PEX versus PE....

[mrcaptainbob]

I have an outside wood burner that has the existing underground using the white PEX. Was installed almost ten years ago. Apparently the insulation is compromised as the snow has been melting along that run. New is in order. The existing run is about a hundred feet, the proposed is about eighty. The line from the well pump is about 120 feet and uses PE. Both are 1" id. the PEX is maxed at about 195* at about 7psi. The PE is around 55* at 60psi. Would PE be just as viable a product to use for the wood burner-to-house use as PEX? I did a heat experiment a couple years ago with a thirty foot loop of heavy wall PE in line from the furnace. It was layed out in the sun during the summer months, and I added a layer of insulation to a portion of that PE. It was there for several months with no deterioration. So....is it a viable replacement for the more expensive PEX?

[Speedbump]

I"m not really sure what your trying to do, and I have never used Pex. As a matter of fact, I've never even seen pex. It must not be popular in my area.

I can tell you that unless they have cheapened Poly in the last 30 years, it is some of the toughest stuff you can put underground. The strongest back then was 160#, but I understand they now have it in 200# or a little higher. It's pretty much bury and forget. Unless you don't get it below the frost line.

[mrcaptainbob]

Pex/pe....

Actually I did two experiments. The first was with a section of the lower grade PE. It split along the seam like it had a zipper! And here I thought it was extruded. I also tried a section of the same stuff, just a higher grade. And I do believe it was the 160psi stuff with the much thicker wall. No evidence of deterioration. I plan to run a new line from the outside wood burner to the house. And of coarse encapsulate it with insulation. Only with better stuff than what was supplied and recommended the first time. The PEX is also pretty difficult to work with when dealing with the one inch stuff.

[HayZee518]

Pex

I never had any dealings with PEX at least not in my house. I've always gone with solder in copper and fittings. I did see a clip on the home and garden tv about PEX. You can fish the stuff into hollow wall spaces just like wire and cable thereby eliminating restrictions from elbows etc. But it is expensive. tighter bends are possible but you got to heat the run.

[pushkins]

PEX IMO is a great product, it is pretty cheap as well. Like mentioned it's very easy to use, best part is PEX seldom splits when it freezes it swells like a snake that's just eaten and then goes back down when it thaws. Disclaimer here : I have seen a split but it's on very short sections of frozen pipe (inches) but it is rare. I think Lazypup posted a picture on this forum someplace with a split short piece as well.

[LazyPup]

This is a fantastic question, although I must point out that it introduces a number of trick questions and it appears that everyone has already missed the mark.


Quote:"
I have an outside wood burner that has the existing underground using the white PEX. Was installed almost ten years ago. Apparently the insulation is compromised as the snow has been melting along that run. New is in order"

I take a slight exception to the phrase "new is in order". Based upon the evidence I agree that the insulation is now somehow compromised, probably from saturation of ground water, but there is nothing there that would indicate any problem with the pipe. In fact, it is theroetically estimated that in direct burial all varieties of plastic will last thousands of years, which explains why our landfills are filling up so fast.

No doubt, replacing the insulation is in order but the problem is, digging up an existing plastic pipe can be very labor intensive because it must be done by hand and you have to be careful you don't damage or cut the pipe with your shovel as you go. In the real world, rather than pay two or three laborers to hand dig the pipe, and hope they can acheive the task without cutting the pipe, it is much more cost effective to just abandon the existing pipe and use a trenching machine to dig a new trench and drop a in a new line. The later can usually be done in a couple hours rather than a couple days.

The next question is, if we replace the pipe should we use PE or PEX?
This is a trick question;
First of all, we must use a pipe that is rated suitbabe for the anticipated working pressure & temperature. PE pipe is actually manufactured under
a dozen or more ASTM standards, and while there is some PE pipe that might be suitable to this task, it is highly doubtful that a homeowner would know where to find it. The PE pipe typically sold in local hardware & big box home supply stores is manufactured to the SDR standard (size dimension ratio). If you look on the wall of the pipe you will see the size followed by the SDR rating. By example, it may read 1/2" SDR 11. That means the actual wall thickness of the pipe is 1/2" divided by 11 or .500 divided by 11 = 0.045" thick. Also note that it is rated for 73degF. It may have a derated pressure rating up to 140degF however for hydronic heating we want to transfer as much heat as possible so they commonly run at 180 to 190degF on the supply run.

PEX tubing is manufactured under ASTM standards F-876 & F-877 and it is rated for both hot & cold potable water & heat transfer. Pex is rated for up to 200degF.

It should also be noted that per code, PE pipe is suitable for direct burial but it may not be used inside a structure.

IMO PEX would be the best choice for pipe.

Now let us consider the insulation. You lines were just installed a mere 12yrs ago and plastic pipe is anticipated to last for thousands of years. Its a crying shame that you have to rework this line because the insulation failed, and we certainly do not want to install the line in such a manner that you will be confronted with the same problem in another 10 or 12 yrs. Tecnically speaking, the material that they use to make insulation has very little insulation value. The true insulation is a result of the air that is trapped inside the insulation material, and if that trapped air happens to be displaced by water, you no longer have any appreciable insulation value. It then stands that to get the maximum efficiency out of the insulation we have to protect the insulation from water. Fortunately there is a very inexpensive method of doing that.

Per ASTM specification, PEX tubing cannot be exposed to UV light, even for a short time. By example, during installation if must be kept tightly closed in a box until the actual installation is being done and when PEX is installed through a joist bay where it may be exposed to even reflected sunlight through a basement window code requires the PEX to be covered with a sleeve or the underside of the joist bay covered with 6mil poly sheeting or other light proof method. As a result, they now make 100ft rolls of 6mil poly tubing up to ten inches in diameter. You could begin by covering your pipe with the standard peel & stick foam insulation, then pull a poly sleeve over the entire length of the pipe that will be below grade. The poly sleeve will prevent any water from entering into the insulation.

When I was living in Ohio I met some Amish men who owned a company making and installing the external wood fired hydronic furnaces such as yours and they showed me a fantastic method they use. First they install PVC schedule 10 poly pipe ( poly electrical conduit) with long radius elbows from vertical to horizontal from the burner to the house, then they insulate the PEX and pull it through the conduit in the same manner as one would pull electrical cables. The advantage here is that the PVC prevents water from getting in and if they ever have a problem with the line in future they can easily disconnect it at both ends and pull it out for repair or replacement, then pull it rigth back in place.

[mrcaptainbob]

Pex/pe

Yes, LazyPup, you're pretty close to being 100% correct. The water intrusion came about from those darned plastic compression fittings. They leaked and followed the PEX down inside the heavy vinyl sleeve. No way to get it out now. Although I did install the yellow caution tape above that PEX run, and again above the electric run about a foot above that, there's no justification to dig the old trench. A new one is easier and far better. Hand digging will be required at the house entry point, as well as at the stove end. The original PEX installation exists only in the ground and enters the house about six inches and transfers to 1" copper from that point on. No sunlight issues.
Back to the PEX versus PE question. The PE I tested a couple years had a rating of over two hundred degrees and a pressure rating that was far higher than the planned use. The stove temps range from <100*'s to 197*'s. The pressure is about 7 (seven) psi. Using the higher gauge PE I think will work out well for this application.