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Thermal Properties and Benefits of Polyethylene (PEX) Piping

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Thermal Properties and Benefits of Polyethylene (PEX) Piping

Engineering Advances of Polyethylene (PEX) Piping

There is a common saying that goes: out with the old and in with the new. This brings me to the topic for this week’s blog. I will discuss the benefits and disadvantages of using cross-linked polyethylene, better known as PEX, in standard plumbing applications, most notably for potable water. PEX is a high-density material, in which the molecules are “crosslinked” during the production of the pipe. This process allows for the pipe to have increased thermal management properties and the ability to be used in higher temperature and pressure applications, than compared to the standard polyethylene material. The thermal conductivity of PEX (Btu in /h ft2 0F) is 3.2 Btu, much greater than other thermoplastics, with a maximum temperature limit (0F/0C) of 210/100.

[i] While polyethylene pipes have been used for many years, mostly in radiant heating applications, there are quite a few factors for its expanded role in commercial and residential plumbing. For decades, copper pipe has been an extremely common material in the plumbing world, and while copper pipe is still used for the majority of new buildings, PEX has seen a significant increase in use within the last few years.

Listed below are some of the pros and cons of using PEX piping as compared to the copper pipe alternative.

Cost Effectiveness

The cost of copper piping has skyrocketed in the last ten years, mostly due to supply and demand. When Hurricane Katrina struck New Orleans in 2005, the demand for building materials to rebuild the city was something that was felt all across the country. Not only did prices surge due to material shortages, the theft rate at building sites increased as well. The copper being used would be stolen and resold as scrap. With the increase in building material costs came increases in home prices. With our current lackluster economy, many builders have been looking for ways to decrease building costs. PEX piping is just one of those ways as copper pipe prices in some areas saw increases of four to five times the norm. PEX piping costs can be as little as one-fifth that of copper. PEX piping is also a very flexible material, and due to this fact, installation requires fewer fittings when changing directions for runs, again lowering installation costs.

Installation

As noted above, the flexibility of PEX allows for longer runs without utilizing fixtures. The use of fewer fixtures reduces the opportunity for leaks to develop as well as quicker installation times. Unlike copper pipe that requires long branch runs that tee off to service multiple fixtures, PEX system installations will generally run individual branch lines to each fixture from a manifold set up. One of the benefits of this is that you only have to shut down a single line if repairs or service is needed, rather than draining the complete system. This not only leads to convenience and cost savings, but it also reduces the amount of water that may be wasted during testing or repairs. See figure 1 below.

PEX_Layout_1

Fig. 1

Basic layout of a PEX water supply installation

The last major benefit is that torches and heavy metal cutters are not needed for PEX piping. All that is needed for installation or repairs are cutting and crimping tools. This leads to big advantages in safety and efficiency while working in small spaces.

Durability / Reliability

While there are many advances in PEX piping, it does have a few durability concerns as compared to copper. Obviously it is a plastic, and will puncture much easier than copper. During installation, the pipes plumbed within walls must be better protected from errant nails or screws than the rigid copper pipe. PEX is also negatively affected by UV rays and therefore cannot be used where sunlight is directly present. This exposure will degrade the PEX material quite quickly and therefore limit its usefulness in exterior applications. While PEX has been tested to have a working life of 50 years, the average warranty on the product is only 25 years.

While I do not believe PEX will overtake copper as the main material used in plumbing applications, I do think that we have yet to see the full potential of what PEX brings to the table. With building expansion and costs rising, it is safe to assume that PEX piping will continue to see an increased role in the plumbing and building trades.

 


[i] http://www.engineeringtoolbox.com/physical-properties-thermoplastics-d_808.html

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