A heat pump is a great choice for heating a home because it runs off electricity. Thus, if you use a wind turbine or solar panels, you can take temperature conditioning completely off the grid. On the other hand, an air-source heat pump is subject to the highly variable nature of air temperatures. Thus, it is inefficient when the outside temperature are extremely hot or extremely cold. This is where a ground-source heat pump has an advantage.
How a Heat Pump Works
Unlike furnaces, heat pumps do not create their own heat. Instead, they absorb heat from one location and then expel it in another location. For example, an air-source heat pump absorbs heat from the outside air and then expels that heat inside your home to heat it up. While you might not think this works when air temperatures fall, even when air temperatures are at or around freezing, a heat pump can still pull some heat out of the air. On the other hand, they have to work very hard to do so. Air-source heat pumps work best for moderate climates because they are inefficient at extracting heat from cold temperatures.
How a Ground-Source Heat Pump Is Better
A ground-source heat pump seeks to improves on the limitations of an air-source heat pump by placing a specially designed set of coils underground. How is this advantageous? Ground temperatures are both more moderate and more consistent than air temperatures. In fact, at twenty feet deep, air temperatures will stay between 50-60 degrees year round. Thus, no matter how hot or how cold it gets outside, your heat pump can still extract heat from the relatively stable and moderate ground temperatures. In this way a ground-source heat pump can reach efficiency levels of up to 600% as compared to air-source heat pumps which only reach up to 275% efficient.
If you are looking for a heating and cooling unit that runs off electricity, then a ground-source heat pump will give you a lot of bang for your money, moving six units of heat for every unit of electricity that it uses. On the other hand, the cost of burying your ground-source coils twenty feet below the surface of the ground drives the price of a ground-source model way up. If you have the money to afford the excavation costs, then the ground-source model is the way to go, but if you don't have the budget for excavation then you will need to use an air-source that pump to provide at least three seasons of comfort.