Buckley Rumford Fireplaces
Soapstone or Firebrick?
A Discussion about Heat Capacity
9/13/11

On Sep 13, 2011, Mark wrote:

I am considering replacing my firebrick in two wood burners (free standing) with your soapstone firebrick product. I have a couple questions though:

First: by replacing normal firebrick with soapstone will I damage the stoves in any way with the hotter fire?

    No reason to believe the fire will be hotter. The soapstone is just heavier and has slightly more thermal mass so will take and little longer to heat up and will hold the heat a little longer.
Second: by replacing with soapstone will I need to increase the required clearance space from combustibles?
    No. Again, no reason to believe the fire (or the stove) will be hotter - just a little slower to heat up and a little slower to cool off.
Third: will I see enough increase in prolonged heat time to make it worth the change out?
    We would love to sell you the soapstone but soapstone has virtually no more heat capacity than firebrick. The specific heat of water is 1 calorie/gram °C which is higher than any other common substance. The specific heat of firebrick and soapstone are both about 0.24 calorie/gram °C. The difference between soapstone and firebrick is the density, or weight. Firebrick weighs 2,403 kg/m³ while soapstone weighs 2,980 kg/m³ So, for a given thickness (say 2") the soapstone would weigh about 20% more than the firebrick and have about 20% more heat capacity expressed in terms of calories per gram. You could get the same heat capacity from firebrick by making it 20% thicker or about 2-3/8" instead of 2" thick.
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Referrences
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/spht.html
http://www.tulikivi.com/usa-can/fireplaces/Soapstone_Characteristics_Fireplaces
http://www.engineeringtoolbox.com/specific-heat-solids-d_154.html
http://physics.info/heat-sensible

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