Here is some more information.
"Drilling Costs
Drilling costs for a geothermal pump system can run from $10,000 to $30,000, depending on the size of the system and the type of ground that has to be drilled. These drilling costs have to be added to the cost of the heat pump system when calculating the total cost of a geothermal heat pump installation.
System Cost
Geothermal heat pump systems cost around $2500 to $3000 per ton of capacity. Given that an average to somewhat larger home will require three tons of heating/cooling capacity, the cost comes to about $7500 to $9000 for the actual geothermal heat pump equipment.
Cost Comparison
Assuming average costs, the total cost of a three-ton geothermal heat pump system would be $8250 for the heat pump and $15,000 for the drilling, for a total of $23,250. A traditional electrical heating and cooling system costs around $4000 a ton, so an equivalent three-ton traditional heating/cooling system would cost around $12,000. However, keep in mind that the utility bills of homeowners with geothermal heat pump systems tend to average 20 to 30 percent less than homeowners with traditional heat/cooling systems. Assuming a savings of $80 a month on your utilities, the extra $12,000 you paid up front for the geothermal pump system will be recouped in 13 years (and geothermal pump systems last 20 to 25 years, on average)."
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