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Hearth Extension Substarte

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by pine138, Dec 10, 2011.

  1. pine138

    pine138 New Member

    Joined:
    Dec 6, 2011
    Messages:
    1
    Loc:
    Southwestern Maine
    I am in the process of replacing my old wood insert with a new one and let me tell you, it has been quite the learning experience! Anyway, one of the things I have learned is that I need to install a hearth extension for my fireplace. My fireplace has a 17" brick hearth that is raised 10 inches above the plywood subfloor. The user manual of the stove I intend to buy indicates a minimum thickness of 0.5 inches and a thermal conductivity K factor of 0.84. If I did my research and math correctly, that translates to a R factor of 0.05 using the formula R = (1/K x 12) x T, where T = thickness in inches. Given that Durock cement board has an R of 0.26 per half inch, I am thinking that I will be OK with a 0.5 inch Durock substrate. Is that correct? Also, is there a special kind of thinset that should be used?

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  2. raybonz

    raybonz Minister of Fire

    Joined:
    Feb 5, 2008
    Messages:
    6,205
    Loc:
    Carver, MA.
    Welcome to the forum pine! Durock Nexgen has an R-value of 0.39 per 1/2" the original Durock was 0.26.. I used thinset cement between the floor and the cement board and between all other layers.. Have fun!

    Ray

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