Should You Use an Air-Source or a Ground-Source Heat Pump?

One attractive option for both heating and cooling a home is a heat pump. The most common heat pump used in a home is called an air-source heat pump. It looks almost identical to an AC unit. There is also a second, more efficient option that you might be able to use in your home. A ground-source heat pump is more costly to install than an air-source heat pump, but it may offer you greater value in the long run. 

Air-Source Heat Pumps

A heat pump evaporates a refrigerant in the coils outside your home to extract heat from the air. The pump then condenses the refrigerant in the coils inside your home to release the heat in the refrigerant and warm your home. This is the exact opposite of how an air conditioner works, so with a reversal of the function of the coils, a heat pump can both heat and cool your home. The problem with air-source heat pumps is that they are subject to the unstable nature of outside air temperatures. The hotter it is outside, the harder it is for your heat pump to push heat into the air as it labors to cool your home. The colder it gets outside, the harder it is for your unit to extract heat from the air to use in heating your home. Thus, the more extreme the temperature is outside, the less efficient your unit is. 

Ground-Source Heat Pumps

Seeking to avoid the variable nature of air temperatures, heat-pump designers have created coils that can be buried underground. At a depth of even five feet down, the temperature of the earth stays between 50–60 degrees year round. These moderate temperatures allow a ground-source heat pump to reach efficiency levels of up to 600% as opposed to the 250% efficiency level of an air-source heat pump on a cool day. 

When you are deciding whether you should use an air-source heat pump or a ground-source heat pump, two factors should govern your choice:

1) Financing costs—Because of the need to excavate, a ground-source heat pump will come with a much higher price tag than an air-source heat pump. However, as long as your financing costs are less than the amount of money you stand to save by reducing your cooling costs, a ground-source heat pump can still be more the economical choice.

2) Climate—If you live in the north or in a mountainous region, it may get too cold to use an air-source heat pump. Thus, you will either have to use a furnace, which creates its own heat, or a ground-source heat pump, which will not be affected by plummeting air temperatures. 

If you are thinking about using a ground-source heat pump in your home, talk to an HVAC technician about whether this makes sense for you.