PVC Pipe Size

[Davej]

So why is PVC pipe always larger than the marked size? The marked size isn't the ID or the OD.

[fiveoclocksomewhere]

The marked size is the ID. The OD depends on the wall thickness of the pipe. Hpwever, the ID size is not always exact. (Dont ask me why). This is fairly close for steel, copper and PVC/CPVC pipes. PEX is in a world of it's own and not even close to the listed size. Plus PEX fittings are greatly smaller than the pipe size, which is a restriction for water pressure. So I dont know how they can honestly rate that stuff.

Just recently I had to replace some old steel pipes. Someone had already replaced the section from the water meter to the center of the house with 3/4" PVC. I know that PVC is not intended for hot water. Only cold water and is most used for sprinkler systems these days. I did the rest of the house with CPVC, which IS for hot water as well as cold. I have only used CPVC for fresh water supply pipes, so I did not know that the

3/4" PVC was considerably thicker on the OD than the CPVC. But the plumbing store had an adapter for about $1.50, so it was no big deal to adapt it. But that PVC is probably 3/16" thicker than the same size CPVC.

If you buy the larger sizes for drainage, you run into more issues with wall thickness differences. Schedule 40 is usually used in basements and walls in a house. But there is a sewer pipe that is used underground, and that's a pale green color. (I dont know what schedule that is called). I had to connect the sch40 to that green stuff once and found that an adapter was needed there too.

When it comes to plumbing, there are no steadfast rules. Even flexible copper pipe (in rolls), is not the exact same size as the solid copper pipes. But as a rule of thumb, the ID is the listed size (or somewhere close to it).

[Dean Hoffman]

Doesn't PVC plumbing mimic PVC electrical? The OD is always the same. It has to be for the couplers, end fittings, etc. to be interchangeable between schedule 40 and 80. The production equipment for either electrical or plumbing could be the same if everything thing else is the same except the coloring of the components.

[gfretwell]

You have that backward. The OD is always the same for a particular pipe size with the exception of DWV and the size is really "Nominal". The classes of pipe sizes are Schedule 40/80 conduits, gas and water pipe, galvanized or PVC are the same size. Copper and CPVC share the same nominal OD DWV pipe share the same ID with schedule 40 so the OD is smaller. In the case of flexible copper you have "pipe" and "tubing". Pipe will be the same as rigid pipe, Tubing is measured by OD.