Galvanized supply line question

esmith · Oct 16, 2013

We just demolished a 60 year old home and are building a new house. We found that the supply pipe from the city water supply is 1.5" galvanized. It looks to be in pretty good shape, but has some evidence of internal and external corrosion. It's about a 270' run to the meter near the street and about half of this is in an easement, but under the neighbor's extensively landscaped yard. Would it be possible to use this pipe as conduit and run a pex pipe inside it? Or do you have any other suggestions? Thanks, Ed

Jadnashua · Oct 16, 2013

The required size of the pipe and the distance it has to travel, plus how much water your house needs all go into deciding how big the pipe should be. If the pipe ends up too small, while the pressure will stay the same when nothings on, as you try to use more water than the pipe can handle, the flow can't keep up. Think soda straw verses fire hose...at a trickle, they're the same, but if you need it, you'll get LOTS more water out of the fire hose!

Without knowing what's going to be in the new house, it's hard to say what size you need. 1.5" supply pipe is bigger than an average house, but you may not be planning an average house. Are you measuring OD or ID? If OD, that could be much more common. IOW, need more info.

There are ways to minimize disruption to the landscaping depending on the soil, how deep the line needs to be and probably other factors. But, I doubt you can use it as a conduit for pex...it would end up being too small of a diameter for your needs.

Sponsor · 2022-01-29T12:20:58-0800

Craigpump · Oct 16, 2013

Dig a trench and put a new line in. Just because the pipe looks ok where you can see it doesn't mean it's good the entire run, nor does it mean you can slide another line through it. I have a piece in my shop that was thought to be good too until it was dug up. It looks like an 1.25 galvanized flute.

hj · Oct 16, 2013

The inside of the pipe SHOULD be so fouled with rust the you would not be able to run any adequate sized tubing through it.

u.s.coins · Oct 17, 2013

I wouldn't even try using any of the galvanized original. just inviting nightmares. jmo

esmith · Oct 19, 2013

Thanks for your replies. Here's a picture of a short section of the pipe.

It's about 1 9/16 id and 1 15/16 od (where it's not corroded.) Seems like schedule 40 size 1.5" to me. I could get a piece of 1" pex through this piece, but through 270' ???, especially if the corrosion varies as much as your experiences indicate. I don't know why the original pipe is this size. I know that they originally owned the entire acre and maybe it was irrigated with city water at some point in the last 60 years? It's currently irrigated from the river. The new house is not unusual. 3.5 bathrooms, kitchen, etc. 2 stories with a basement. Does a 1" pex line 270' long seem adequate. Static water pressure is pretty good down here. I'm only a half mile from the water treatment plant, same elevation. I haven't measured the static water pressure, but I'd guess it's 60-80 psi. My temp hydrant will about blow a short section of 5/8" garden hose out of your hand. Do you think I could ream the corrosion out the inside of the pipe with a sewer snake to allow more room to use it as conduit for a pex line? Thanks.

hj · Oct 19, 2013

Sewer snakes are no that long and do NOT remove rust from the pipes, unless you use a carbide cutter.

Jadnashua · Oct 19, 2013

The way the water supply pipe is sized requires knowing at least three things: distance, Water Supply Fixture Units (WSFU), and the water pressure. The goal on any supply is to still have adequate flow and pressure when you're using your water. Your town may have it's own charts to determine the supply line (and meter size), but this reference should give you a running start http://www.engineeringtoolbox.com/Water-Supply-Fixture-Units-d_1073.html and once you've added those up, go to here http://www.engineeringtoolbox.com/wfsu-pipe-lines-d_1075.html to get an idea on the pipe. Unfortunately, their charts only go up to a max of 200', but you can interpolate from the curves on the graphs and be fairly accurate, or search for some others.

1" pex, I don't think will cut it...note, the pipe sizes are based on (I think) copper nominal sizing, and 1" pex is closer to the flow capacity of 3/4" copper. Run the numbers, report back.

Dj2 · Oct 19, 2013

You are facing the inevitable - replacing the main line, the entire 270 feet.

esmith · Oct 22, 2013

I've come up with about 34 fixture units in the new house. Extrapolating from this graph it looks like I'd need an 1 1/4" line.

The 2nd order polynomial trendline looks like a pretty good fit to the available data, but its quite an extrapolation and seems kind of conservative. Anyone have any practical experience in this sort of situation?

hj · Oct 22, 2013

How many people you have in the house and how many of them could be using faucets simultaneously, (i.e. showers or bathtubs), is a better indication of "volume demand" than the WSFU, which is a theoretical number. you could have ten shower rooms, but if there are only two people living in the residence, the flow demand will be less than if there were 10 teen agers living there.

Terry · Oct 22, 2013

For that distance, a 3.5 bath home would require a 1.25" line.

1" PEX is more like a 3/4" line.

esmith · Oct 22, 2013

Would you recommend PEX or HDPE or gold (I mean copper)? There's only my wife, me and a 13 year old boy who likes long, hot showers in the house full time. I measured the static pressure and it looks like 68 psi.

Gary Swart · Oct 22, 2013

I concur with the other advising total line replacement. If you elect to go with copper, you should know that copper joints underground must be brazed, not soldered. Many people chose PVC to replace their old lines, others like copper. I can understand with the distance you have to cover, cost will be a consideration. Also with that distance, it would be wise to consider a professional. They could do the job and your neighbor's yard would left in good condition. You really don't have too much choice about putting in a new line, patching old galvanized is not very wise. Might get you by for awhile, but eventually it will develop leaks.

Craigpump · Oct 23, 2013

Poly would be the least expensive, plus I'm not sure how well PEX would hold up in a direct bury application.

Wet_Boots · Oct 26, 2013

Gary Swart said:
I concur with the other advising total line replacement. If you elect to go with copper, you should know that copper joints underground must be brazed, not soldered. Many people chose PVC to replace their old lines, others like copper. I can understand with the distance you have to cover, cost will be a consideration. Also with that distance, it would be wise to consider a professional. They could do the job and your neighbor's yard would left in good condition. You really don't have too much choice about putting in a new line, patching old galvanized is not very wise. Might get you by for awhile, but eventually it will develop leaks.

Would no mechanical joint be acceptable? I recall someone at a code official's office bewailing the given requirement that the 200-foot water supply to the house he was working on be one uninterrupted piece of copper, which he wasn't going to have an easy time obtaining. I suggested that a 200-foot length of poly be considered instead.

"I should use poly?!!" the guy exclaimed. I told him not really, but that it was code, and maybe the official would like the idea of rolls of copper connected with flare fittings a lot better than one uninterrupted segment of poly, so that the guy could have what he was looking for in the first place.

Terry · Oct 26, 2013

Copper can be soldered underground as long as it's not under concrete.
Joints under concrete are silver soldered. Brazed.

200 feet? Maybe poly or PVC as an option.

Wet_Boots · Oct 26, 2013

I know our muni purveyors decades back would've gagged on the idea of a non-mechanical joint on a supply line, especially since the supply lines were almost always upstream of the meters. Put the meter in a pit by the curb, and it was another story, since house-supply leaks weren't on their dime.

Galvanized supply line question

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