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Geothermal Heat Pumps Vs. Air Source Heat Pumps: Which Is Better?

Geothermal Heat Pumps Vs. Air Source Heat Pumps: Which Is Better?

How to Choose Between Geothermal & Air Source Heat Pumps

If you’re deciding between an air source heat pump vs. a ground source heat pump, we’ve got good news: Either way, you’re making a great investment. 

Heat pump technology is significantly more efficient than conventional heating, venting, and air conditioning (HVAC). By moving heat from one space to another, heat pumps eliminate the need for fossil fuel combustion, which means cleaner air, improved comfort, and much lower energy use—reducing energy bills compared to inefficient heating and cooling systems. 

BlocPower specializes in air source heat pump (ASHP) system design and installation, but we’re also advocates of ground source (also known as geothermal) systems. Below, we’ll discuss the functionality of ground source vs air source heat pumps and explain the benefits of each option. 

If you’re interested in affordably upgrading to a modern heating and cooling system, BlocPower can help. Answer a few questions about your building to get started.

Geothermal Heat Pumps Vs. Air Source Heat Pumps: An Overview

In the United States, most homes have combustion furnaces. These HVAC systems generate heat to create warm air, then force that hot air through ductwork. It’s a reliable process, but it’s not especially efficient: An older furnace might have an annual fuel utilization efficiency of 56% to 70%, which means that it wastes 30-44% of the heat it generates.

Heat pumps don’t actively generate heat. Instead, they use a refrigerant to collect and transfer heat energy. An air source heat pump accomplishes this by drawing heat from ambient air, using a process similar to a standard air conditioner. 

Unlike air conditioners, air source heat pumps have a reversing valve that allows them to provide both heating and cooling. For a more detailed overview of how air source heating works, read: What Is An Air Source Heat Pump (ASHP)? Your Go-To Guide.

Ground source heat pumps use the same basic process, but the heat source and heat sink is—you guessed it—the ground.  Below the frost line (the depth beneath the ground level at which groundwater freezes), the ground maintains a stable temperature year-round that doesn’t fluctuate with outdoor air conditions. 

By transferring energy from the ground versus drawing energy from outdoor air, geothermal systems can provide low-cost heating and cooling throughout the year—and due to the small delta in temperature with the building’s interior, they don’t lose much efficiency during extreme weather.

Air Source Heat Pumps Vs. Ground Source Heat Pumps: Which retrofit makes sense?

From an operational perspective, the primary difference between ground source and air source heat pumps is efficiency. Since geothermal pumps collect and transfer heat from the earth, they draw less electricity than air source heat pumps when operating.

However, geothermal heat pumps have some practical disadvantages:

  • Geothermal heat pump installation is expensive and disruptive. Horizontal geothermal heat pumps require a large area of piping installed below the frost line, which is several feet below ground level. Vertical systems require boreholes drilled several hundred feet in the ground; the machinery needed to drill those holes requires access from the street as well as vertical clearance to operate. Of course, heavy digging means high labor costs. Energy incentive programs can make the investment more affordable, but geothermal systems are easily twice as expensive than air source heat pumps. .
  • Soil properties and characteristics are important.  Those with high thermal conductivity and low resistivity are preferable. A geological survey would determine those parameters. Note that drilling through rock like granite would be cost prohibitive.
  • Some cities may refuse permitting. Obtaining the necessary permits for digging can be difficult or impossible, particularly if the project would disrupt sidewalks or other shared spaces. In urban areas, street closing may be required, which could be a deal breaker.
  • Ground source heat pumps may not provide the same flexibility. A mini-split, multi-split, or variable refrigerant flow (VRF) air source heat pump system can deliver air directly to a room, allowing tenants to control the temperature in their own space. Ground source heat pumps typically use an air handler and ductwork to force hot or cold air throughout the building via air registers. This isn’t always the case—some manufacturers offer ground source systems with wall units that have individual thermostats—but generally, consumers have more flexibility with air source heat pumps. In some cases, a geothermal system can provide low-temperature hot water to heat a space. 

BlocPower can help you find the right heat pump system for your property.

The takeaway: In most cities, air source heat pumps are a better choice. However, if you’re upgrading from a conventional HVAC system to an air source or ground source heat pump—regardless of which technology you choose—you’ll be using a lot less energy. 

With the price of gas and oil rising much faster than electricity, it is also a great time to switch to electric heating and cooling. 

If you’re researching an HVAC upgrade, BlocPower can help you take the next steps. From design to installation, we provide a streamlined process for switching to Energy Star rated air source heat pump systems. 

Our Energy Service Agreements (ESAs) allow building owners to retrofit while keeping their budgets intact, and on average, BlocPower customers save 20-40% on their heating and cooling bills compared to inefficient HVAC systems.

Complete this brief survey to get a free assessment of your home or building’s suitability for air source heat pumps.

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