Air-Source vs. Geothermal Heat Pumps: Cost and Performance Trade-offs in Maryland
Short answer. Both systems move heat instead of making it. An air-source heat pump trades heat with the outdoor air. A geothermal (ground-source) heat pump trades heat with the ground, which stays at a steadier temperature than the air, so it uses less energy. The catch is the ground loop: the buried piping costs far more to install than an outdoor air unit. Geothermal tends to make sense on larger lots, in new construction and for owners staying a long time. Air-source suits most suburban and city lots and tighter budgets. Heat pump installers who do both can price your actual lot, which is the only comparison that counts.
The difference is the heat source
The DOE’s consumer guide to geothermal heat pumps explains the core idea. A few feet below the surface, the ground stays at a relatively constant temperature: cooler than the air in summer and warmer than the air in winter. That gives a geothermal system a dependable heat source in winter and a heat sink in summer.
An air-source unit has to work with whatever the outdoor air offers. On the coldest nights, there is less heat to collect and a bigger temperature gap to push across, so its efficiency drops (see how heat pumps work). A geothermal unit does not see that swing.
How much more efficient
The sources put it in different ways:
- The DOE guide says geothermal systems can reduce energy consumption by 25 to 50 percent compared with air-source heat pumps, and reach efficiencies of 300 to 600 percent on the coldest winter nights.
- ENERGY STAR says its certified geothermal heat pumps use 61 percent less energy than a standard model.
- The DOE guide also notes that, compared with air-source units, geothermal systems are quieter, last longer, need little maintenance and do not depend on outdoor air temperature.
Those are general figures. Your savings depend on your house’s heating and cooling load, what fuel you are replacing and your utility rates.
Why geothermal costs more to install
The heat pump itself is a familiar piece of equipment. The expense is the ground loop that connects it to the earth. The DOE guide describes four ways to build it, and says the right one depends on climate, soil, available land and local installation costs:
| Loop type | How it works | Where it fits |
|---|---|---|
| Horizontal (closed) | Pipe in trenches at least four feet deep | Generally the most cost-effective for homes, especially new construction with enough land |
| Vertical (closed) | Pipe in drilled boreholes | Limited land, or soil too shallow for trenches; can cost more but uses less land and disturbs less of the yard |
| Pond or lake (closed) | Coils at least eight feet under the surface of a suitable water body | May be the least expensive option, but only with a water body that meets volume, depth and quality criteria |
| Open loop | Well or surface water circulates through the system and is returned | Only with an adequate supply of relatively clean water and where local groundwater discharge rules allow |
Trenching and drilling are earthwork. They do not exist in an air-source job, which is why geothermal systems carry a higher upfront price even when the equipment is similar. The DOE guide says installation costs more than an air-source system of the same capacity, and that the extra cost can be recouped through energy savings in 5 to 10 years. That payback range is a general estimate from DOE, not a quote for your house.
The DOE guide also describes a middle option: a dual-source heat pump that combines an air-source unit with a geothermal one. It is more efficient than air-source alone, less efficient than full geothermal, and costs much less to install than a geothermal-only system.
Where geothermal tends to make more sense
- New construction or major renovation. DOE calls these a particularly good fit, since loop work can be planned with other excavation.
- Larger lots with room for horizontal trenches, which avoid drilling.
- Long ownership. The ground loop is a long-lived asset, so the premium is spread over more years.
- Replacing an expensive fuel, such as propane or oil, where the operating-cost gap is largest.
Where air-source tends to make more sense
- Smaller suburban and rowhouse lots without space or access for a loop.
- Tighter budgets, since there is no earthwork.
- Uncertain plans. If you may sell in a few years, the geothermal premium is harder to recover.
- Retrofits where drilling rig access or yard disruption is a real obstacle.
- Homes without ducts, where ductless mini-split heat pumps can serve rooms or zones.
The incentive picture changed after 2025
Earlier versions of comparisons like this one, including our own, said the federal geothermal credit under Section 25D continued at 30 percent through 2032. That is no longer supported by the IRS. The IRS’s Residential Clean Energy Credit page lists geothermal heat pumps as qualified property but says the credit “is not available for any property placed in service after December 31, 2025.” For a system installed in 2026 or later, neither technology has a federal residential tax credit.
What remains is state, county and utility money. The Maryland Energy Administration’s single-family incentives page lists a first-come, first-served MEA Geothermal Rebate Program, and county geothermal tax credits in Anne Arundel County, Harford County and Prince George’s County. We have not confirmed whether each is open today, so check before you count on them. EmPOWER utility programs may also apply to either technology. See the rebate stack for the full picture.
What a fair side-by-side comparison looks like
Two quotes are only comparable when they rest on the same facts about the house. Before you weigh them, make sure both:
- Use the same heating and cooling load. Ideally one Manual J for the house, done after any sealing and insulation work you plan. A geothermal quote sized for a leaky house and an air-source quote sized for a sealed one are not comparable. See is your home ready.
- Include everything to make the system run. For geothermal, that is the loop, the earthwork, permits and yard restoration. For air-source, it is the outdoor pad or mounts, line sets, electrical work and any duct changes.
- State the backup plan. An air-source quote should say what heats the house below its balance point. A geothermal quote should say whether it includes any backup at all.
- Show operating cost at your rates, not a national average.
- List the incentives each assumes, with who files them and when.
If one installer will not put those in writing, the comparison is not finished yet.
Questions to ask an installer quoting both
- “What loop type would you use on my lot, and what does the quote include for trenching or drilling and permits?”
- “What is the projected annual operating cost of each option for my house’s calculated load, not a generic percentage?”
- “Did you size both from a Manual J load calculation?”
- “Is a dual-source system worth pricing here?”
- “Which state or county geothermal incentives apply, and who files them?”
- “If I choose air-source now, what would a later move to geothermal involve?”
How to verify this yourself
- DOE: Consumer Guide to Geothermal Heat Pumps and Energy Saver: Heat Pumps
- ENERGY STAR: Geothermal Heat Pumps and Air-Source Heat Pumps
- IRS: Residential Clean Energy Credit
Tell us if a source changes. To compare local companies that list geothermal work, see the geothermal heat pumps service page.
Sources
- https://www.energy.gov/sites/default/files/2021-08/ES-Geothermal%20heat%20pumps_080221.pdf
- https://www.energy.gov/energysaver/heat-and-cool/heat-pumps
- https://www.energystar.gov/products/geothermal_heat_pumps
- https://www.energystar.gov/products/air_source_heat_pumps
- https://www.irs.gov/credits-deductions/residential-clean-energy-credit
- https://energy.maryland.gov/Pages/SingleFamilyHomes.aspx