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Radiant heat and Sand

This may be an odd one, but last week I ran into a job where the homeowner did his own radiant work and used sand instead of gypcrete. He layed his tubing down on his subfloor, poured sand over and around it and then placed hard wood floor over it. His builder said he did it all the time because it was cheaper. The boiler guru at our supply house said that heating it over 120F would crystalize the sand and turn it into an insulator. Anyone else have any info on whether or not that might be true?

Thanks!

Comments

  • kpc_41
    kpc_41 Member Posts: 7
    for some ....

    strange reason there is that snakeoil about sand and radiant....supply house is right about the cystalization. get the sign off on the tubing install.
  • jp_2
    jp_2 Member Posts: 1,935
    off a little in temp

    I think you're off a little in temp, melting point of sand is more around 2500F?

    sand in itself is considered more of an insulator than a conductor to begin with.
  • Rich L.
    Rich L. Member Posts: 414
    Sand...

    One of the biggest problems with sand is the insulating value. Actually it's all the little air spaces between the sand particles. Picture a HOT sunny day at the beach, one of those you can barely walk across the sand to the water. If you can stand still long enough on that hot sand, wiggle your feet a bit. As soon as you get an inch or two below the surface you feel that nice cool sand right? Sand just is not a good conductor or heat sink (thermal mass) for radiant.

    I've never heard of the sand in floors crystalizing over 120 degrees. I would think you'd have to be in the 1000's of degrees before worrying about that.

    Lots of good reasons out there NOT to use sand. It's been discussed in this forum before. Do a search for sand and radiant.

    Good luck, Rich L
  • Sand,,,

    crystalizing at 120*? That's a good one! ;)
  • it may not be such

    a bad idea

    crystallization; absolutely not. and at a 'depth' of 3/4", it would be a decent, less expensive, easier/quicker way to create thermal mass. def better than doing nothing/air pockets
  • troy_8
    troy_8 Member Posts: 109
    Sand-Not just an insulator

    Sand also will make this the dustiest home you have ever owned. It will sift through cracks for ever. You need to solidify that sand and fill the voids between the grains. Batt insulation is nothing more than a sponge of air. Sand isn't that different. Fill batt insulation with water and it doesn't insulate. Sand is the same. Wet it and it conducts heat. Dry it and it won't conduct.
  • hot_rod
    hot_rod Member Posts: 21,804
    when it's wet

    sand is a good conductor. Consider some pin holes in the tube to keep the sand moist to transfer energy :) Just kidding.

    Sand likes to slip away also, reminding us of the hourglass. Any cracks or shrinkage in the flooring would allow sand to slip away.

    Adding some portland, for a few bucks a bag, and inexpensive water (aka cement) would provide much better heat transfer and storage.

    But if the flooring is not in contact with the sand of "mix" you lose the most important means of energy transfer anyway, conduction.

    Sounds like a good project for "Myth Busters"

    hr
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
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