?why put foam insulation under a radiant slab?

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Offline CZARCAR

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?why put foam insulation under a radiant slab?
« on: 16/05/2011 20:24:42 »
6" concrete slab with water pipes running thru it to heat the slab.If the perimeter of the slab is well insulated so to minimize perimeter heatloss & the heat can only conduct down into the gravel below, will it eventually rise back up from the ground & assist the slab for its heating?

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Offline Geezer

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?why put foam insulation under a radiant slab?
« Reply #1 on: 16/05/2011 21:30:49 »
Some of the energy that goes into heating the gravel will be returned to the building, but some of it will escape underground beyond the perimeter of the building and be wasted. The thermal mass of the concrete slab is probably quite sufficient to moderate the temperature, so it makes sense to include insulation underneath it.
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