There are numerous types of heat pump systems.
You can get a water source heat pump, geothermal heat pump or an air source heat pump.
A water based heat pump is basically how it sounds. You need it installed by a body of water in order to run. A geothermal heat pump has the outdoor air compressor buried underground to access the heat hot & cold temperatures. Think of in the wintertime how chilly the air is. The air under the soil is undoubtedly quite a bit warmer, the same is true for summer time cooling. Access to the ground temperature is quite smart & undoubtedly efficient. The replacement of this system is undoubtedly costly since you need to dig a trench in order to install the equipment. An air source heat pump has the indoor air handler standing in your grass & using the existing heat energy around you. No, it is not as efficient as the other numerous options, but it is better than a gas furnace system. Using heat energy rather than creating it saves you money & ensures cleaner air. You are using the outdoor air quality rather than recycling the same, stale air inside. Your indoor air conditions has less dust, pet dander & debris in it this way. The expense of a heat pump system, no matter what system is quite fancy. You need either a horizontal or vertical loop system installed in the process & it is not easy. Once the heat pump is installed & operational, you should save enough money for it to spend money back itself.