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Pex expansion challenge

Jamo Member Posts: 4
Hi folks, I'm doing an above floor installation using 3/4" plywood sleepers with stamped aluminum plates. I have a guy helping with the installation who doesn't believe the pex will expand if we hold it tightly enough in the plates (controlling the spacing of the sleepers so the plates are snug and the tubing presses in tightly after). I'm just concerned that the pex will want to expand somewhere, and if it can't expand laterally should I just leave a bit of space at the end of each run for the loop to stretch out lengthwise?

P.S. I'm using REGULAR pex. Not Pex-Al-pex... The system is running off a high eff condensing hot water tank with heat exchanger. I have no plans for an outdoor reset, although I could be convinced if it will make a big difference. The house is newly renovated with good insulation and vapour barrier, so heat loss should be minimal. The radiant floor heating is my primary heat source, so it will be fired up for the entire heating season (which, in Toronto, Canada can be up to 6 months).


  • SWEI
    SWEI Member Posts: 7,356
    outdoor reset

    will make a huge comfort improvement with radiant floor heating.  It will also minimize expansion noises.

    I would consider it a requirement.  I would also look carefully at the use of a hot water heater as your heat source.
  • heatpro02920
    heatpro02920 Member Posts: 991
    Is this a tight budget


    If you can spare the cost of something like a TT60 vs the HE hot water tank, you will not be sorry... and that comes with odr.... I don't normally recommend a system like you are describing, I would go the little extra and do it rite.... I had a friend of mine I helped with his radiant, I talked him into using some less expensive ebay manifolds and spending a little more on the boiler, he originally picked out some expensive caleffi manifolds but we found some ebay models that worked good for A LOT less, like 90% lol.... that coupled with a few extra bucks got him a boiler...
  • Jamo
    Jamo Member Posts: 4
    Already underway... need spacing advice

    Thanks for the comments on O.R. and the suggestion of switching to a boiler. I am on a tight budget, which is why I went with the condensing HE tank. I was advised a while back that with only 2 zones (600 sq. ft each zone) of radiant heating, I'd be able to satisfy both domestic HW and space heating needs. The HE tank is a 100,000 btu input capacity. I already have it on site and paying a rental fee for it... I believe I could upgrade to a boiler down the road if the system has difficulties (I'll check with the rental company on that one).

    In the meantime, I'm installing the sleepers etc and really looking for feedback on whether and how much room for expansion I need to provide for. I've read differing opinions so far on how much the pex can be expected to expand. If the plates are held tight by the sleepers, and everything is a tight fit, should I expect that the pipe will act as it does in concrete, ie- by expanding inwards instead of outwards?

    I have so far been laying out the sleepers so that at the end of each run there is about 1/4" extra room. In case you're having trouble visualizing this, the pipe is hugging a curved piece of plywood to make the 180 degree turn, but at the wall I have a spacer piece of plywood (to support future hardwood flooring) and there is 1/4" space between the curved loop and that spacer. My thought is that if the pipe can't expand within the plates along each horizontal run then maybe it will give itself a bit of expansion at the turns. I haven't tested this theory yet, so I'm putting it out to the community...
  • Gordy
    Gordy Member Posts: 9,546
    Coefficient of linear expansion

    Applies to all materials. What effects how much is temperature difference, and how quickly that difference is achieved.

    Your control strategy, and water temperature are the driving forces.

    In other words a low temp radiant panel say 100* average water temp won't expand as much as one with 120 AWT.

    Control with outdoor reset, and constant circulation planes the peaks, and valleys in AWT to better manage noise issues from expansion contraction because the temps are slowly warmed, and cooled verses a bang bang control strategy.

    To directly answer your question the slop in the returns will allow for movement, but the big question is noise which you will get with the control strategy you plan to use. Tick tick.
  • Jamo
    Jamo Member Posts: 4
    O.R. Possible with an HE water tank setup?

    Hi Gord, is it possible to add outdoor reset to a system such as I've described? The hot water tank is called Envirosense. I'm going to try to post a pic of its specs here.
  • SWEI
    SWEI Member Posts: 7,356
    adding outdoor reset

    A Taco iSeries-R valve is usually the least expensive route http://flopro.taco-hvac.com/products/index.html?category=188

    Be sure to use a brass or stainless pump on the tank side.

    Did you use barrier tubing?
  • Gordy
    Gordy Member Posts: 9,546

    Sewing said
  • Jamo
    Jamo Member Posts: 4
    Non-Barrier tubing because of low running temps

    I was told that with a HE modulating tank and no baseboards or rads to drive the heat up I didn't need the barrier tubing. Thanks for the tip about the Taco outdoor reset. I'll definitely look into that.

    One more question, if anyone has opinions on this -- over the aluminum playes and sleepers how effective would it be to put mesh and thinset, as a base layer under a floating floor (either laminate or engineered click flooring). I was thinking it would create a bit of mass to help steady out the heat transfer. I would have gone with an 1.5" slab in the first place if I was confident the floor could support the weight. I'm thinking if the thinset with mesh could be made solid enough to support the flooring, maybe it would also moderate out the heating highs and lows and prevent the accompanying noises as well.

    Any thoughts on this are very welcome, since I'm starting to get paranoid that my design is going to be a noisy, inefficient mess :(

    p.s. if peoplel are wondering why I bothered taking this on its because I'm creating a basement apartment and didnt want the bulkheads of a forced air system, so I dreamed up the radiant floor solution. Just trying now to mitigate the potential problems. I got my earlier advice (and materials) from an online supplier, but I'm learning to be skeptical of their advice and consult with those who have professional installation experience. Unfortunately I can't find any local installer who will come near the project since I already have all the materials (not enough margin for them I guess).
  • SWEI
    SWEI Member Posts: 7,356
    edited April 2013
    non-barrier tubing

    means you will also need a brass, bronze or stainless circulator on the system side.  Two expansion tanks.  A heat loss calculation.  And if not a real hydronic contractor, at least a competent designer or PE to guide your plumber.
  • knotgrumpy
    knotgrumpy Member Posts: 211

    Off topic by a bit, but I am curious.  You rent the hot water heater (or boiler)?  Is that a common practice in Canada?


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