I decided to undertake a little plumbing project here at my office this week, and unsurprisingly, there were opportunities for mental growth (and some chemically destroyed brain cells) encountered along the way.
As you can see, the project was to transplant a small water heater from a building where it was no longer in use, into our office. We haven’t had heated water here since renovating and repurposing ‘this old house’ into our office space in 2006. We haven’t really missed it too much, but with the shorter days of winter, I’ve been itching to move my workouts to the early morning to help me get my days started with a little more energy. Having a place to shower up and change into work attire here at the office would be a big help in bringing that ‘itch’ to a reality.
So, after studying the network of existing iron pipe, I determined a suitable location for an emergency drain pan, and set about acquiring all the fittings and pipe needed to plumb the new water lines. I had always heard that CPVC was more appropriate for hot water applications, but didn’t really know what the difference was. Never being satisified with, “because that’s what CODE requires” as an answer – I set about getting the technical and practical answers to my questions:
A technical explanation of the differences that make CPVC special:
CPVC is PVC (polyvinyl chloride) that has been chlorinated via a free radical chlorination reaction. This reaction is typically initiated by application of thermal or UV energy utilizing various approaches. In the process, chlorine gas is decomposed into free radical chlorine which is then reacted with PVC in a post-production step, essentially replacing a portion of the hydrogen in the PVC with chlorine.
Depending on the method, a varying amount of chlorine is introduced into the polymer allowing for a measured way to fine tune the final properties. The chlorine content may vary from manufacturer to manufacturer; the base can be as low as PVC 56.7% to as high as 74% by mass, although most commercial resins have chlorine content from 63% to 69%.[citation needed] As the chlorine content in CPVC is increased, its glass transition temperature (Tg) increases significantly. Under normal operating conditions, CPVC becomes unstable at 70% mass of chlorine.
Various additives are also introduced into the resin in order to make the material processable. These additives may consist of stabilizers, impact modifiers, pigments and lubricants.
And a more practical explanation of why it’s required in hot water applications, and how it got it’s goofy sizing and color:
In the case of PVC, when it was first introduced into the plumbing trade in the mid 60’s it was approved for all potable water systems, both supply and distribution. At that time it was also a common practice to operate water heaters at or near 180degF.
It was soon discovered that PVC will exhibit wall softening and glue joint failures at temperatures approaching 150degF, which explains why the ASTM standard for PVC now limits it to applications not exceeding 140degF. )
The PVC formula was then improved upon to create CPVC which can withstand temps up to 190DegF for a short time.
Initially the codes were ammended permitting PVC in the cold water service, but requiring CPVC in all “Hot Water” applications, however this lead to a lot of confusion amongst the general public and it was soon discovered that homeowners and DIY’ers were erroneously using the PVC in applications that required CPVC. It must also be noted that initially CPVC was made in the same white color and to the same Sched.40 dimensional specifications as was the PVC which then lead to a lot of confusion by mixing both the pipe and fittings. CPVC is still made to sched.40 specs and the only method of distinguishing the two materials is to actually read the labelling printed on the pipe wall.
The CPVC that is commonly used for distribution piping today is not made to ASTM pipe Schedule standards, but rather it is CPVC-CTS, (Copper Tube Standard) which explains the difference in overall tube dimension.
Something to keep in mind the next time you’re futzing around up in your attic, playing with the sawzall and sucking pipe glue fumes…
Today, I learned! 