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Bluestone R value ??

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by holg, Sep 26, 2013.

  1. holg

    holg Member

    Joined:
    Feb 4, 2011
    Messages:
    53
    Loc:
    northern WI
    I reviewed some prior threads and spent some time on-line, and could not come up with R values for bluestone. The Forum has some estimates of 0.08 to 0.15 per 1 inch thickness, but nothing I could use as "official" in case my insurance carrier would like to know.

    The reason I am asking is that the Hearthstone Heritage, prior to the more recent models of putting it up on taller legs, requires an R of 1.2. My hearth plan is:

    MATERIAL R VALUE

    Frame and plywood frame top Nothing
    3 layers of 1/2" Durock: 0.39 each 1.17
    3 layers of ~ 1/8" Thin set 0.05 each (0.40 per inch) 0.15
    Total: 1.32

    Then I will have a layer of 1.25" bluestone on top.

    Knowing the bluestone value would be helpful if using the thinset values raises eyebrows.

    So if anyone knows, it would be appreciated.

    Thanks.

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  2. pen

    pen There are some who call me...mod. Staff Member

    Joined:
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    Messages:
    6,974
    Loc:
    N.E. Penna
    This source lists 0.079 for sandstone. That's pretty darn low (as is normal for rock) and probably about as close as your are going to get. Err on the low side and if you still have what you need, you are golden.

    http://www.chimneysweeponline.com/horvalue.htm

    When I first saw it's R-value years ago I cringed as I think of all the old wood stoves I've seen over the years set above a hardwood floor with nothing but a 1.5 to 2 inch thick piece of bluestone underneath <>

    pen
  3. Waulie

    Waulie Minister of Fire

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    Nothern Lower Michigan
    It shouldn't matter. I mean, you've got your required R-value in the Durock itself, seeing as how keeping the hundredths place is a little silly. I would just roll with it knowing the obvious fact that you have more than enough. If anyone throws a fit (which I highly doubt), you could contact various stone suppliers/quarries and get an answer. I wouldn't go through the hassle unless someone asks
  4. holg

    holg Member

    Joined:
    Feb 4, 2011
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    Loc:
    northern WI
    Wualie and pen--thanks for the advice. Think I'll go with what I have and call it good.
  5. stoveguy13

    stoveguy13 Minister of Fire

    Joined:
    Dec 15, 2006
    Messages:
    985
    Loc:
    CT
    where did you get get the r value for the Durock? Hearthstone lis it at only .20
  6. begreen

    begreen Mooderator Staff Member

    Joined:
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    Messages:
    46,729
    Loc:
    South Puget Sound, WA
    Hearthstone got it wrong. That sounds more like Hardibacker's R value. The original Durock cement board had an R value of .52 per inch or .26/ .5". Durock NexGen is all you can get now. It has an R value of .78 per inch or .39/ .5" sheet. Tom at the Chimneysweep has a pretty good, up to date chart. Pen listed the link above.

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