Radiant Heat Tubing - Cross-Linked Polyethylene or PEX
If you have hydronic or water-based radiant heat tubing system installed in your house, or contemplating to have one, then it may be vital that you understand how it works. Because a hydronic radiant heat system will run warm-water through plastic or copper tubes under your house, or perhaps in your ceiling (as the floor of the second story).
System basics of radiant floor tubing
This system of heating has been in place from the 1930s and after. The first system had hot water running through the copper radiant floor tubing to heat the floors. But since copper deteriorates sooner or later, the radiant floor tubing changed to plastic, which is much more durable. The most common plastic tubing today used in hydronic radiant heating system is PEX, or cross-linked polyethylene.
What is PEX radiant heat tubing?
PEX, or also sometimes termed XLPE, tubing is made from high-density polyethylene (HDPE) with bonded cross-links in the polymer, making it thermoset instead of the usual thermoplastic kind, but retaining the characteristics of thermoplastic tubing. A thermoplastic item is one which melts at a certain temperature and turns hard and glassine when cooled. They are usually polymers with high molecular weight. Thermoset items, on the other hand, do not change once they cure, which is accomplished mainly through heating, chemical action, or via irradiation.
Crosslinking, meanwhile, is achieved by increasing the bonding of the material’s macromolecules, creating a more complex structural form than that of standard polyethylene. There is PEX tubing designed just for plumbing, and PEX tubing designed specifically for radiant heat. Make sure you get the right type of PEX for your needs.
The other uses of PEX tubing
Because of its excellent characteristics, PEX tubing is also used, aside from in radiant floor tubing systems, in piping potable hot or cold water in households, as conduits for certain liquid chemicals, in natural gas and offshore oil requirements, in piping sewage and other slurries, in kayak and canoe hulls, in artificial joints, as dental filling material, and as insulation tubing for high-tension electric cables. As electrical cable insulator, PEX tubing can withstand currents as high a 380kV AC and hundreds of volts in direct current.
Different types of PEX tubing
There are generally three kinds of PEX used as radiant floor tubing: PEX, Barrier PEX and PEX-AL-PEX.
The first is standard PEX tubing, with all the attendant properties. The second has an anti-oxidation surface coating that allows it to be used where ferrous metal like cast iron is present. This type of PEX tubing is most commonly used in concrete applications.
PEX-AL-PEX incorporates an aluminum layer between the plastic inner and outer tubes, to serve as chemical and oxygen barrier as well as help retain heat longer in the tubing. This type of radiant heat tubing is used most often in subfloors, but not embedded in concrete. For systems like Warmboard, PEX-AL-PEX is used because it retains its shape after being bent. This is also nice because PEX-AL-PEX doesn't expand or contract as much as its counterparts, which means it stays in place and doesn't move in the flooring.
The disadvantages of PEX as radiant floor tubing
As perhaps everything else, PEX as radiant floor tubing material has its own problems, both in the material and as after-effects. One such disadvantage is expensive tools. Unlike for ordinary copper or galvanized iron tubings, the tools required in installing and repairing PEX radiant floor tubing are rather expensive, and that would have been a major disadvantage except that they are one-time costs.
Internal use only. PEX deteriorates quickly when exposed to sunlight or to extremes in weather. Thus it is recommended for interior or underground radiant floor tubing use only. It is not recommended for solar radiant heating systems.
It can generate water contamination. In areas where pre-2001 PEX tubing was used in radiant heating, extremely high levels of t-butanol and Methyl Tertiary Butyl Ether (MTBE) were detected. It turned out the chemicals were leaching out from the PEX tubing and mixing with the water if the water remained stagnant for a period of time in the radiant floor tubing.
However, not all PEX tubing has this fault, and more modern manufacturing systems of PEX tubing have conceivably surmounted this problem.
Encourages bacterial growth. Somehow the plastic’s characteristics help bacterial growth when water in the radiant floor tubing is left stagnant. When the heating season is over, we recommend flushing the system of water no problems occur in the summer months.
Rodents like it if it is exposed. This isn't a real big problem unless you leave the construction site unattended for months. Rodents like nibbling at it, actually, which can cause leaks. But since most of the PEX radiant heat tubing is underground or inside the house and covered by insulation, this is only a problem for people who don't properly install PEX radiant heat tubing.
Yet for all the small problems, PEX radiant floor tubing remains to be the top choice for radiant heating by homeowners and professionals because of its many advantages. Perhaps it is time you should look at them, too?
- PEX Radiant Floor
- PEX Supply
- Radiant Water Heat
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