Do not have AC, just in floor hot water supplied by a geo Thermal system.  Water temp is approx 110F.   I am looking for some ideas on the pros and cons of various thermostats and settings.   Right now the stat is a cheap Big Box store 24V stat.   It appears to not keep the floor and room comfortable even though set for 70F.   Floor cools down and takes a while to get up to a toasty level.     It is a wall mount and measures air temperature.

Azel makes thermostats that also have a floor sensor (not sure how you get it into the slab though). http://www.azeltec.com/catalog.0.html.0.html It can work on a combination of air and floor temp to regulate the room temp. I would suggest starting there and searching for similar products by other manufacturers.

Unnecessary in the vast majority of applications, new, retro, residential and commercial.

BB MN, Are you saying an infloor sensor is unnecessary? How about an outdoor sensor? Dave

Outdoor sensors are a must; increasing system efficiency and comfort. If you have a condensing boiler an outdoor reset (properly programmed) will increase combustion efficiency as well.

Unfortunately, I find many outdoor sensors still in the box on the "inside" of the ModCon boiler cabinet! They definitley don't work like that.

Look for some type of PID thermostat to account for the slow reaction time and overshoots.

Slow reaction time and "overshoots" are more a factor of insulation and overall control system design. PID is more common in commercial applications.

I have to disagree with morgan. I find floor sensing to be a very nice and economical addition to radiant system control. it's ridiculous to have paid for warm floors that may end up cold between heat demands.

A tekmar 508 offers that as well as the ability to set the thermostat for different kinds of emitters (convective, high mass, etc). very powerful stuff.