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Heated slab

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  • Pennbo's
    The biggest heat loss from slabs comes from the part showing ABOVE the ground. So if you insulate nothing else you might want to insulate that. When we were
    Message 1 of 2 , Aug 1, 2008
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      The biggest heat loss from slabs comes from the part showing ABOVE the
      ground. So if you insulate nothing else you might want to insulate that.
      When we were building we had our heating engineer run the calcs that
      showed the relative heat loss of the slab in various spots. The contact
      with air is what pulls the heat so quickly from the slab above ground.
      The contact with the ground is actually not as bad and the loss
      decreases with time each heating season. I don't remember the exact
      numbers but it was a big difference with the under-slab losses being
      somewhat minimal. We still insulated under slab. What we didn't insulate
      was the perimeter below grade. Extremely problematic in our case. We
      decided we would save more energy by actually getting the darn house
      built and lived in then by spending more time and nerves trying to solve
      that particular issue. We don't feel we are losing much heat to the
      ground from that area anyway. The area below grade is also below the
      bottom of the slab- which IS insulated.

      We have radiant heat using hydronics. We have often talked about the
      idea of using the earth to preheat everything. If you live in an area
      where you can easily dig deep enough to take advantage of the stable
      core temp it's a good bet. We live where about 10 feet down it's solid
      rock....

      Chris
      > Hi Donna;
      > >
      > > Remember that in your climate the stabile ground temperature
      > > is about 41°F/5°C, and rock has almost no insulation value.
      > > So you will need to insulate the entire area of slab, very well,
      > > or it will constantly suck the heat out of your well insulated
      > > house. That is in addition to the perimeter insulation, to stop
      > > the slab from sucking heat under the thick walls, to outdoors.
      > >
    • David Neeley
      As I recall, you are in California. Ground temperatures there are roughly in the comfort zone, so loss of heat would not be an issue for you. If I also recall
      Message 2 of 2 , Aug 1, 2008
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        As I recall, you are in California. Ground temperatures there are
        roughly in the comfort zone, so loss of heat would not be an issue for
        you.

        If I also recall correctly, the discussion revolved around a home in
        Maine. Ground temperatures there are *much* colder, and would be a
        permanent heat sink to rob you of heat from the slab.

        For them, sub-slab insulation is a requirement for long term success
        and comfort. For you, it might actually be counterproductive.

        It all depends upon location...

        David

        On Fri, Aug 1, 2008 at 10:21 AM, Pennbo's <pennbo@...> wrote:
        > The biggest heat loss from slabs comes from the part showing ABOVE the
        > ground. So if you insulate nothing else you might want to insulate that.
        > When we were building we had our heating engineer run the calcs that
        > showed the relative heat loss of the slab in various spots.
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