Yes, geothermal systems can be installed in existing homes. The installation process typically involves drilling a series of wells in the yard, connecting the wells to a heat pump, and running the necessary piping and wiring to the interior of the home. The installation process can be complex and may require the services of a qualified HVAC technician. Additionally, the cost of installation can be high, but the long-term savings in energy costs can make geothermal systems a worthwhile investment.