Choose the type of heat pump based on your climate. Choose an air source heat pump for areas where the outside temperature rarely goes below 40 degrees Fahrenheit. Choose to keep your existing furnace as backup heat if you live in a colder climate or choose a more expensive geothermal heat pump to replace your furnace. Choose a water source heat pump if you have a well which can supply the water; otherwise, choose a ground source heat pump. Select a heat pump which will give the same heat output as your existing furnace.
Install the outside part of the heat pump you have selected. Hire a licensed professional to install the air source heat pump unit outside, close to where the inside part will be located. Ask him to run the refrigerant pipes inside to the location of the inside heat exchanger. Hire a contractor experienced in geothermal heat pumps to install the outside piping, buried in the ground for ground source heat pumps or bringing water from a well for water source heat pumps. Have the piping brought inside to the location where the heat pump will be installed.
Install the heat pump you have selected. Install the air source heat pump heat exchanger in the existing forced air ducts before or after the existing furnace, if it will be retained for back-up heat. Connect the heat exchanger to the refrigerant lines.
Remove the existing furnace if it is not needed for back-up heat. Install the heat pump. Connect the water pipes coming in from outside, as per the manufacturer's instructions. Connect the electrical supply as specified by the manufacturer.
Change the forced air ductwork to accommodate the new heat pump. Change the main ducts to match the air manifolds at the input and output of the new heat pump. Add ducts so that each main room has several hot air vents scattered around the edge, and one cold air return. Switch on the new heat pump and run the start-up tests recommended by the manufacturer.