Throwdown: Copper v. PEX

June 1, 2011 3:02 AM

In housing construction, is it a universal consensus that PEX is superior to copper piping in nearly all applications?

Recently, I've been talking to HVAC contractors in connection with transitioning my home heating system from fuel oil to the cleaner, greener propane. Contractors seem to fall on both sides of the fence: 1) Those that say that the lines connecting the propane boiler to the heating manifold need to be copper, rather than PEX. Because the water in these lines is a higher temperature than that running, say, through radiant heat coils, it will cause the PEX to expand, creating shifting, noise, and strain on the brass joints and equipment at either end. 2) The pro-PEX crowd. To them, PEX (if it's the higher-quality variety lined with materials other than aluminum), can be used for nearly all household applications, no matter what the temperature of water running through it. Expansion is less than copper, and durability is far better than copper, despite the fact that copper joints are soldered. Copper acquires a build-up of minerals on the interior walls in hard-water locations--a problem that PEX is largely free of. PEX has nearly supplanted copper in all residential and commercial applications . . . So run the arguments of the pro-PEX camp.

Which of these opinions is more universal in residential construction? Is there any truth to the notion that PEX is a bad idea in lines to the manifold due to strain and expansion? Also, is there a possibility that the pro-copper contractors may be pushing copper for financial reasons, i.e. because it is more expensive and requires more time to install and therefore adds to their bottom line?

posted by Gordion Knott to home & garden (13 answers total)

IANAContractor, but when we had our house replumbed and had a new forced hot water baseboard system put in, both the plumber and the heat guy had nothing but raves about PEX, both in terms of workability and durability. There's copper coming out onthe furnace for a few feet then pex right up to each heat register, where it switches back to copper for conductivity. The only problem we had was due to a joint freezing because extreme (-20F) cold and its location in relatively uninsulated spot in our 180 year old house. It would still have happened with copper, and would have been harder to repair.
posted by usonian at 4:22 AM on June 1, 2011

PEX fails. A lot. I work in forensic engineering and a lot of our business is in wet houses. Because of PEX failures. Improper installation is the number one cause, something that doesn't happen with copper. You know you have a leak in copper the instant the water is turned on. Copper piping only for me, thanks.
posted by sanka at 4:35 AM on June 1, 2011

Seems like the failures of PEX are in the fasteners, not the material itself. Which is sort of a good thing, since the nice thing about PEX is that there aren't nearly as many fasteners. As an avid This Old House watcher, I'm not terribly surprised. Some of the "new" and "easy" fastener systems look pretty hinky to me.

My favorite fasteneing system was the simplest: you'd put a second ring of PEX over the end of the PEX line, expand it with an expander, and then slip it over the barbed nipple. In seconds, the PEX would squeeze back down and clamp onto the nipple forever.

I did some copper repairs to some plumbing in a ~30 year old house. Granted, this was not the most well-built house in the world, but nonetheless, the copper piping is starting to get worn out. The joints are literally thinning away from the inside out. I drained about a gallon of little green flakes out of the water heater.

All of that said, I'd probably use the copper (or plain old iron) from the boiler to the manifold. I can imagine where a short run of wide-gauge PEX could be stressful on the joints. But that's based on mostly my imagination.
posted by gjc at 5:20 AM on June 1, 2011

I am an electrician, not a plumber or a HVAC guy.

My understanding is that PEX is cheaper and much easier to install, since it is flexible. Cheaper and easier - but I have never heard anyone say better. I can't image anyone seriously arguing that PEX is a better material. It seems obvious to me that copper is better.
posted by Flood at 5:21 AM on June 1, 2011

Do you know the water temp coming out of the boiler to the manifold? If it's within the range for PEX I can't see why you wouldn't use it. I'd rather put PEX in for the ease and cost.
posted by Frasermoo at 5:30 AM on June 1, 2011

Anecdotally, there's still quite a few plumbers from the older generation including my father [he's in his 60s, a licensed master plumber, exclusively does residential repair and rehabs] who dislike PEX. He installs copper exclusively unless the customer specifically demands. I've worked with him part-time for the 3 years.

He and the handful of plumbers that I've talked to that dislike PEX believe that PEX doesn't last as long as copper, can leave a plastic taste in the water, and believe that PEX isn't necessarily better, but just a big marketing push by some plumbing companies to sell the newest things. Also, our water comes froma great lake, so there's not as many problems with hard water problems either.


I honestly can't say if either one is more longer-lasting or better than the other or vouch for those claims; I can only count on one of my hands the numbers of times that I've installed PEX.

For what it's worth, I wondered how much PEX had really taken off, and asked the counterman at the local supply house a couple weeks ago, who told me their total sales are still still 60/40, in favor of copper.
posted by fizzix at 5:39 AM on June 1, 2011

My money's on PEX. As with all alternatives, it's economics. That doesn't mean cheapest, it means optimal over the period of interest.

PEX is inert. It doesn't erode. Copper isn't inert and it does erode/corrode.

For a retrofit, I'm not sure I'd add PEX in a completely copper house, but in new construction, I see no reason to use copper. (One must assume that the installer knows how to install either one properly. )

Ease of installation, lower number of connectors/connections, inert conduit, cheaper, no lead, no commodity pricing issues (buy any copper lately?), color coding, lifetime... PEX wins.
posted by FauxScot at 6:02 AM on June 1, 2011

When they plumbed our house (about four years ago) I asked if they were going to use PEX. The contractor said he was "not yet sold on PEX" and they used CPVC for the entire house. So with the exception of a few feet of copper at various fixtures, we're all CPVC. I'm sure I'll grow a second head in a few years from the plastic but I like not having to deal with copper.

We do use PEX in our heating system, going from the hot water storage tank to the air handlers. This is a ground source heat pump, a lower-temperature system than propane or oil, so we may not have the same temperature issues your contractor is worried about.

If it's just a matter of a couple feet at the boiler, I don't see any reason not to use copper. I don't think you'll find too many contractors who will do a whole house with it though.

We have PEX at a cottage we go to, which my brother-in-law installed to replace the aging copper, and I really prefer it. The only connections are at the beginning and end of the run and everything is on a neat manifold.

If I were to do it again I might insist on PEX. I prefer the CPVC to copper, and technically the joints are all permanent connections and will never leak, but there sure are a lot of bends an branches in our plumbing. I prefer the direct runs that PEX gives you. We might get hot water in our upstairs bathroom a bit more quickly.
posted by bondcliff at 6:16 AM on June 1, 2011

Actually, PEX has a higher coefficient of expansion than copper.

This isn't necessarily something to be concerned about, unless you're using copper joints, which have a low coefficient of expansion. (Coincidentally, copper and brass have almost the same coefficient. You'll still get the aforementioned shifting issues, although an experienced plumber should know how to install pipes to minimize that effect.)

The pipe expands a lot, the joint expands less, and all of the sudden, your tightly-clamped PEX tube isn't so tight anymore. Properly installed, I imagine that there are ways around this this issue, and that PEX's inherent flexibility makes the high expansion coefficient a moot point.

(I'm not a contractor. Just someone who's studied a bit of materials science.)
posted by schmod at 6:38 AM on June 1, 2011

To answer your basic question, copper is superior. PEX is cheaper and easier for the DIY'er to install. Health problems associated with PVC are still unknown although more information is coming out with regards to heated PVC.
posted by JJ86 at 7:07 AM on June 1, 2011

PEX is cheaper and easier for the DIY'er to install. Health problems associated with PVC are still unknown although more information is coming out with regards to heated PVC.

PEX is not the same as PVC.

We had our house replumbed with PEX about 4 years ago. We discovered during a bathroom remodel that the galvanized pipe from the 60's was very rotten. We discussed copper and PEX with several contractors and the county, and I did some research. I deal with environmental issues and risk for work and I felt confident that we were not putting something into our home that was going to create long term health issues for any of us.

The cost savings was substational - the copper would have more than doubled the cost, and taken much longer to install. Our 3bd/2ba house was replumbed in less than two days.
posted by Big_B at 10:25 AM on June 1, 2011

If I were to build a new house today, hands down PEX. More specifically, I would look into the aluminum- or other metal-lined PEX systems, specifically MultiCor or flexALPEX. The fastener systems and tubing are more durable.
posted by SpecialK at 10:54 AM on June 1, 2011

for hot water to run a boiler? either copper or galvinized steel (copper is far preferable) assuming the hot water is hotter than typical domestic hot water supplies (say 150 deg F or more). Otherwise PEX. It is cheaper, easier to install, and inert. It should last longer than copper and is so much easier to repair than copper. I am going to be replacing my galvinized steel lines under my house (100 year old victorian with an unfinished basement to work in thank god) with pex. I may even put in a home run hot water system. The lines in the wall are all copper and will be staying that way because they are fairly new and in good shape and plaster walls are not fun to repair. However every pipe I can reach is going to be pex all the way to the fixture if I can do it.

I will put the same caveat on this as anything else-you get what you pay for. Cheap joints, flux and fixtures on copper suck just as much as cheap stuff on PEX, Or cheap stuff on anything.
posted by bartonlong at 1:40 PM on June 1, 2011