Hi I am building a home in Northern New Hampshire and I would like to install a geothermal system.  I have run radiant in my slab already but I am stumped on what would be the best distribution system throughout the rest of the house.  Folks tell me to continue with radiant throughout the entire house but the cost is enormous for installation.  Any thoughts on a hybrid system using radiant in the slap and hot air throughout the house?  Or baseboard/radiators and the radiant?  Is geothermal more effecient using air or water?

Thanks

Do you want AC?

No, I do not need AC. 

Combo systems using hot water for radiant and hot forced air are common. Baseboard radiant is not an option with geo. You can do your forced air by having air handlers in different parts of the house. This will minimize duct work, or you can get a combo heat pump that does both hot water and hot air. Are you working with a geo installer or going it on your own?

Water to water geo tends to have lower C.O.P.'s. Who designed the radiant in the slab now? If it isn't designed for relatively low geo temps, you may not have the density required.
I don't know where your house is, but in this day and age, not (at least) prepping for a/c may have a very negative impact on home value/sale-ability.
J