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Plumbing Bathrooms

Old Pipes, New Pipes

5 years ago

My apartment building was built in the 1950's. In the attached picture you see my new 1/2 inch copper pipe going into my shower valve. It has a circumference of approximately 2 inches. You also see the feeder pipe it is connected to. That pipe, (which I assume is steel?) measures approximately 3 inches in circumference. (I had to measure with a string with one hand in the wall so I could not be exact.)

Photo: https://www.dropbox.com/s/zp067q9m9tscyb9/IMG_0980.JPG?dl=0

According to this chart, It says that IPS at 1/2 should have a circumference of 2.6 and that 3/4 should have 3.3. Interestingly someone from my building said he thought our feeder pipes were 5/8 which the plumber said is not a thing. But perhaps with a 3inch circumference, right in between what 1/2 and 3/4 should be, that is what they are.

https://www.plumbingsupply.com/info-pipesizes.html

Is it safe to assume both pipes are close enough to 1/2 inch so there should be no reduction in pressure or flow from my old pipes to my new ones?

Featured Answer

Jake The Wonderdog

5 years ago

Looking at your photo it looks like the pipe to the right pointing up is 1//2".

Given that, It appears that the tee is a 3/4 x 1/2 x 3/4 and the new copper is 3/4... but it can be hard to tell from a photo without any reference.

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Comments (7)

Jake The Wonderdog
5 years ago
last modified: 5 years ago
Your pipes are 1/2" or they are 3/4". Your plumber is correct - 5/8" isn't a thing. BTW: Your plumbing isn't that old... I regularly worked with plumbing from 1900-1920's, even then it was pretty standardized stuff.

When we say 1/2" or 3/4" we are talking about nominal trade sizes. The OD and ID will vary based on if it is galvanized steel, copper, PEX, CPVC, etc.

And God bless your plumber for not beating you with a pipe wrench by now... I don't know that I would have exhibited so much self control.

Here's a tip: Stop obsessing over your GPM to your tub. Seriously. You are making everyone crazy - including yourself.

There are times when I say to the person posting, "if you think there's a problem, there's usually a very good reason you think that."

This is not one of those times.

Rather I suspect you have become the remolding equivalent of a Bridezilla.
Adam Gerson
Original Author
5 years ago
last modified: 5 years ago
Fair point. But I would like to know for my own curiosity, what size pipe is the old feeder given its 3inch circumference? 1/2 or 3/4?
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Bruce in Northern Virginia
5 years ago
Galvanized water supply pipe for a house is almost always 1/2" or 3/4", so my guess is that its 1/2". In my area the main water supply pipe is 3/4", and the supply to each fixture is usually 1/2". With the newer plumbing fixtures its probably a moot point, since they all have restrictors to limit the flow, and using a feed larger than 1/2" would not make them flow more water. Even my outside hose bib only uses a 1/2" supply, but IIRC it does not have a restrictor.

Bruce
geoffrey_b
5 years ago
I'll add: Copper pipe can be specified OD or ID. To convert ID to OD add 1/8". So 1/2" ID (Nominal) copper is 5/8" OD. Usually 3/4" is used for the main line, then 1/2" to the fixtures.

Galvanized pipe - go out to the hardware store and ask them to show you the pipe nipples - there you can compare 1/2" and 3/4".
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Debbi Washburn
5 years ago
What you are measuring i the outside of the pipes. The outside of a galvanized pipe will be larger than the outside of a copper pipe... These both look like 1/2" pipes to me. On a side note - I redid the plumbing in my small house - the main feed is only 1/2 " but everything else was done in 3/4 and my pressure is exactly the same as my neighbor ( community well )... so it didn't make any difference in the pressure...

Good luck with your project!
sofaspud
5 years ago
circle circumference = diameter * pi. So a 3" circumference means a diameter of .95" (OD) . Admittedly your string measurement is not exact.

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