Agree.. I ran blue board stright down below the frostline on a pre-existing slab and works like a champ. Also in for insulation I used 2lb closed cell foam to make a water tight seal and I seem to loose no heat at all in the floors or the walls when it -5 degrees.
On new home construction it...
Take a look at "The Nest" Thermostat. I have one that is in sync with my smartphone and is able to be adjusted via wifi. This thermostat monitors patterns of use as well so it is also able to self adjust after it is done learning usage patterns. It is a fantastic product not to mention it looks...