Pex tubing "grows"

[simonmeridew]

I installed an outdoor boiler this summer/fall and it works great. The only issue that I didn't plan on is that the 1" Pex tubing that I plumbed from the boiler to the heat exchanger is considerably longer than when I installed it. There's straight sections of hot and return that are about 40 feet long, and they seem to have "grown" about a foot since the water got hot inside. The boiler temp is running about 170 deg.
I'm thinking I need to reduce a section by maybe 9 inches, but I want to get the length right since I need to shut down the boiler and the tubing is full of water. I don't want to have to do it again.
Any suggestions? What's the expansion per foot or otherwise for this stuff?
simonmeridew

 

[dqdave1]

What is the temperature rating for the pex? 170 is pretty hot. You may begin to have problems if it expanded that much. Looked up pex; says it is rated to 180 f. It should be marked on tubing. I am going to guess that you need to allow for the expansion/contraction using a type of loopbefore the rigid connection.

 

[CurlyDave]

The thermal expansion of PEX is listed as 90 parts per million per degree F on this wwebsite Thermoplastics - Physical Properties .

If you installed the PEX on a 70 degree day and then ran it at 170 degrees, the temperature increase is 100 degrees and you would expect a length increase of 9000 parts per million or about 0.9%, roughly 1%.

For 40' of pipe this would be ~.4' or 5".

You are seeing roughly twice this, although I have a hard time understanding how one measures the length increase of a pipe connected to reasonably immovable objects at both ends.

Bottom line here is that if you disconnect the pipe and let it cool down, the thermal expansion will contract back, and you will find the pipe the right length. You are going to have a tough time shortening that pipe and then hooking it up.

As dqdave1 suggests, a pipe loop is the way to handle this. I would add about a 6' loop of pipe to both sides of the circuit. Since this is an outdoor application you need to be aware that PEX is subject to UV degradation if it is left exposed to sunlight. You need to protect the pipe from sunlight, either by burial or by covering it.

It is possible to protect some types of pipe by painting them, but I think paint would flake off of PEX.

A much better plan than a PEX pipe loop would be a loop made from the corrugated copper lines meant for hot water tank hookup. You might have to join several of them in series, but I expect a 3' diameter loop (~ 10' of corrugated hookup line) would work quite well.

 

[Egon]

On pipelines expansion loops are a pretty common thing.

 

[MarkV]

I would be a bit worried if PEX has a top rating of 180 and you are running 170 degrees through it. Does not sound like much of a safety margin for any variation it temp. If it were mine and were to give out it would for sure do it the coldest day of the year.

MarkV

 

[mohrds]

From the PPFA (Plastic Pipe & Fittings Association) website (ppfahome.org):

"PEX tubing can be used up to 200ｰ Fahrenheit for heating applications. For plumbing, PEX is limited to 180ｰ F. Temperature limitations are always noted on the print line of the PEX tubing.. PEX systems are tested to and can be used with standard T and P relief valves that operate at 210 F and 150 psi."

An expansion loop is a must on a long run. Also keep in mind that the expansion happens uniformly so the tube needs to be able to slide in whatever mounting it is in. For an outdoor use, no PEX pipe can be exposed to sunlight.

Doug

 

[jpm]

did you use the insulated 4" 1 piece tubing ? my run is over 70 feet with min
expansion but i did leave room at the ends for movment

 

[MileyPink]

Are they energy efficent for money?