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Frozen PEX in a slab?

johnnyd | Posted in Energy, Heating & Insulation on January 6, 2004 05:45am

Noticed last night that one of three 250 loops of PEX (WIRSBO) tubing in my workshop/garage slab registers ZERO GPM. The other two are normal. Outside temperatures have been around zero F since Sunday night, with a stiff NW wind.  This is the first heating season for this system, which was installed late fall 2003.

Slab sensor calls for heat at 55, keeps air temperature at ~ 48.  4″ thick slab is perimeter insulated with 4″ rigid down about 20″, 2″ rigid underneath, 1/2″ PEX is stapled to the insulation, re-rod laid over.  30 X40 ‘ Building is well sealed and insulated R38 ceiling, R25 walls, one window, two insulated garage doors. Shares one long wall with a heated bedroom/bathroom over a crawl space that also stays at 48 – 52 air temp. 

50 gallon propane water heater supplies the heat.  Water goes in at 100 degrees, comes out at 80 degrees.  Pressure at 12#s rises to 15 #s when heat cycle is on. Running just plain water- no glycol, as I plan to keep the thing heated all winter Don’t know how long or how often the pump runs as I have a day job and weekends are spent working on the new house nearby…but every time I go in there, at least once a day (except a few Sundays, including the 4th of Jan.) it’s a comfortable 48 to 52 degrees in there, and I easily brought the air temp up to 65 for a Christmas Day get together in the shop/garage.  Does seem to only run maybe one or twice a day.

Initially I thought the loop had become clogged with scale from the 5 year old HWH, but since this loop is the one on the most exposed part of the building, I’m starting to think that with so much time between heating cycles, that one loop could have frozen.  Seems unlikely, as the other two loops are registering about 1 GPM.  Slab on the clogged loop side is cooler than the rest, but I don’t think even near 32.

If it IS frozen, I’m hoping it will thaw with no damage.  I bumped the slab temp up to 60 this morning, pump came on, HWH lit up, it was pumping 100/80 within few minutes…but still only through the two good loops.

Anyone had a frozen PEX slab experience? How did it come out?  Should I shut this loop down?  If and when it thaws, will it spring a leak?

 

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Replies

  1. User avater
    CloudHidden | Jan 06, 2004 07:04pm | #1

    Could it have an air lock? Can you purge the system or the loop? Open both ends of that loop and run more water into it or even blow it out with an air hose?

    1. User avater
      johnnyd | Jan 06, 2004 09:24pm | #7

      I'll try that if it gets stubborn.  Thanks

  2. bearmon | Jan 06, 2004 07:06pm | #2

    Was working on a large outdoor paver project with tubing in the sand under the pavers.  Weather changed before it was complete and one loop froze. 

    Plumber fished a smaller tube into the PEX inside at the manifold and pushed it until it stopped, then pumped hot water at it.  Makes a mess, because it comes back at you, but it worked.  They kept feeding the smaller tube as the blockage melted until it was clear. 

    Bear

  3. joeh | Jan 06, 2004 07:49pm | #3

    How about upping the temp for a few days and see if you can heat the slab to the point of thawing the line?

    Maybe cover the slab with whatever is laying around? Like a big pile of 4x8 sheets of foam would be nice, but anything might help to retain some heat in the slab.

    I think the PEX will be okay, that stuff is tough. My unfortunate experiences with frozen PEX is whatever is on the end will suffer. Terminal stress test.

    Joe H

    1. User avater
      johnnyd | Jan 06, 2004 08:18pm | #4

      That's what I think I will do.  Just happen to have some foam around.

      Have time to provide any more detail on the "Terminal stress test."?

      What bolted me out of bed this morning was the thought that the frozen loop would thaw, spring a leak, slowly drain the system, the pump would keep running because the sensor would keep calling for heat, pressure would drop, pump would cavitate till it overheated and locked up, HWH would keep firing, things would blow and catch fire.

      1. joeh | Jan 06, 2004 08:36pm | #5

        Terminal stress in my first case was the kitchen faucet was closed when the pipes froze. Real bad for faucet housing, PEX was fine.

        Second time, the fitting on the end of the PEX split. PEX no problem.

        Third time, same thing, the fitting broke and the PEX was ok.

        I have a system that doesn't drain, but the first time was just that I was not expecting to be gone so hadn't drained the lines.

        Joe H

        1. User avater
          johnnyd | Jan 06, 2004 08:57pm | #6

          Thanks, I think I'll be OK then, as the whole building is FAR from freezing up..the two loops seem to do a fine job of keeping more than 2/3 of the slab warm, and air temp should remain about 55 or so, as I bumped the slab temp up to 60 this morning. 

          IF this one loop is even frozen anywhere, it's got to be a short section buried somwhere in the slab on the cold side of the building.

  4. User avater
    johnnyd | Jan 07, 2004 05:32pm | #8

    I'm convinced now that the loop is indeed frozen in at least a few places.  The loop in question is on the oppisite side from the sensor...on the North side of the slab, and the outside temp dropped so quickly that the system didn't have time to respond with heat to prevent that loop from freezing. 

    So...I'm going to bump the heat way up, and hang a halogen light over the part of the slab that probably is frozen, and hope for the best.

    Meanwhile, what's a good source for about 20 gallons of RV anti-freeze?

  5. User avater
    johnnyd | Jan 13, 2004 05:18pm | #9

    Turned out it was frozen...two days of way above freezing temperatures (upper 30's) and last night the loop showed full flow.  Now for the glycol...what's the most economical way to buy about 20 gallons?

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