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PEX pipe ISD and flow problems


Scottpat
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I'm curious if anyone has noticed flow problems with homes that have PEX pipe? At a chapter meeting several months back we had a speaker who was the head engineer at a local water municipality speaking on water flow at homes. He brought up the fact that if PEX pipe is marked 3/4" that its inside diameter is just a little over 1/2". Then to complicate things the copper fittings must fit inside of the pipe and that reduces the size of the pipe even more.

I had a new construction house last week that had a 3/4" PEX main line and 1/2" PEX throughout the house. Static water pressure at the house was 68lbs. Open up a fixture in the kitchen and a bathroom and the pressure dropped to 27 lbs. On the second floor the water pressure was not even enough to supply the shower. So if we subtract 1/2 lb per every foot of rise, that would mean that we had around 15 lbs of pressure at the second floor.

I really just started to notice this over the past couple of months, I'm curious if anyone else is seeing it as well.

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Originally posted by Scottpat

I'm curious if anyone has noticed flow problems with homes that have PEX pipe?

I see lot's of PEX installations. It's become the standard here in new construction. I haven't noticed any problems with flow.

At a chapter meeting several months back we had a speaker who was the head engineer at a local water municipality speaking on water flow at homes. He brought up the fact that if PEX pipe is marked 3/4" that its inside diameter is just a little over 1/2". Then to complicate things the copper fittings must fit inside of the pipe and that reduces the size of the pipe even more.

3/4" copper = .785" I.D.

3/4" PEX = .671" I.D.

I believe that, when new, copper has lower losses due to friction but as it ages, the losses increase and give PEX the edge. I'm not certain about that and I have no data to back up the claim.

I had a new construction house last week that had a 3/4" PEX main line and 1/2" PEX throughout the house. Static water pressure at the house was 68lbs. Open up a fixture in the kitchen and a bathroom and the pressure dropped to 27 lbs. On the second floor the water pressure was not even enough to supply the shower. So if we subtract 1/2 lb per every foot of rise, that would mean that we had around 15 lbs of pressure at the second floor.

Something's wrong there and it isn't just the fact that the house is plumbed with PEX. It sounds like there's a kink in a line somwhere.

I really just started to notice this over the past couple of months, I'm curious if anyone else is seeing it as well.

No. Flow seems to be fine with PEX.

- Jim Katen, Oregon

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I have had several clients report about this issue over the past few years. These clients are folks that have had their house re-plumbed, so they are comparing prior water volumes with post-repipe volumes. The only thing that changes in these homes is the distribution piping, and now the showers are sensitive to other fixtures running, potential scalding, etc, when they did not exhibit this characteristic previously.

While a new house might be fine, there is no one to compare the before and after effects. Just because something "is the standard in new construction" doesn't make it immune to problems.

Dom.

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I agree,

I never said that just because the houses were plumbed with PEX that they were immune to problems. However, the kinds of things that you've pointed out - showers sensitive to other fixtures running, potential scalding, etc., has nothing to do with the pipe; it's related to the types of mixing valves and how well they're installed and balanced. You can have those same problems in a brand new home that's fully plumbed with copper, PEX has nothing to do with it, other than the fact that whoever plumbed it wasn't paying attention to the way the home was going to be used.

OT - OF!!!

M.

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Originally posted by hausdok

I agree,

However, the kinds of things that you've pointed out - showers sensitive to other fixtures running, potential scalding, etc., has nothing to do with the pipe; it's related to the types of mixing valves and how well they're installed and balanced.

M.

If a house has no unbalanced issues for 12-15 years with copper and the valves don't change, only the piping changes, & the owners don't change their habits, yet notice the flow irregularities immediately... well, draw your own conclusions. No modern mixing valves involved anyway, just simple on/off, old -school style.

Different clients telling the same stories, and keep in mind Florida has an scourge of re-piped homes.

Dom.

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Which is my point,

The valves have to be designed or adjusted for the flows that the pipe provides. You can't go from 1/2 or 3/4 inch pipe to a reduced diameter and expect to get the same performance unless you either use a valve designed for those kinds of flow rates or you adjust (if they're adjustble) what's there. It's not like simply walking into the big box store, grabbing any old thing off the shelf and slapping it in; it kind of helps to at least read the instructions or hire someone who knows what they're doing.

OT - OF!!!

M.

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Wouldn't there be variables, i.e., what if there were 1" laterals, 3/4" risers, or otherwise "big" pipe, and it was replaced w/ 1/2" PEX, or there was some other rerouting of home runs, etc., etc.?

If all things were equal, there's not going to be any difference. If things are very different (radically altered pipe scheme), that by itself could be the difference.

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Haven't heard of these pressure issues with PEX. Pretty standard in PA.

However, I have seen documentation about chemical leaching with regards to new PEX installations. As water is flushed through a new install, some of the chemicals in the material itself, are known to leach out and after a short time, the risk diminishes.

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I had a pex house the other day (1 year warranty inspection) that had good static pressure of 60psi but with poor flow at the kitchen and bathrooms. All of the aerators on the faucets were clogged with a "whitish" film. There was plenty of flow with the aerators not installed. I am wondering if this is something consistent with what Matthew is talking about?

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Hi Charlie:

The whitish film you mention on the aerators would make me think of calcium and magnesium. The sort of stuff that a water softener should help remove from the water supply. You tend to also see clogged shower heads from the same problem.

The chemical leaching issue relating to new PEX installs, I don't believe, had to do with residue accumulating on fixtures or aerators.

Matt

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