What is PVC?
PVC is a plumbing material made of a plastic called PolyVinyl Chloride. It is assembled by fitting and glueing sections of piping together in joints. It is most commonly used for drain systems, and sometimes used for water supply as well. Because it is not made of metal, PVC does not experience rusting and corrosion, such as galvanized and cast iron piping does.
Why is a hot water supply line in PVC a problem?
A weakness of PVC is it's resistance to heat and pressure, often just barely being high enough to support transporting heated water. To avoid this weakness, CPVC (Chlorinated PolyVinyl Chloride) is instead used for water supply lines. Where PVC is rated up to 140 degrees F, CPVC is rated up to 200 degrees F. While water in the home does not generally reach these temperatures, many years on transporting hot water approaching the limits of the material will deteriorate its temperature and pressure resistances. Because of this, using the much higher rater CPVC will keep your piping safely functional for many years to come.