I have decided to go ahead with a Geo system which uses both infloor heat as well as hot air. I understand that the radiant portion of the system is only for comfort and the temp of the water is kept at 80-85 degrees F. My question is if I need a outside probe for the the radiant portion of the heating system(I do not have the proper name-this probe measures the outside temp and adjusts or anticipates the water temp inside). The hot air portion will have a outside probe(this will be a Honeywell Vision Pro). Some contractors use a probe with radiant while another feels that since the radiant flooring is just comfort(I understand that a small portion of the house overall heat will be coming from the floor)it is not neccessary. What do you think? Any help or opinions would be appreciated.

Because your useing the radiant system as a floor warming system , as opposed to a space heating system . I say modulating the water temp based on outdoor temp might be overkill .  If you want to use radiant as your primary heat its a must

I would agree, our radiant flooring will keep the house warm to about 15F, below that and the furnace starts to cycle. We are circulating 90F water through the radiant tubes.

Maybe if you’re thinking of overheating the space in 30F or 40F weather you might want a thermostat. I just let ours run 70% of the time (off peak electricity) when we are 30F or above or some times I play with zones, below about 25F I let it run 100%.

Outdoor reset is the term used for what you are describing and I would recommend installing it.

Thank you for the feedback. We are now considering using either the Honeywell Vision series or the Techmar line of controls for the radiant controls. Does anyone have a preference or recommendations?

the honeywell system would have to be the aquatrol aq2000 , which I have not used but honeywell is allways a safe gamble
I have used the Techmar controll countless times and and its a great product

after a little research on the honeywell product the Tekmar is much better

If the intent is to maintain the infloor water at 80-85 all the time as stated in initial post, what would be the role of outdoor temperature reset control?

I second Engineer's question. I don't see the purpose of any outdoor reset control in that situation, other than for the installer to sell more stuff and raise the price.