foam block under water heater?

Discussion in 'Water Heater Forum, Tanks' started by charles2, Dec 21, 2009.

  1. D'Brie

    D'Brie Apprentice Plumber

    Messages:
    44
    Location:
    NW Washington State
    Same here in Whatcom Co. Washington.
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,615
    Location:
    Cave Creek, Arizona
    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.
  3. Dana

    Dana In the trades

    Messages:
    2,837
    Location:
    01609
    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.
  4. charles2

    charles2 New Member

    Messages:
    54
    Location:
    Georgia
  5. Dana

    Dana In the trades

    Messages:
    2,837
    Location:
    01609
    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.
  6. Tail

    Tail New Member

    Messages:
    6
    Location:
    Ohio
    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.
  7. bobwilli

    bobwilli New Member

    Messages:
    10
    Location:
    Salem, Oregon
    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.
  8. Gsalet

    Gsalet George the Plumber

    Messages:
    83
    Location:
    San Francisco
    OK Guys put a piece of plywood on top of the foam, problem solved<GRIN>
  9. bobwilli

    bobwilli New Member

    Messages:
    10
    Location:
    Salem, Oregon
    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?

    Hybrid Water Heater installed clipped - 8-28-10 - IMG_2056.jpg
  10. Terry

    Terry Administrator Staff Member

    Messages:
    15,000
    Location:
    Bothell, Washington
    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.
  11. Gsalet

    Gsalet George the Plumber

    Messages:
    83
    Location:
    San Francisco
    I would just use foam myself but the plywood would keep legs from digging in from the top if it had legs. seamed to be a lot of energy about that <Grin>
  12. seattleplumber

    seattleplumber Service plumber.

    Messages:
    20
    Location:
    Seattle, WA
    If it has feet, you don't need a pad...

    The whole point of the pad is to eliminate heat loss due to direct contact with the concrete floor. If the tank has feet that are more than just dimples in the sheet metal, a pad isn't necessary. Therefore, you wouldn't need to place a water heater with feet on a pad to begin with. That being said, if you try it the weight will sink the feet right through the pad. And if it's gas, it will melt the foam (seen it on an old style gas water heater).
  13. InterociterOperator

    InterociterOperator New Member

    Messages:
    2
    Location:
    Oregon
    Washington State Iinstallation Code

    I was advised that the Washington State Installation code now requires the foam pad on electric water heater installs.
    Even with the new heaters there is significant heat loss from the bottom of the heater to the cold dense concrete floor below.
    Insulfoam makes the high-density "Insulpad Electric Water Heater Insulation" pad (7-32813-10043-0) $11.87 at Home Depot.
    I'd prefer to put in under the drip pan and get a little height for drainage, but I've never seen it installed that way.


    (It makes a poor frisbie)
  14. charles2

    charles2 New Member

    Messages:
    54
    Location:
    Georgia
    Got a link? I searched for this at homedepot.com and came up empty.
  15. InterociterOperator

    InterociterOperator New Member

    Messages:
    2
    Location:
    Oregon
  16. charles2

    charles2 New Member

    Messages:
    54
    Location:
    Georgia
    I guess it didn't come up because it's only available in stores. 2" seems a little thin - I'd like to see about 12", but of course you could stack them.
  17. Terry

    Terry Administrator Staff Member

    Messages:
    15,000
    Location:
    Bothell, Washington
    2" is plenty. It's closed cell foam. I don't know if you ever sat on a small wafer of closed cell foam on snow before, but it colds the cold very well. When I sleep on snow, having just a thin pad to sleep on works wonders.

    I have seen drain pans installed over the 2" foam before. It's a good way to install them.

    [​IMG]
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