Geothermal vs Air Source Heat Pumps
Updated 2026-08-16 · 7 min read
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Both move heat rather than creating it. The difference is where they get it from, and that single choice drives everything else.
How does geothermal differ from an air source heat pump?
Air source exchanges heat with outdoor air. Air temperature swings widely — from below 0°F to over 100°F — and the heat pump's performance swings with it. When you need heat most, there's least available.
Ground source (geothermal) exchanges heat with the earth, through a buried loop of fluid. A few feet down, ground temperature stays roughly in the 45–70°F range year-round depending on region and depth. That stability is the whole advantage.
The heat pump itself works the same way. Only the heat exchanger location changes.
What stability buys
Capacity that doesn't collapse. An air-source unit at 5°F is fighting for heat that isn't there. A ground-source unit at 5°F outdoor air is still exchanging with 50°F earth, so it delivers essentially full capacity.
Higher efficiency, consistently. Ground-source COPs typically run higher than air-source across the season, and the gap widens in extreme weather.
Little or no backup heat. This matters more than it sounds. Without a large electric strip heater, the electrical load drops substantially — which can be the difference between needing a service upgrade and not. See heat pump backup heat explained.
No defrost cycles. There's no outdoor coil to frost. See heat pump defrost cycle.
No outdoor unit. Nothing to look at, nothing to hear, nothing exposed to weather. Equipment life is correspondingly longer.
Why does geothermal cost so much more?
This is the entire economic question, and it's site-specific rather than a catalog price.
Horizontal loops. Trenches a few feet down, over a substantial area. Cheapest to install where you have the land — and you need real land, plus the willingness to have it excavated.
Vertical loops. Boreholes drilled deep, taking little surface area. Suits small lots. Cost depends on local geology, required depth, and whether a drilling rig can access the site. Rock is slower and more expensive than soil.
Pond or lake loops. Coils submerged in a body of water on your property. Cheapest of all when available, which is rarely.
Open loop. Uses groundwater directly from a well and discharges it. Efficient, cheapest to install, but requires adequate water quality and quantity, and it's regulated — many jurisdictions restrict or prohibit it.
The variables that matter most: available land, geology, drilling access, and local regulation. Two neighboring properties can quote very differently.
Why the gap has narrowed
Geothermal's strongest historical argument was cold-weather performance — air-source units used to collapse below freezing and lean heavily on strip heat.
Modern cold-climate air-source equipment, with variable-speed inverter compressors and vapor injection, maintains 75–90% of rated capacity at 5°F and keeps producing heat well below 0°F.
That doesn't make geothermal worse. It makes the marginal benefit smaller, while the loop field cost has stayed high. In much of the country, a cold-climate air-source system now captures most of the available benefit for a fraction of the installed cost.
Side by side
| Air source | Ground source | |
|---|---|---|
| Heat exchange with | Outdoor air | The earth |
| Capacity at 5°F | 40–90%, depending on tier | Essentially full |
| Seasonal efficiency | Good to very good | Best |
| Backup heat needed | Usually some | Little or none |
| Defrost cycles | Yes | No |
| Outdoor equipment | Yes | None |
| Installation disruption | Low | High — excavation or drilling |
| Site requirements | Space for one unit | Land, geology, drilling access |
| Equipment life | ~15 years | ~20–25 years indoor; loop 50+ |
| Installed cost | Moderate | High, site-dependent |
When is geothermal worth it?
- New construction, where excavation is already happening and the loop can go in before landscaping
- You have suitable land and favorable geology
- Very cold climate with a long heating season, so the efficiency advantage accumulates over many hours
- Expensive electricity, which magnifies the value of every efficiency point
- Long time horizon. The loop lasts decades and outlives multiple heat pumps — but only if you're there to benefit
- Electrical constraints. No strip heat means a smaller service requirement
When is an air source heat pump the better choice?
- Retrofit into an existing home where excavation is disruptive or impossible
- Small lot, difficult access, or rock
- Mild to moderate climate, where the seasonal advantage is small
- Shorter time horizon — you may move before the payback lands
- Budget constraints. A cold-climate air-source system installed well beats a geothermal system you don't buy
The honest framing
Geothermal is the better machine. It is not always the better purchase.
The loop field is a large, site-specific, mostly irreversible investment. Where the site is favorable and the climate is harsh, it's excellent. Where drilling is expensive or the climate is moderate, a good cold-climate air-source system installed properly is usually the better use of the same money — and installation quality matters more to your actual bill than the choice between these two technologies.
Run the comparison for your own rates and climate with the heat pump payback calculator.
Where to go next
More in our heating and cooling guides.
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