They won't make it cheaper than if you had less house. Actually, more mass (book mass, or any other kind) does make HVAC cheaper: http://static.monolithic.com/

They won't make it cheaper than if you had less house. Actually, more mass (book mass, or any other kind) does make HVAC cheaper: http://static.monolithic.com/pres/rvalue http://static.monolithic.com/pres/rvalue The California Handbook for Solar Energy is the only government publication we have been able to find which takes into account the thermal mass of the concrete when measuring heat loss. Simply stated, the concrete acts as a heat sink which slows the passage of heat back and forth through the wall or roof assembly.