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  1. #1
    Join Date
    Oct 2004
    Posts
    18

    Concrete condensing unit pad too small

    I'm having our AC replaced and our current condensing unit concrete pad (32" x 32") is too small to support the new unit. I'm guessing this isn't an uncommon problem with the higher efficiency units having larger exchangers. I searched this thread but couldn't find anything with the same question. Sorry if it's a repeat, which it probably is.

    The installer wants to use a 3" thick resin pad (42" x 42") for the new unit beside the existing pad directly on the ground.

    Is the resin pad on the ground a better setup than trying to "extend" the pad by adding concrete blocks (CMUs)? The new pad would hang over and be supported by concrete blocks for about 10". I guess I would be concerned with the concrete pad not moving at all but the concrete blocks moving during the winter.

    I guess extending the pad with more concrete would be ideal, but my install is scheduled for Monday, and wanted to see if the above options would be okay?

    We live just outside of Washington DC, so the winters do get pretty cold.

    Thanks for any input!

  2. #2
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,962
    The resin pad will be just fine. All the pad is really doing is keeping the unit out of the dirt and level.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  3. #3
    Join Date
    May 2009
    Location
    In the Hudson Valley of New York
    Posts
    2,021
    Why not put dirt around the old pad to make it accommodate the bigger pad, and put the new pad on top? I am not sure I would want to have the old pad sitting there, with nothing on it.

  4. #4
    Join Date
    Oct 2004
    Posts
    18
    It sounds like it wouldn't be an issue to just add a few concrete blocks around the existing pad to "extend" it to accommodate the new pad on top. I'll just make sure it's level.

    This should give a more finished look than leaving the old pad just sitting there.

  5. #5
    Join Date
    Mar 2005
    Location
    Houston, Texas
    Posts
    11,874
    Quote Originally Posted by robbie 2 View Post
    It sounds like it wouldn't be an issue to just add a few concrete blocks around the existing pad to "extend" it to accommodate the new pad on top. I'll just make sure it's level.

    This should give a more finished look than leaving the old pad just sitting there.
    And what happens, when blocks start subsiding in the surronding ground? And they will. If it were me, I'd have to go with the new pad idea.

  6. #6
    Join Date
    Oct 2004
    Posts
    18
    Quote Originally Posted by the dangling wrangler View Post
    And what happens, when blocks start subsiding in the surronding ground? And they will. If it were me, I'd have to go with the new pad idea.
    Hmm... Any good way to keep them from sinking? Will a few inches of gravel underneath the blocks prevent it?

  7. #7
    Join Date
    Mar 2005
    Location
    Houston, Texas
    Posts
    11,874
    Quote Originally Posted by robbie 2 View Post
    Hmm... Any good way to keep them from sinking? Will a few inches of gravel underneath the blocks prevent it?
    Any reason they can't get another, new 3" concrete pad, and place it over the existing one?
    We can still get them around here. Solid concrete, not the styrofoam coated ones either. Believe it or not, the price is right there with the others.

    I guess gravel might work, for a while anyway.

  8. #8
    Join Date
    Feb 2004
    Location
    southern illinois
    Posts
    5,534
    why not pour a concrete pad the size you need over existing concrete pad...it's not that hard,and you probably are not in dire need of a.c. this time of year with your location.

  9. #9
    Join Date
    Oct 2004
    Posts
    18
    If I go with the plastic resin pad, should it be mounted directly on the dirt or put on top of a bed of gravel?

    Thanks

  10. #10
    Join Date
    Mar 2005
    Location
    Houston, Texas
    Posts
    11,874
    Quote Originally Posted by robbie 2 View Post
    If I go with the plastic resin pad, should it be mounted directly on the dirt or put on top of a bed of gravel?

    Thanks
    Can most of the new pad be placed over the old one? If they can, then fill in the overhang with gravel.

  11. #11
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,854
    Lift out the concrete and put the plastic one in its place. We do it all the time. I'm building a patio with the old concrete ones we haul away We sit the plastic ones on leveled dirt, no gravel or sand.
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  12. #12
    Join Date
    Dec 2001
    Location
    Ocean Pines, MD
    Posts
    7,008

    Options

    This was a quick change-out. But removed old concrete for new unit.
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    Last edited by Stamas; 03-02-2010 at 12:18 PM.

  13. #13
    Join Date
    Jan 2009
    Location
    Indiana
    Posts
    3,228
    excellent work..

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