I have just contracted a company for drilling a 650 feet deep well for a 9kW heat pump. The drilling cost is about €5500 or $7200. The heat pump costs about €7500 ($9600). Add installation and the total is about €15000. I already have radiant floor heating and radiators since I've been burning oil until now.
They don't usually drill multiple wells here unless you need more than ~700 feet depth which means 11kW pump and up.
Year average COP should be about 3.5, time to earn back is about 10 years with todays oil price, much less if it hits $100 :)
I've never heard someone reporting a year average COP of more than 4. Still, when already at 3.5 or so, higher COPs mater less and less. The difference in savings from 2 to 3 is huge, from 4 to 5 is miniscule in comparisation.
