Canary Media’s Electrified Life column shares real-world tales, tips, and insights to demystify what individuals can do to shift their homes and lives to clean electric power.
Micah Parkin wanted to quash her home’s carbon pollution to help fight climate change. So she took a familiar step among climate-inclined homeowners: She got a heat pump — just not the typical variety.
Her heat pump pulls warmth from the ground, rather than the air, and the appliance “has been doing wonderfully well,” Parkin, the executive director of grassroots climate-action group 350 Colorado, told me from her home on a snowy January day. “It’s had no problem keeping up with these zero and negative temperatures.”
Heat pumps, whatever their heat source, are critical for decarbonizing space and water heating, which accounts for more than 60% of the energy homes consume in the U.S. Switching from gas, propane, and fuel-oil systems can save homeowners money and is guaranteed to have health benefits given the toxic pollutants fossil-fuel systems emit.
Ground-source, or geothermal, heat pumps have a superpower over the much more common air-based systems: efficiency. While air-source heat pumps can perform two to three times as efficiently as fossil-fuel systems in cold weather, ground-source heat pumps can perform about twice as efficiently again. To put it in dollar terms: That means cutting the heating bill from an air-source heat pump in half.
That efficiency is what won Parkin over. She has a 7-kilowatt solar panel system on her roof, and she and her husband wanted a heat pump that would minimize their reliance on comparatively dirty grid power by staying within the budget of what their solar produces. “It was really important to us that it be the most efficient system possible to use as little electricity as possible,” she said.
But for all their efficiency gains, geothermal heat pumps have one big thing holding them back: They cost roughly double to install compared with air-source systems.
Out of 123.5 million U.S. homes, just 1.3 million — or about 1% — rely on a geothermal heat pump, according to a January report by the Department of Energy. Air-source heat pumps provide primary heat for 13% of homes and are outselling fossil-gas furnaces by a wider margin than ever.
The DOE sees ample room for geothermal heat pumps to take off though. With the right policies and investments, annual adoption of the tech could double, with the equivalent of 7 million more American homes installing geothermal heat pumps by 2035.
“In the next five or 10 years, you’re really going to see these become much more of a household name as a way to heat and cool your home,” said Timothy Steeves, report co-author and geothermal fellow at the DOE.
The benefits could be enormous not only for the homeowners involved but for the power system overall. Geothermal heat pumps are way less of a burden on the grid due to their efficiency, the report found — enough to net roughly $4 billion in annual savings on grid system costs, which could be passed on to utility customers.
Could geothermal heat pumps, with their unrivaled efficiency and grid and climate advantages, be a good fit for you? Let’s dig into the details of this clean-heating tech.
How geothermal heat pumps work
Ground-source heat pumps, also called geo-exchange, earth-coupled, and earth-energy heat pumps, are so efficient because they tap heat where it’s steady and abundant: underground.
The appliances connect to flexible plastic pipes that delve into the earth. These ground loops, laid horizontally in trenches less than 10 feet deep or vertically in boreholes 100-plus feet deep, carry a nontoxic mix of water and glycol to absorb thermal energy from the ground. That energy is then delivered indoors and transferred to refrigerant in the heat pump unit. A compressor squeezes the refrigerant gas, raising the temperature further to provide heating that can flow through ducts, mini-splits, or radiators.
Drawing heat from underground is a winning strategy because the shallow earth stays at a fairly constant temperature of somewhere between 40 and 70 degrees Fahrenheit. In the winter, it’s easier to find heat in the ground than it is in the volatile — and often chilly — air. Conversely, in the summer, the ground is cooler, making it a better heat sink.
Some geothermal heat pumps draw energy from water bodies, rather than the ground, through a similar process.
Another selling point for ground-source heat pumps is their longevity. The heat pump unit itself has a slightly better average lifespan — around 20-plus years for ground-source heat pumps compared with 15 years for air-source heat pumps, according to the DOE. But the underground infrastructure can last 50 years, potentially more, said Kathy Hannun, founder and president of Dandelion Energy, a home-geothermal company and spinout from X, Google’s “moonshot factory.”
Ground-source heat pumps can also simplify some aspects of installation, Hannun said. Dandelion designed a ground-source heat pump that doesn’t need as much electrical capacity and can produce warmer air than typical heat pumps, making it more compatible with existing ductwork, she said.
