i actually work for a company and we install and service geothermal heat pumps. basically if your building a new house, youd be stupid not to put one in just because its way easier and nothings in the way. and you dont have to worry about the yard getting torn up by the drillers or excavators. no one we installed systems for has ever complained about their electric bill since switching over. one house i know for sure is about 4000 square feet and their electric bill is 200 a month, they have 2 geothermal systems in their house. also depending on which systems you go with you can choose the option of running radiant floor heat off the system as well. most systems offer desuperheater options on them which is basically recirculating and making hot water for your house, so you will also save there, and trust me, these things do produce probably 20-30 percent of the hot water! oh and the warrantys, if you go with some of the better companies such as water furnace or climatemaster, you will get a 10 year parts and labor warranty on the units. which is way better than a typical hvac system which is usually only 5 year parts and 1 year labor. yes the best way would be to do a closed system say in a pond but you will need a fairly decent sized pond if your house is larger. but typically if your doing a vertical closed loop system its 150-200 feet per ton. ussually well drilling costs will be somewhere in the 15-20 bucks a foot depending on the driller. but until 2016 the government is offering a 30% tax rebate on installation of geothermal systems, that includes the well drilling as well.