
In teaching these classes, I emphasized to my students that PEX has an extremely high coefficients of expansion and contraction that must be controlled in order to avoid issues. The methods of control or compensation are exactly the same as the ones we’d use for copper or other non-plastic pipes, but require much more forethought due to the significantly higher growth potentials. I always require my long PEX runs to be anchored in one or more spots, and then send the growth potential to a place where it will safely be accommodated. Accommodation can be as simple as the well-known long legged U bend, or the use of a full 360-degree loop, or as simple as allowing adequate “end free play” to accommodate this known expansion potential. Regardless of the method chosen, we MUST anchor the tubing at some point, otherwise the growth potential does what it wants to, and not what you wanted or expected it to do.
Regardless of the method chosen, we MUST anchor the tubing at some point, otherwise the growth potential does what it wants to, and not what you wanted or expected it to do.
Side branches coming off of a large bore main are tricky, because you don’t want to cause stress on the side branch due to binding caused by the growth potential of the horizontal main, all while maintaining a sealed penetration (code required draft and fire stopping) and I’ve found that having extra length to allow some flexing before the branch penetrates the structure will avoid any stress being imparted to the branch piping. It all requires a little extra thought.
Not addressing this potential will cause a lot of unnecessary noises, as the tubing comes into contact with the floor joists in which it runs. Most EVOH barriers cause a loud squeaking and ticking sound as they move through the floor joists. By anchoring the tubing, and controlling the direction of growth towards a safe haven for the expansion growth, you will lessen the amount of expansion and contraction. An additional recommendation, that isn’t covered within the codes, is the need to provide tubing “gluides” where it goes through the wooden structure. This is a combination glide and guide, hence the term gluide. There are some suspension clamps that can serve in this capacity, but they have to be screwed down in such a manner that they don’t actually clamp onto the tubing, causing it to bind up and grow in a direction you hadn’t anticipated. I use a polyethylene liner made from extra heavy moisture barrier poly plastic or cut up white plastic milk jugs. It allows the tubing to slide through the holes, causing tube binding and associated noises, and allows the growth to grow towards the intentional point of accommodation.
Additionally, not properly installing this tubing can result in unnecessary wear and tear on the piping, and is almost guaranteed to be noisy, which is not a part of the definition of comfort. Done right, PEX systems can be just as quiet and dependable as a metal pipe alternative. Done wrong, the consumer will be constantly hearing ticks, clicks and squeaks associated with their distribution piping every time their systems starts up or shuts down. Doing it right doesn’t take a whole lot longer, but will result in a nice quiet system with little to no complaints from the consumer. Doing it wrong will result in the consumer telling 10 friends of their negative experience, and that 10 people will tell ten people and so on and so forth.
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