You can think of CPVC as PVC’s cousin. They are similar in many ways, but they shouldn't be used interchangeably. Both are made of the same basic elements with one distinguishing factor. CPVC is altered by a free radical chlorination reaction that effectively increases the chlorine content of the material. This difference in makeup allows CPVC to withstand a wider range of temperatures. This is why many building codes require the use of CPVC as opposed to PVC for use in hot water applications. The ASTM standard allows PVC to be used in applications not exceeding 140 degrees F. Temperatures over this can cause softening of the material and weakening of joints. CPVC on the other hand can handle temperatures up to 200 degrees F.
There are a few other differences between the two materials. PVC has its own pipe sizing standard in North America called Nominal Pipe Size (NPS), while CPVC is available in either NPS standard sizing -OR- CTS (Copper Tube Size). The copper tube sizing system is an entirely different sizing system from Nominal Pipe Size, and as the name implies it is the same system used for copper pipe. Before purchasing CPVC be aware of what your use will be, and what sizing system you require. Color can be a clue, too. Often CTS CPVC is an off-white or yellowish color, while schedule 80 CPVC (NPS) is a light gray color. PVC pipe and fittings usually comes in white or dark gray. Always check the manufacturer printing on the pipe to be sure.
Because of the differences in chemical makeup, sometimes PVC or CPVC also require different primers and solvents. The creation of a strong joint depends on the cement’s ability to chemically soften the plastic. For this reason you should always use a cement specific to the material you are using.
