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Thread: foam block under water heater?

  1. #16
    DIY Member charles2's Avatar
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    Quote Originally Posted by Dana View Post
    The feet have to extend to something structural, not resting on foam.
    Since concrete building foundations are sometimes poured over foam, perhaps foam of sufficient density can be regarded as structural?

  2. #17
    Forum Admin, Expert Plumber Terry's Avatar
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    A gas water heater has a fire chamber below.
    Setting it on foam would be useless.

    It only makes sense with electric.

  3. #18
    DIY Member charles2's Avatar
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    Terry, does it also make sense with sealed combustion gas?

  4. #19
    Moderator & Master Plumber hj's Avatar
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    Default foam

    NO! There is NO contact between the storage tank and the bottom of the heater.

  5. #20
    DIY Member charles2's Avatar
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    HJ, I don't understand what you're saying. Would you explain a little more? Could the foam catch on fire being so close to the fire chamber on a sealed combustion heater?

  6. #21
    Apprentice Plumber D'Brie's Avatar
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    Quote Originally Posted by Terry View Post
    In the Seattle area, we install electric water heaters on foam pads.
    We buy them from the supplier that supplies the water heaters.
    Same here in Whatcom Co. Washington.

  7. #22
    Moderator & Master Plumber hj's Avatar
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    Default foam

    "Foundations" are NOT poured over foam. Floor slabs are, or foam can be inserted around the floor perimeter. The foam under a slab is subjected to such ridiculously low loadings that the concrete will NEVER compress it.

  8. #23
    In the trades Dana's Avatar
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    Quote Originally Posted by charles2 View Post
    Since concrete building foundations are sometimes poured over foam, perhaps foam of sufficient density can be regarded as structural?
    Not exactly a good argument. The concrete slab can handle 500psi, but disburses that weight over a much wider area of the foam. Putting any type of rigid skin over the foam gives it a structural monocoque with much higher mechanical ratings. (the OSB EPS OSB sandwich is a standard structural-insulated-panel aka "SIP", and stronger than either matieral on their own.)

    But like I posted, standard 2lb density XPS can handle 25psi with 10% compression, which is 3600lbs per square foot,and you only need ~275psf. The footprint of a 20" diameter tanks is ~2.2 square feet, so nominally it'll carry the ~600lb load of a flat bottomed 50 gallon tank pretty handily in a static load condition. (600lbs over 2.2 square feet it a bit under 2psi, less than 8% of the load rating for XPS that yields 10% compression. I think you'd be good. 1.5lb EPS would probably be fine as well.

  9. #24
    DIY Member charles2's Avatar
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    Quote Originally Posted by hj View Post
    "Foundations" are NOT poured over foam.
    See Figures 7, 9 and 14 of this document:

    http://www.toolbase.org/PDF/DesignGu...dFPSFguide.pdf

  10. #25
    In the trades Dana's Avatar
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    Quote Originally Posted by charles2 View Post
    See Figures 7, 9 and 14 of this document:

    http://www.toolbase.org/PDF/DesignGu...dFPSFguide.pdf
    FWIW, foundations poured over foam in the figures cited are unheated spaces only.

    Table 2 gives you the allowable load per square foot, not just per square inch, which reliably answers the question.

  11. #26
    DIY Junior Member Tail's Avatar
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    Terry, does the foam pad you get from your supplier have a product name? I am getting ready to swap out my electric tank and would like to get a pad to set the new tank on but I am having a hard time finding anything of this nature in Ohio.

  12. #27
    DIY Junior Member bobwilli's Avatar
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    Default foam block under water heater?

    Quote Originally Posted by Terry View Post
    In the Seattle area, we install electric water heaters on foam pads.
    We buy them from the supplier that supplies the water heaters.
    Do you install the heater directly on the pad, which in turn is in a drain pan?

    I have a GE GeoSpring 50 gal heat pump hybrid water heater to install.

    Thanks.

  13. #28
    George the Plumber Gsalet's Avatar
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    OK Guys put a piece of plywood on top of the foam, problem solved<GRIN>

  14. #29
    DIY Junior Member bobwilli's Avatar
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    Default foam block under water heater?

    Thank you guys for your advice. You're a valuable resource. Here's what I did: put the water heater directly on the foam pad, which is in a drain pan on a plywood stand. The water heater went easily on the foam pad and didn't seem to compress it much. Of course it was empty. Filled it doesn't seem to either. Anybody see a problem with this?

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  15. #30
    Forum Admin, Expert Plumber Terry's Avatar
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    It should be fine.
    We just place the electric heaters on the foam pads.

    I'm surprised that "plumbingpro" would add plywood over the foam. I've never seen that done in all my years plumbing.

    You will need to Earthquake Strap though, you're on the West Coast.

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