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Hot water in PVC?

Posted by markf (My Page) on
Tue, Feb 7, 06 at 21:04

I may have a problem. I'm redoing my backyard with a built in sink at the BBQ area and I ran two lines of standard white PVC to branch hot/cold from the kitchen. I recently read that hot water should "never" be run in PVC. The foundation for the BBQ area has already been poured... damn it. Is this true/ are there any options at this point? Thanks.


Follow-Up Postings:

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RE: Hot water in PVC?

PVC is not permitted for any potable water distribution within a structure but it is approved for use outdoors. The probability of having a problem is small, but the good side is tht if it does develope a leak it is outdoors where it will not cause any serious property damage.


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RE: Hot water in PVC?

that is correct, no hot water thru PVC. or as also indicated by lazypup.


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RE: Hot water in PVC?

OK. But, why?

Pinoke


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RE: Hot water in PVC?

CODE, which is flag that Pinoke does not salute. PVC softens with heat. It may not fail immediately when used with hot water, but gradually will bulge like an aneurysm and will eventually burst. This partcular code requirement has a technical basis.


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RE: Hot water in PVC?

That was my question. Good answer. Especially, if it is true.

Pinoke


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RE: Hot water in PVC?

Aloha Mark,

You can get several years worth out of the PVC before it starts leaking, but it will eventually start leaking if you run hot water in it. Even with cold water, PVC will get brittle and be fragile eventually. I've seen it used extensively for outside water piping, but I don't know the frequency of leaks. Some hillside neighborhoods over on the Kona side have dozens if not hundreds of long runs of PVC pipes on the surface of the ground going up to the water meters by the side of the highway. It would seem one erratic driver could cause a world of hurt to their plumbing, but so far I haven't heard that it has happened.

At this point, with the concrete in place, it looks like your options are:
1. leave it there and expect to fix it in several years when or hopefully "if" it leaks.
2. Dig up the concrete where the water pipes are and replace them.
3. Run new piping around the edge of the concrete.

You could do option 1 followed by option 3.


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RE: Hot water in PVC?

you could try feeding some soft copper through the hot water PVC line


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RE: Hot water in PVC?

Thanks guys. It seems like I'd be rolling the dice on a busted pipe somewhere down the road. I just found another option that might solve the problem: an under the sink water heater. I already ran power to the area, so maybe this is the way to go.


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RE: Hot water in PVC?

I have been in the Plumbing trade for nearly 4 decades and throughout that time every time I noted a change to the codes I made it a personal point to find out the underlying reasoning for the changes. To date I have yet to find any change that does not make perfect sense once you find out what prompted the change.

In the case of PVC, when it was first introduced into the plumbing trade in the mid 60's it was approved for all potable water systems, both supply and distribution. At that time it was also a common practice to operate water heaters at or near 180degF.

It was soon discovered that PVC will exhibit wall softening and glue joint failures at temperatures approaching 150degF, which explains why the ASTM standard for PVC now limits it to applications not exceeding 140degF. )

The PVC formula was then improved upon to create CPVC which can withstand temps up to 190DegF for a short time.

Initially the codes were ammended permitting PVC in the cold water service, but requiring CPVC in all "Hot Water" applications, however this lead to a lot of confusion amongst the general public and it was soon discovered that homeowners and DIY'ers were erroneously using the PVC in applications that required CPVC. It must also be noted that initially CPVC was made in the same white color and to the same Sched.40 dimensional specifications as was the PVC which then lead to a lot of confusion by mixing both the pipe and fittings. CPVC is still made to sched.40 specs and the only method of distinguishing the two materials is to actually read the labelling printed on the pipe wall.

The CPVC that is commonly used for distribution piping today is not made to ASTM pipe Schedule standards, but rather it is CPVC-CTS,(Copper Tube Standard) which explains the difference in overall tube dimension.

In order to further enhance the differences between the materials the ASTM introduced a color coding system for plastic piping.

ABS pipe is made in Black.
PVC pipe is made in White, Gray, (rarely in blue) and Clear. The gray color is primarily only used for shed.20 and sched.40 dimension and is primarily intended to be used as electrical conduit. PVC clear pipe & fittings is used in commercial and industrial applications that were formerly constructed of Glass pipe, and limited to applications not exceeding 140degF working temps.

There is a variation of PVC pipe that is made to ASTM "SDR" (Size Dimension Ratio)standard and may only be used for sanitary and storm sewer applications outside of a structure. (SDR, Size dimension Ratio is a standard that was originally used to define the thickness of concrete sewer pipe walls. Under the SDR standard the average thickness of the pipe wall is determined by dividing the pipe diameter by the SDR reference number. By example, a 4" PVC SDR-35 pipe would have a wall thickness equal to 4"/35= 0.114".

The codes specifically state that all PVC piping used to make the DWV (Drain, waste & Vent) system within a structure MUST BE schedule 40. ( You may not use SDR pipe within a structure)

CPVC is made in white and the creme color that we most often see in the local hardwares, big box stores or plumbing supply houses. In addition to the CTS standard it is also made in sched.40, sched.80, sched.100, sched.120 and rarely in sched.180


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RE: Hot water in PVC?

Wow. Thanks for all that info. How hot is typical "hot" water these days?


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RE: Hot water in PVC?

markf - similar to the soft copper suggestion above, if your PVC is a large enough ID, you might be able to pull some PEX plastic tubing through it and get around your problem that way.


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RE: Hot water in PVC?

LazyPup, that was just great. Thanks, so much!

Pinoke


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RE: Hot water in PVC?

Thanks. I will check out the copper and PEX options, but I have 2 buried 90degree bends that will make things tough.


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RE: Hot water in PVC?

So if I understand lazypup correctly, PVC pipe for interior cold water is against code because installers were confusing it with CPVC and using it for hot water lines. It that right?

David


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RE: Hot water in PVC?

MarkF..

My concern would be heat loss in an underground run of hot water piping.

Currently the Plumbing codes limit the maximum temperature of the hot water system to 140degF, however the maximum input temperature to a tub, shower or tub/shower mixer may not exceed 120degF unless the tub or shower is equipped with an anti-scald/pressure balancing mixer. In order to meet these code standards most residential water heaters are set to 120degF.

I would anticipate that the hot water demand at your outdoor barbecue location would be very small and only occassional use, therefore it would be much more practical and fuel efficient to install a small point of use tankless at the demand location. In this manner all you would need is one coldwater supply line to the barbecue area.

"Posted by: dnlblank (My Page) on Fri, Apr 14, 06 at 7:40

So if I understand lazypup correctly, PVC pipe for interior cold water is against code because installers were confusing it with CPVC and using it for hot water lines. It that right? "

Fundamentally you are correct, however there are a number of other factors that make PVC unsuitable for distribution piping.

1. As is common to all synthetic pipe, PVC deteriorates from exposure to Ultra-violet light

2. PVC has a very high co-efficient of thermal expansion and when used above grade where ambient temperatures can vary greatly it requires careful placement of hangers and supports to permit movement of the pipe. If the pipe if firmly held in place it tends to bend the pipe when it expands or in many cases the expansion will push the pipe through a tight hanger but when the pipe later cools and contracts it places a pulling stress on the joints which lead to premature joint failures.

3.PVC rapidly becomes brittle with age and must be suitably protected against mechanical shock that could break the pipe.

4. As the working temperature of PVC pipe increases it increases offgassing of the chemicals in the pipe which then go into the water.


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RE: Hot water in PVC?

I am planing on buying brand new home in NJ,and builder have use some type of red color for hot water and gray color for cold water thruout the house for hot water baseboard heat and all bathrooms,it is safer or better than copper?, what should i do?
any help will greatly appreciated.
thank you
mike


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RE: Hot water in PVC?

Not to mention or if it was, PVC can taint the water....

MarkF, not to rub it in or anything, but obviously you did some planning ahead, but didn't the fact the fittings etc you'd likely be using, are not made for PVC sizes? I would have thought that would have rung alarm bells.

On the upside, if you can persuade thin copper or pex through there, the pvc will act as insulation.

Do you plan to put pavers or tile on the concrete? If so, you could rent a concrete saw and just put a little trench for the real pipes in there.

Incidentally, longevity-wise, for embedding in concrete, copper is usually specified as it's the most durable.

One other question, what provision have you made for drainage?


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