K to R conversion for hearth pad

[sergio]

The stove specifies the floor protection to be “2 layers of 3/8 inch millboard having a thermal conductivity K of less than or equal to 0.84 btu in/ft/sq. h. degrees F or the equivalent protection shall extend at least 16 inches in front and at least 8 inches to each side of the fuel loading door and beyond the back of the stove.” I found 2 different K to R conversions on this web site. One is R=(1/(Kx12))xThickness which would yield a total R=(1/(.84x12))x3/8=.074 The other is R=(1/K)xThickness which would yield R=(1/.84)(3/8)2=.893 . So which formula is correct? Does a 36"x36"x2" thick reinforced concrete block have enough R value to meet the requirements?

Thanks for your help


Sergio

 

[Corey]

I have only seen it as K=1/R which would seem to make sense because one is conductance, the other is resistance, so they should be inverse. Looks like those equations are trying to account for total K or total R by taking into account inches.

Most R figures I have seen for poured concrete are .08-.09 per inch, so 2" thick would be R .16 - .18 (or K = 1/.16 to 1/.18, so K= 5.55 - 6.25), which does not meet the specification.