Mike Winfrey : 1st -you will need a Total final vapor barrier for the top of your compost. Nothing spoils ether the heating potential or the insulating potential than
water .
Also Ether wet
hay or Manure will stain your concrete, not necessarily a problem with your slab but unsightly around the base of your house .
A minimum mass needed to start producing heat without losing too much heat
energy to the cooling potential of the concrete mass Would be close to 4' X 4' or
possibly bigger And this mound heaped up against the side of the house is potentially as long as the entire perimeter of your structure !
as this mound of material will both settle and slump eventually your mound will take on a cross-sectional shape similar to a 1/4 pie slice or section .
If you have the amount of mass to make this work go for it , if you can only cover part of your perimeter i would recommend doing it on the Windy side of the house
doing everything you can to keep your compost pile as dry as possible !
I hope this is timely and helpful, for the Good of the Craft ! Big AL