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Noise from PEX/PVC drain pipes

We are at the stage of starting the framing for the new construction home in Pittsburgh. It is also a Passive House duplex. Our architect specified cast iron for domestic water drainage pipes (from shower and toilet, etc.), mostly on the account that these result in most quiet interior. For delivery of the water within the house, PEX is planned. Then we heard that iron pipes are more susceptible to clogging. Is some compromise, where pipes close to dining/living room are cast iron, and PEX elsewhere an OK option?
At GBA, I did read on environmental life cycle comparison already between PEX and iron, lean towards PEX on this account, but would like to minimize these kind of noises. What would be recommended and what else should we consider..?

Asked by Lucyna de Barbaro
Posted Dec 6, 2014 7:43 PM ET
Edited Dec 7, 2014 6:31 AM ET


14 Answers

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Pex water lines don't make any noise, so you have no concerns there. I don't think cast iron pipe can be rationalized in a residential setting. It's heavy, expensive, and harder to seal than pvc. Secondly, there are many things in a house that will make more noise than your plumbing, but if you're worried about it, double up your drywall and insulate the wall where your main stack runs through.

Answered by Rick Van Handel
Posted Dec 6, 2014 9:05 PM ET


If the family is dining who is flushing? What your arch wants I would follow or change archs. They should know more than us and their customers or they why hire them?

PEX is fine, iron is fine, PVC is fine. The plumber needs to be involved.

Answered by aj builder, Upstate NY Zone 6a
Posted Dec 6, 2014 10:48 PM ET


Like Rick, I am confused by your references to PEX. I think that your concern about PEX noise is a red herring.

In case there is any confusion on this issue: PEX tubing is used for water supply pipes, not drainage. As long as there aren't any hot water lines that are pinched by small holes (a situation that can result in squeaking when hot water flows cause the line to expand slightly), the use of PEX tubing is not associated with noise complaints.

The other type of plastic you mention -- PVC -- is used for drain lines, not water supply pipes. If you have a PVC pipe connected to an upstairs toilet, and the PVC pipe is in a wall or ceiling near your living room or dining room, and if the cavity containing the pipe is poorly insulated, it is possible to hear water flowing when the toilet is flushed.

If this possibility worries you, you have several options. One is to insulate the cavity to reduce the noise. The other is to substitute a length of cast-iron pipe for the worrisome section of drain pipe; it is indeed true that cast-iron drains are quieter than PVC drains. Note that this approach does not require 100% of your drain lines to be made of cast-iron.

If the cast-iron pipes are properly sized, there is no need to worry about clogging.

Answered by Martin Holladay
Posted Dec 7, 2014 6:39 AM ET


Thanks for your explanations. Indeed, PEX is only for supply lines, so the questions should have been more properly formulated as the choice between PVC or cast iron. We will opt for the mixed solution: cast iron where the dinning/living rooms are impacted and PVC elsewhere. We will probably also try to insulate the areas around PVC. How much insulation would be effective? Like 1' on each side of the pipe? We will probably consider blown in fiberglass and some netting to limit its distribution.

Answered by Lucyna de Barbaro
Posted Dec 7, 2014 3:54 PM ET


Lucyna, Unfortunately blown fibreglass insulation is very poor at sound attenuation. You will get much better performance from foam wraps or mineral wool.

Answered by Malcolm Taylor
Posted Dec 7, 2014 5:55 PM ET


Or blown cellulose, as another insulation that would help with sound attenuation.

Answered by Charlie Sullivan
Posted Dec 8, 2014 9:53 AM ET


The long answer if we were talkng about PEX

Our entire house is plumbed with pex: 1" supply line; 3/4" lines to feed distribution and mixing manifolds; 1/2" for cold and hot water delivery to every fixture and heating radiator. These lines run through ceilings, utility chases and the walls, around corners in bundles and unbundled, buried in DP cellulose insulation on outside walls and open to the air in inside walls and chaseways.

Pex does have a relatively narrower inside diameter than copper or PVC for the same nominal pipe dimension. Pex fittings (i.e. elbows) are even narrower. Pex used for conventional plumbing and hydronic heating should not be subjected to anything that would make it "clog" nor lose its head by narrowing the inside diameter. Unless improperly installed and it develops a kink. To avoid kinks, bends must be supported with sleeves designed for that purpose. To increase flow (loss of head), upside the ID where nexessary (long runs for example) or use secondary monifold distribution points.

Pex is faster and cheaper to install than rigid pipe and pex compression fitting/joints are less likely to have a leak. Although compression fittings are common for copper installation now, making it much faster to install with more reliable joints than traditional solder. And good pex is expensive.

Pex does make noise. But so does copper. Its not the Pex itself that crackles and snaps, it is the friction noise when expanding pex rubs on pex, or on a metal or wood framing member, or when it passes through a barrier. That is when pex needs to be routed through suspension clamps, to stand off the Pex from any framing members, and be buffered to avoid pex to pex contact. Pex is particualrly easy and fast to install with wood I joits, double wall framing and larsen truss walls.

We used strips of geotechncial cloth (garden weed stopper fabric; driveway base fabric) to tie off, suspend and buffer the pex to pex and pex to wall contacts points. It works fine. No friction noise when kicking up the heat.

Pex for heating: Most houses are so well insulated and the heating systems uses outdoor reset with low temp supply that the small swings in temperature does not cause the degree of expansion or linear movement to make noise. The Pex itself does not crack and pop due to expansion.

Pex for hot and cold potable water: The only noise associated with this application is water rushing through pipes and copper is much noisier than pex.

If you are concerned aobut pressure drops due to the brass fittings, elows etc, then upsize the pex. ltive insdie diametrer fo p

Answered by flitch plate
Posted Dec 8, 2014 1:58 PM ET
Edited Dec 8, 2014 2:07 PM ET.


PVC vs iron pipes for DWV

This is current issue for me right now. PVC is tolerant to chemicals that will otherwise damage and eat away iron pipes. Do not use iron pipes for DWV (drain waste venting) if you have a furnace or air conditioning system that drains it condensate into the sewer though the house's DWV.

Condensate is the liquid effluent that contains carbonic acid. PVC and ABS DWV is not susceptible to this degradation and corrosion.


Answered by flitch plate
Posted Dec 8, 2014 2:06 PM ET
Edited Dec 8, 2014 2:40 PM ET.


While furnace condensate is corrosive, air conditioner condensate is not. Air conditioner condensate is simply distilled water.

Answered by Martin Holladay
Posted Dec 8, 2014 3:13 PM ET


Hey guys, was reading through this thread regarding pex water (supply) lines making noise as the hot water expands and contracts the plastic. Does anyone have a recommendation on how to cut down that noise? How much expansion does the pipe have? How much bigger does a hole through a stud need to be compared to the pipe?

Answered by Clay Whitenack
Posted Feb 17, 2017 9:01 AM ET


Size your holes (drilled through framing members) to be generous, so the PEX slides in easily, and don't worry. For more hints, see Comment #7 by Flitch Plate.

-- Martin Holladay

Answered by Martin Holladay
Posted Feb 17, 2017 9:39 AM ET


I was under the impression that the noise in drains can be significantly reduced by putting cast iron pipes in the VERTICAL sections of the drains. The rest of the drains can be PVC. Matt Risinger has a video blog on this topic as well.

Cast iron will last for a LONG time. And if it's in the vertical sections only, you won't have as much sediment. I don't think corrosion should be a design constraint in this case.

Answered by andrew c
Posted Feb 17, 2017 10:17 AM ET


Andrew. I tried the cast iron/PVC approach on my house and was disappointed in the amount of noise reduction it provided. If using that strategy, I suspect it helps to locate the line in an out-of-the-way place and to add insulation to further muffle of the sound.

Answered by Steve Knapp CZ 3A Georgia
Posted Feb 17, 2017 11:29 AM ET



You might enjoy the capability to gather some of the heat out of the hot water lost in your drain with a heat recovery unit such as a power pipe or similar product. just google "power pipe" to gather more data.

Now is the time to consider a product such as this. You could insulate around it for noise with would most likely help the efficiency of the unit even further.


Answered by Drew Baden
Posted Feb 17, 2017 12:00 PM ET

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