TH> As for as energy savings, I think most places insulate the
  > perimeter walls, floor and ceiling. I think that's a shame, since
  > so much mass could be used to maintain a constant tempreture.
CH> It still does! Albeit slower because of the insulation.
And it only works if the average temperature is within the confort
zone. Yuma, Arizona might work, but Fairbanks, Alaska would not.
Still, in principle I'm with you. 
 
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