Building s stone hearth pad for Harman

99miles Posted By 99miles, Aug 18, 2009 at 4:51 AM

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  1. 99miles

    99miles
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    Sep 19, 2009
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    Portland, OR
    I have a Harman XXV coming on Wednesday! Now I need to build the hearth pad.

    I picked out the stone I want -- I think it's called Emerald Bluestone (or something like that).

    My plan is to make a frame of 2x4's (on their sides). Then plywood on top, then hardiebacker. Then I'll cement the stones in. So, 2x4 + plywood + hardiebacker will make it about 5 or so inches tall, before the stones are applied. Ideally i would like to stone the sides as well, but the stones are bigger so I'd have to break them and apply them. Is this going to be a nightmare? Any tips on this, or on how to make the edges clean? The other option is to have wood sides, but that's not as appealing to me.
     
  2. CarbonNeutral

    CarbonNeutral
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    Jan 20, 2009
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    What's the required r-value on that stove, because at the moment, you don't have much - plywood, hardibacker, and studs are all combustible. Stone is a poor insulator/good conductor (relatively)

    If you need a hearth with anything more than ember protection, I would go with metal studs and concrete board (the heavy stuff, not the light stuff)
     
  3. 99miles

    99miles
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    Sep 19, 2009
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    I don't see anywhere that lists the R-Value for the Harman XXV. Not sure where to find that info.
    But I just did a project with Hardibacker -- it is a cement board, claims to be non-combustible, and it's definitely not light.
    That plus the stones isn't enough? I've been reading of other people building them this way, and the people I bought the stove from said this would be fine, but if it's not I'd rather find out now before I've built it.
    Thanks.
     
  4. Wood Heat Stoves

    Wood Heat Stoves
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    Jun 12, 2009
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    hearthpad science for ya, your design is probably fine though, check your manual, many require no specific r value
    Floor protector’s come with various types of
    specifications. To convert a floor protector’s specification
    to an R-value, do one of the following:
    • If the R-value is given, use that value—no
    conversion is needed.
    • If a K-factor is given with a required thickness
    (T) in inches, use this formula: R-value = 1/K x
    T
    • If a C-factor is given, use the formula: R-value =
    1/C
    To determine the R-value of the proposed alternate floor
    protector:
    • Use either the K-factor or the C-factor formula
    explained above to convert specifications not
    expressed as R-values.
    • For multiple layers of floor protectors, simply
    add the R-values of each layer to determine the
    overall R-value of the layers.
    If the overall R-value of your setup is greater than the
    R-value of the specified floor protector, then your setup is
    acceptable.
    Noncombustible Material Thickness R-value
    Gypsum or plaster board1 1/2″ 0.45
    Wallboard, Wonderboard, or Durock 1/2″ 0.20
    Ceramic board (Fiberfrax or Micor)1 1/2″ 1.10
    Nominal solid clay brick 1″ 0.20
    Ceramic wall or floor tile 1/4″ 0.01
    Mineral wool insulation 1″ 3.12
    Cement mortar 1″ 0.20
    Horizontal still air2 * 1/8″ 0.92
     
  5. CarbonNeutral

    CarbonNeutral
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    Jan 20, 2009
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    Wonderboard and Durock are the brand names for cement plus fiber glass mesh - they are also listed in the r-values above. Hardibacker is much lighter in color, and a bit lighter in weight. From this forum I have seen stated that it has an organic filler that means that it cannot be considered non-combustible for this purpose.
     
  6. begreen

    begreen
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    I'm going to assume that considering this is a pellet stove on a pedestal, that all that is required is a non-combustible surface. If yes, Hardibacker should be ok. Moving to pellet forum for more direct input.
     
  7. HEMI

    HEMI
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    Aug 17, 2009
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    Loc:
    connecticut
    i built a hearth the same way, 2x4 on their sides to raise it, plywood, cement board then the slate stone tiles, then went up the wall 6ft with the cement board and tiles.
     
  8. bobforsaken

    bobforsaken
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    Oct 2, 2009
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    I'm about to undergo the same process for the same stove. I'm pretty sure looking at the clearances that it only requires 1 inch clearance on the bottom for combustibles. What I don't know is.. is that 1" from the bottom of the legs or from the bottom of the stove. My construction plan is going to be nearly identical in terms of Plywood, hardibacker and stone. (leftover granite tile) I wasn't sure whether or not I was going to raise it on 2x4's however. What would be the reasoning for this? Is it just for looks or to get necessary clearance if it were a wood stove instead of an XXV?
     
  9. nailed_nailer

    nailed_nailer
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    Oct 29, 2007
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    I just looked at the installation Manual for the Harmon XXV here.
    http://hearthnhome.com/downloads/installManuals/xxvm.pdf

    If I read it correctly all you need under the stove is a non-combustible material under the stove and any horizontal venting.
    It requires minimum 6" in front of stove, 2" to the sides and 0" to rear of hopper.
    The non-combustible material can be as little as a sheet of 20 gauge sheet metal.

    I built mine out of paving stones.

    I laid out a corner of my living room and created a shape that would conform to the specifications in my Enviro manual.
    I laid down a sheet of 3/4" ply in the shape I wanted.
    I covered that with Durock. I then used thinset adhesive to bond Grey pavestones in the pattern I liked.
    Once that cured I filled the stone gaps with polymeric sand and water misted them into place. Whole thing cost me less than $100 and looks great.
    I wrapped the face side of the "hearth" with a nice piece of oak trim.

    Here is how it came out.

    [​IMG]

    (Photobucket seems to be having problems. It is the stove install in my Avatar)

    It has been in service now for about 2 years and shows no signs of wear.

    Good Luck,
    ---Nailer---
     
  10. Dr_Drum

    Dr_Drum
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    Jan 7, 2009
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    This is what I was told as well from the dealer. You only need contact protection against a combustible surface. That is, hot pellets laying directly on the sheet metal wont conduct enough heat to ignite the floor. That is why those sheet metal pans the sell in the box stores as a generic hearth pad are acceptable. I went with something a bit more substantial, but mostly for appearance.
    Mike -
     
  11. HEMI

    HEMI
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    Aug 17, 2009
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    connecticut
    heres how i did mine
     

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  12. mnkywrnch

    mnkywrnch
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    Dec 8, 2008
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    Very nice Hemi!
     
  13. amick780

    amick780
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    Jun 27, 2009
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    I did mine the same way only I did not build the stove up...makes it more difficult to clean having to kneel on a small step like that, but hardy backer is fine to use. If you do build it up make sure you use enough bracing (2x4's) the stove is extremely heavy an will crack your stone if the plywood/hardybacker gives under the stove.
     

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  14. tinkabranc

    tinkabranc
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    Oct 23, 2007
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    Mine is just sitting on a hearthpad that is made out of 1/2" Plywood, a layer of
    hardibacker and then porcelain tile. My Advance is just sitting on a piece
    of granite remnant.

    Pad must non combustible and meet or exceed the minimum width requirements
    in the manual.
     

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  15. jtakeman

    jtakeman
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    Dec 30, 2008
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    hemi, amick and tink!

    Nice work and all nice looking too!

    jay
     
  16. imacman

    imacman
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    Beautiful hearth, Amick!
     
  17. lessoil

    lessoil
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    May 31, 2008
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    Link to the pad I made.
    http://www.hearth.com/econtent/index.php/forums/viewthread/22059
    Used 2x4's on edge for frame; plywood then fire board (Cement Board) then the tiles.
    Trim is plain 'ol pine.
    Had to make it this tall so the pipes would clear the top of the baseboard.
     
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