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Pex Expansion Concern

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by McKraut, Apr 5, 2012.

  1. McKraut

    McKraut Member

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    I was reading the "Idronics, Journal of design innovation for hydronic professionals" by Caleffi. It has a formula for the linear expansion of PEX tubing based on both temperature change and length of tubing. According to the example they use, if you install a 100 feet run of Pex when it is 60 degrees, and it is warmed up to 190 degrees, the PEX will expand in length by 14.7 inches. Is this correct? I have not heard much concerning the expansion of PEX, so my assumption was it was not this significant. They recommend the usage of a flexible expansion compensator.
    Can anyone give me some input on this?

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  2. McKraut

    McKraut Member

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    Tennman,

    If you are around can you tell me if you had or have any problems with your install with respect to expansion of the PEX?
  3. StihlHead

    StihlHead Guest

    I never had any problems with that kind of expansion with the CB OWB that I installed, running from 50 degees F. up to near boiling (210 degrees F.). That system has 60 feet of one inch PEX (dual lines) running from the OWB to the house and about a 20 ft section between the hydronic floor Hx and the DHW Hx inside the house. Those lines were buried for 20 feet inside a corrugated drain pipe and foam insulation, another 10 feet inside the corrugated drain pipe running up a wall into the attic, and a loose 30 foot run in an attic. We also had about 12 PEX half inch zone heating lines in the hydronic floor heating system and they did not expand at all. They were connected to a brass manafold and there was never any flex in the lines from expansion that I saw.
  4. timberr

    timberr Member

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    I have over 100' of 1" PEX in my system it is all exposed in the basement and I have seen no evidence of such expansion. Most of the PEX is from Boiler to Storage and Storage to secondary loop.
  5. woodsmaster

    woodsmaster Minister of Fire

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    I have some runs of 1/2 inch pex in my crawl space. they do expand some. I installed them cold and gave myself a little extra. When they get hot you can see that they expand some. They droop a little inbetween the fasteners. I don't think I needed to leave the extra.
  6. McKraut

    McKraut Member

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    I guess the take away from this would be:

    that if you are buying PEX by the foot, it would be best to buy it on the coldest day of the year........
  7. infinitymike

    infinitymike Minister of Fire

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    I have been told that to help with expansion, to put a soft bend instead of a hard 90* fitting (if possible). I have 70' of 1"pex running from the Wood Boiler in the garage to the basement . It has 3 hard bends but near the connection to my primary loop it has a large soft bend. I've never seen a tremendous amount of expansion.
  8. heaterman

    heaterman Minister of Fire

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    Pex does grow significantly. The trick to dealing with it is to leave room for expansion/contraction.

    One customer had a 120 foot underground run of pex inside Thermoseal and it grew enough to pull his mounting bracket right off the wall in the basement.
    When you lay it in a trench outside make try to leave a few "s" curves in the trench. Don't pull it tight.

    The ration of expansion is the same regardless of diameter. Another customer who had 1/2" stapled tight to his subfloor, called to see what could be done about the noise. Everytime that zone kicked on and hot water hit the pex, it sounded like a herd of mice running through his house from all the tick tick tick going on.
  9. Tennman

    Tennman Minister of Fire

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    MK, been on vacation since wednesday. I just mentioned differential expansion and bond line shear over in the other pex insulation thread. I have about 170' between boiler room fittings and the heat exchanger. I'm certain that thermal expansion forces are greater than bond line forces. At the HX end I have about a 16-18' gentle curve hanging from the overhead. I have about 5-6' g gentle curve to the black iron manifold. Their coefficient of thermal expansion must be very conservative by a factor of 3-4. Ain't no way on my system I'm getting anywhere close to 24-25" if that was right. It's not noticeable in my system so I'm gonna guess 2-3" in 170 feet..... At most... Maybe. Heatermans done more systems so he can chime in but that expansion coefficient is way more than what I see. Happy Easter from the Volunteer state.
  10. McKraut

    McKraut Member

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    Ok. Thanks for the input guys. This is the kind of stuff I lay awake at night thinking about. I appreciate your expertise and experience. Tennman, I hope you had a good vacation and a happy Easter. It was a beautiful day here in PA.
  11. jpgarnva

    jpgarnva New Member

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    Tennman, That's what I was curious about in other thread in which you replied. If heaterman had a bracket break loose from a wall, is there the possibility that the pex could break the foam insulation? If it was a straight path the pex would have nowhere to go but up/down or side/side. Is this pressure greater than the tensile strength of the foam? That was why we opted for the microflex. Got to keep groundwater out period.
  12. Tennman

    Tennman Minister of Fire

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    Well... what do you know. McKraut. Just noticed South Central PA in your thingie. I was born in Altoona and I'll be coming up to visit my mom in a few months. But been away a very long time.

    JP, in the other post where I discuss differential thermal expansion I tongue in cheek give a clearance estimate when two surfaces lose their bond due to differential expansion. Basically what happens is you only loose the bond but the surfaces remain for all intents and purposes touching. So like I said in the other post the gap is so small water filling the void is really not an issue and if it did it would be several molecules thick so essentially irrelevant. Don't sweat the small stuff and this issue is so small..... fagiddaboudit. In my line of work I must deal with differential expansion regarding material selection all the time because we care about passing loads from one material to the other. But here we don't care about loads, just minimizing the transfer of energy. Cheers
  13. McKraut

    McKraut Member

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    Tennman,

    I live about 75 miles south of Altoona in Fulton County. These parts of PA are still beautiful. If you need a rest, stop by.
  14. McKraut

    McKraut Member

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    Tenman,

    This is an old thread, but I am getting ready to install my boiler and I was wondering (hoping) if you could take a picture of your "5-6' g gentle curve to the black iron manifold" and post it for me. If you could do this I would greatly appreciate it. I have an idea of what it would look like, but a picture is worth a thousand words.....

    Bob
  15. Tennman

    Tennman Minister of Fire

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    Well hey Bob. Gassifer started a thread a few weeks ago called "A few pics of your systems" that at this moment is on page 2. In there is my first successful upload of images of my system to Hearth (Taxi helped me in the past). My third system picture will show you exactly what you need. What you'll see is the final sweeping bend from 2' underground to attachment to my boiler room manifold. I used industrial grade plumbing mount channel and clamps. No indication of movement at the boiler end or that the final gentle radius changes at all. In my root cellar I have about 16-18' attached to the ceiling with gentle sweeping bends. I'm still astonished at the suggested coefficient of thermal expansion in the manual. Cheers!! U near Bedford county? Don't remember where Fulton is relative to Blair county.
  16. McKraut

    McKraut Member

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    Hi Tennman,

    That's what I wanted to see. I feel comfortable with the setup I was planning now that I see what you've got.
    I was ready looking at your post and noticed your EKO. Do you like it? Mine is still in my barn. I am building a timber-framed woodshed to store the boiler and I am a little behind. I built the shed bigger then I planned, and it is taking a helluva lot of time to get this done. I milled three poplars for the siding (I saw your woodshed was poplar too). I chose poplar because it is so straight grained. I was amazed at how bowed the boards came out. We milled about 1000 b.f. and I will barely have enough straight boards for siding to cover the shed. What a suprise. Anyway, I'm getting side tracked. Thanks for all your help. I appreciate it.
    Directly south of Blair County is Bedford County, and directly east of Bedford is Fulton County. Trust me, there isn't much going on in Fulton County and most people have no idea where we are.
  17. Tennman

    Tennman Minister of Fire

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    Glad it helps. I purchased a BioMass from New Horizons. It may look like a EKO, but it's Zenon's BioMass product. He incorporated his lessons learned as an EKO imported in the BioMass. Don't ask me how that works out as a distributor..... We have lots of poplar construction on our property. Poplar has a natural insecticide to inhibit termites (so I'm told) and it appears to be true by looking at what the bugs have attacked on our buildings. I've found it critical if the poplar is very green to keep it tightly stacked to get some drying or attach it immediately to the building to keep it true as it dries. But I love the wood. All the poplar lap siding on our house is over 160 years old and just beatiful. BTW, I've also been warned that breathing poplar dust is unhealthy! Google that. Now I know where you are and sorta know the area. I've been thru Breezewood hundreds of times!!
  18. McKraut

    McKraut Member

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    Tennman,

    I bought a BioMass 60 from Zenon. Was he helpful? I need help designing my system and I was going to ask him for help. Is it worth it?

    I had no idea poplar had natural insectcide in it. I used it for barn siding (and will for the shed too). I learn something new every time I check out this website. Thanks for the warning on the poplar dust. I must have inhaled a pound of the dust when I was cutting it. Maybe I'll bump up the life insurance.......

    Bob
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  19. Tennman

    Tennman Minister of Fire

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    Yes, Zenon is helpful. But it would have been difficult without the guys here. When you're ready I can email the Taco pump sizing spreadsheet I created from the TD10 datasheet. Whether you use a Taco or not, it will compute flow rates and gpm so you can make an educated choice. Then you run it by the experts here for the experience based sanity check. The two big decisions for me was validating my Hx sizing and the main circulation pump selection. If you're a DIYer, the guys here are invaluable.
  20. BoilerMan

    BoilerMan Minister of Fire

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    BTW, thanks Tennman, I spent almost an hour last night reading about poplar.......... I've got around a cord of it in the stacks for the 2013-2014 season too. Never thought anyone used it for exterior grade lumber I do, however, know several contractors who use it for interior trim because of it's workability.

    TS
  21. McKraut

    McKraut Member

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    Tennman,

    I will be contacting Zenon some time in the next few weeks. If you can send me the spreadsheet, that would be great. Do you want my email address? Thanks for everything....

    Bob
  22. McKraut

    McKraut Member

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    By the way, I just added an avatar to my profile. Isn't it beautiful?
  23. Tennman

    Tennman Minister of Fire

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    You can PM your email address or post here and I'll email. Download the Taco TD10 pdf document and use the parameters from the TD10 graphs. My system parameters will be a useful "go by". Yellow cells = inputs; Green = computed values. Pretty easy. Zenon's circ pump recommendation for me was way under the Taco recommendation for my conditions.
  24. McKraut

    McKraut Member

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    It's sweetairfarms@frontiernet.net
  25. McKraut

    McKraut Member

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    Tennman.....looking at your woodshed, how long ago did you build it? I like the natural coloring on the siding. Initially I was going to paint my shed, but I like the way your building looks. Also, I see that the shed isn't heated. Have you had any problems related to that?

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