What is PVC?
PVC (polyvinyl chloride) pipe and fittings are commonly used for plumbing, as well as venting and drainage applications. PVC is available in schedule 40 and schedule 80, with the difference being that schedule 80 is thicker and can handle higher pressures. Both schedules are resistant to corrosion and chemicals. Although PVC’s strength, durability, and low cost have made it one of the most widely used plastics in the world, some applications need something even stronger. That’s where CPVC comes in.
What is CPVC?
Except for one distinctive difference, CPVC is made up of the same basic elements as PVC. So what’s the difference? Spelling it out actually gives that away—CPVC stands for chlorinated polyvinyl chloride. So, CPVC differs in that it undergoes a free radical chlorination reaction, which increases the chlorine content of the material, hence the “C” as the first letter in the acronym, standing for “chlorinated”.
In the process, a portion of the hydrogen in the PVC is replaced with the chlorine. This is done by taking chlorine gas and decomposing it into free radical chlorine, which is then joined with the PVC.
The replacement of hydrogen with chlorine allows CPVC to withstand higher temperatures than PVC. While PVC can only withstand temperatures up to 140⁰ F, CPVC is capable of enduring temperatures up to 200⁰ F. Temperatures above 140⁰ F can weaken and soften PVC. Since commercial and industrial applications typically involve temperatures over 140⁰ F, building codes for those applications usually require the use of CPVC.
If you see schedule 80 CPVC, understand that it is different than schedule 80 PVC. Schedule 80 refers to the thickness of the pipe, and CPVC refers to the chemical makeup of the pipe. Therefore, schedule 80 CPVC is able to tolerate the PSI levels of schedule 80 PVC, which vary depending on the size of the pipe, while handling the temperatures of CPVC (200⁰ F).
Beyond the Chemical Makeup
The differences in chemical makeup can sometimes mean you need to use different primers and solvents. Chemical welds require a solvent primer, which softens the inner surface of the union and the outer surface of the pipe, and solvent glue that melts the contact areas together to create a permanent bond. The softening action of the primer allows better penetration of the glue. In order to create a strong joint, the primer and cement must effectively soften and melt the plastic. Since CPVC has a different chemical makeup, it uses different, high-strength solvent cement.
The sizing standards can also differ between PVC and CPVC. PVC has its own sizing standard in North America called Nominal Pipe Size (NPS). While schedule 80 CPVC is also labeled in NPS standards, CTS CPVC is measured using the Copper Tube Size (CTS) system.
So how do you know the difference between schedule 80 CPVC and CTS CPVC? The coloring of the pipe can be a clue—schedule 80 CPVC is often a light gray color, while CTS CPVS is an off-white/yellowish color. However, these are not necessarily industry standards, and the only sure way to tell is to check the labeling on the pipe.
Which Pipe is Right for Your Job?
PVC is used in cold water applications. It’s also used in vent and drainage systems. CPVC is used if the applications’ temperature is between 140⁰ F and 200⁰ F. That being said, CPVC has become widely used for both hot and cold potable water. CPVC has a wider range of applications, and it’s well suited for both commercial and industrial applications. Since it is more durable and has such a wide range of applications, CPVC is more expensive than PVC. However, it is still cost-effective compared other materials, like copper or iron.
If you are working with plumbing in your home, building a cold water plumbing system, or building a vent and draining system, PVC is generally the best option. It’s generally capable of handling these applications and is more budget friendly than CPVC.
The biggest thing to consider is the chemical makeup of what’s going through your pipe system. PVC and CPVC are resistant to many of the same chemicals, but some chemicals are better handled by PVC and others are better suited for CPVC. To be certain which material is right for your job, you can consult a chemical compatibility chart.