LJKeenan
You are right on 1 article here. The in-slab heating is the best and it is done with a tube spacing of 12"
Now there are a couple options for heating a floor hydronically for a wood frame home one is the self-leveling gypcrete pour on a wood floor however its heavy and its thickness has some further complications with an additional 1-1/2"-2-1/2 with doors etc.
This system I'm using is the Uponor/Wirsbo system and it only raises the floor an additional 1/2" The tubing is about 7/16 OD x 5/16 Id and is cross-linked to prevent oxygen from entering the water and causing corrosion issues long term. The tube to tube spacing is a tried and true 7" that will spread heat uniformly through most floor coverings. And of coarse stone would be one of the better granite for our installation.
The under floor method of which you are writing otherwise known as staple up is wrong on so many levels. I had originally had this installed beneath two second story rooms and even with water temps of 180 Deg F. the rooms were uncomfortably cold. It was all removed for this system mentioned above. ( I WOULD STRONGLY ADVISE AGAINST ANY TYPE OF STAPLE-UP!!!)
I may add that our home boosts the in-slab heating for the main floor and is heated via solar and backed up with geo-thermal. The in-slab is sooo nice during the winter months and very efficient and we live in a harsher type climate.
Randen
