An air-source heat pump costs $5,800–$10,000 installed, operates at COP 2.5–4.5, and lasts 15–20 years. A ground-source (geothermal) heat pump costs $18,000–$35,000 installed, operates at COP 3.5–5.0 year-round regardless of outdoor temperature, and lasts 20–25 years (with a ground loop lasting 50+ years). Both are far more efficient than gas furnaces, but they serve different homeowner needs.
The short answer: choose air-source if you want lower upfront cost and faster payback. Choose ground-source if you're building new, planning to stay 15+ years, want maximum efficiency, or live in a climate with extreme temperature swings.
Head-to-Head Comparison
| Feature | Air-Source Heat Pump | Ground-Source (Geothermal) |
|---|---|---|
| Installed cost (3-ton) | $5,800–$10,000 | $18,000–$35,000 |
| After federal tax credits | $3,800–$8,000 | $12,600–$24,500 |
| Heating COP (47 °F outdoor) | 3.5–4.5 | 3.8–5.0 |
| Heating COP (0 °F outdoor) | 1.5–2.5 | 3.5–4.5 (unaffected) |
| Cooling EER | 10–14 | 14–20 |
| Annual operating cost* | $742–$1,078 | $480–$720 |
| Annual savings vs gas* | $200–$600 | $560–$1,000 |
| Equipment lifespan | 15–20 years | 20–25 years |
| Ground loop lifespan | N/A | 50+ years |
| Maintenance cost/year | $80–$200 | $50–$150 |
| Outdoor noise | 55–65 dB | Near silent (indoor unit only) |
| Visual impact | Outdoor unit visible | No outdoor unit (all underground) |
| Property requirements | Outdoor pad space | Yard for loops or drill rig access |
| Best for | Most homeowners, retrofits | New builds, long-term stays, extreme climates |
Zone 4, 2,000 sq ft, $0.14/kWh electricity, $1.30/therm gas.
How Each System Works
Air-Source
An air-source heat pump exchanges heat between the indoor air and the outdoor air using a refrigerant cycle. The outdoor unit absorbs heat from outdoor air in winter (even cold air) and rejects heat to outdoor air in summer. Since outdoor air temperature varies from −15 °F to 115 °F+ depending on your location and season, the system's efficiency varies with conditions.
Ground-Source (Geothermal)
A ground-source heat pump exchanges heat with the earth instead of the air. Buried pipes (the "ground loop") circulate a water-antifreeze solution underground, where the temperature remains stable at 45–65 °F year-round (depending on latitude and depth). This stable temperature source is the geothermal system's key advantage — it doesn't matter if it's −20 °F or 105 °F outside; the ground loop provides a consistent, moderate-temperature heat exchange medium.
There are three main loop configurations. A horizontal loop uses trenches 4–6 feet deep across 400–600 linear feet per ton — requiring a large, flat yard. A vertical loop drills boreholes 150–200 feet deep per ton — works in smaller yards. An open loop pumps groundwater directly through the heat exchanger, requiring an adequate well and a discharge point (like a return well or pond).
Why Geothermal Is More Efficient: An air-source heat pump at 0 °F must extract heat from air that's 70 degrees colder than your indoor target. A geothermal system extracts heat from the ground at 50 °F — only 20 degrees colder. Less temperature difference means less compressor work, which means higher COP.
Efficiency Comparison by Temperature
The efficiency gap between air-source and ground-source grows as outdoor conditions become more extreme.
| Outdoor Temp | Air-Source COP | Cold-Climate Air-Source COP | Ground-Source COP | Ground-Source Advantage |
|---|---|---|---|---|
| 95 °F (cooling) | 2.5–3.5 (EER) | 2.5–3.5 | 4.0–5.5 (EER) | +40–60% |
| 47 °F | 3.5–4.5 | 4.0–5.0 | 3.8–5.0 | +0–10% |
| 35 °F | 3.0–3.8 | 3.2–4.0 | 3.8–5.0 | +25–30% |
| 17 °F | 2.0–2.8 | 2.5–3.5 | 3.8–5.0 | +40–80% |
| 5 °F | 1.5–2.2 | 2.0–3.0 | 3.8–5.0 | +65–130% |
| 0 °F | 1.2–1.8 | 1.8–2.5 | 3.8–5.0 | +90–180% |
| -15 °F | Off or 1.0 | 1.2–1.5 | 3.8–5.0 | +250–400% |
The ground-source system is most advantageous in extreme climates — both very cold winters and very hot summers. In mild climates (zone 3–4), the efficiency advantage exists but is smaller, making the payback period on the higher upfront cost longer.
Cost Comparison: Install + Operating + Lifetime
| Cost Category | Air-Source | Cold-Climate Air-Source | Ground-Source |
|---|---|---|---|
| Equipment cost | $2,800–$5,500 | $4,500–$7,000 | $5,000–$8,000 |
| Installation cost | $3,000–$4,500 | $3,500–$5,000 | $13,000–$27,000 |
| Total installed | $5,800–$10,000 | $8,000–$12,000 | $18,000–$35,000 |
| Federal tax credit (2026) | $0 (25C EXPIRED Dec 31, 2025) | $0 (25C EXPIRED Dec 31, 2025) | $0 (25D EXPIRED Dec 31, 2025) |
| Net installed (2026, no state/IRA) | $5,800–$10,000 | $8,000–$12,000 | $18,000–$35,000 |
| Annual operating cost | $882 | $780 | $520 |
| Annual maintenance | $150 | $150 | $100 |
| 15-year operating total | $15,480 | $13,950 | $9,300 |
| 15-year total ownership (2026) | $21,280–$25,480 | $21,950–$25,950 | $27,300–$44,300 |
| 25-year total ownership* | $29,980–$34,180 | $28,450–$32,450 | $28,400–$40,300 |
| 30-year total ownership** | $39,680–$43,880 | $37,900–$41,900 | $34,700–$46,100 |
*25-year comparison assumes one air-source replacement at year 17 ($6,000–$8,000) but geothermal equipment still running. **30-year comparison assumes two air-source replacements but only one geothermal equipment replacement (ground loop still original).
Installation Requirements
| Requirement | Air-Source | Ground-Source |
|---|---|---|
| Outdoor space | 4×4 ft pad for outdoor unit | Large yard (horizontal) or drill access (vertical) |
| Indoor space | Air handler closet/utility room | Similar — slightly larger indoor unit |
| Electrical | 30–50A 240V circuit | 30–50A 240V circuit |
| Ductwork | Uses existing or add new | Uses existing or add new |
| Permits | HVAC permit | HVAC + drilling/excavation permit |
| Installation time | 1–2 days | 1–2 weeks |
| Disruption | Minimal | Significant (trenching/drilling yard) |
| HOA concerns | Outdoor unit visible | None after install (all underground) |
| Property restoration | None | Yard re-grading and re-seeding |
The biggest barrier to geothermal is the ground loop installation. Horizontal loops require 400–600 feet of trench per ton (1,200–1,800 feet for a 3-ton system) at 4–6 feet deep, which means tearing up a significant portion of your yard. Vertical loops require a drilling rig and boreholes 150–200 feet deep per ton. In both cases, the yard will need restoration after installation.
For new construction, loop installation is far less expensive because the excavation equipment is already on-site and the yard hasn't been landscaped yet. This is why geothermal is most commonly recommended for new builds.
Climate Performance
| Climate Zone | Air-Source Performance | Geothermal Performance | Recommended System |
|---|---|---|---|
| Zone 1–2 (Hot) | Excellent cooling, minimal heating needed | Excellent, but low heating savings | Air-source (geothermal ROI too long) |
| Zone 3 (Warm) | Very good year-round | Very good, moderate advantage | Air-source (unless new build) |
| Zone 4 (Mixed) | Good year-round | Good, growing advantage in winter | Air-source (geothermal for new build) |
| Zone 5 (Cool) | Good; cold-climate model needed | Excellent, strong winter advantage | Either (geothermal if staying 15+ years) |
| Zone 6 (Cold) | Good with cold-climate model | Excellent, major winter advantage | Geothermal if budget allows; else cold-climate AS |
| Zone 7 (Very Cold) | Requires cold-climate model + backup | Excellent regardless of temps | Geothermal ideal; cold-climate AS + dual-fuel |
Lifespan and Maintenance
Geothermal systems win on longevity. The indoor heat pump equipment lasts 20–25 years, and the ground loop itself has a lifespan exceeding 50 years (some installed in the 1970s are still functioning). Air-source heat pumps last 15–20 years.
Geothermal maintenance is also simpler and cheaper. There's no outdoor unit to maintain, no defrost cycles, no outdoor coil to clean, and no exposure to weather or debris. Annual maintenance focuses on checking the circulating pump, verifying antifreeze concentration in the ground loop, and standard indoor coil/filter service. Typical cost: $50–$150 per year versus $80–$200 for air-source.
Tax Credits and Incentives
| Feature | Air-Source (25C — EXPIRED) | Ground-Source (25D — EXPIRED) |
|---|---|---|
| Pre-expiration credit rate | 30% | 30% |
| Pre-expiration maximum | $2,000/year | No cap |
| $30,000 system credit (pre-2026) | $2,000 | $9,000 |
| Status for installs after Dec 31, 2025 | EXPIRED under OBBBA | EXPIRED under OBBBA |
| Carryforward of unused pre-2026 credit | Not allowed | Allowed |
| Active 2026 pathways | State/utility + IRA HEAR or HOMES | State/utility + IRA HOMES |
Both Section 25C (air-source) and Section 25D (ground-source) credits expired for property placed in service after Dec 31, 2025 under the OBBBA (PL 119-21, signed July 4, 2025). 25D allows carryforward of an unused pre-2026 credit; 25C does not. For 2026 installs, state and utility rebates plus IRA HEAR (income-qualified, up to $8,000 for heat pumps) and HOMES (open to all incomes, performance-based) are the active federal/state pathways. (Sources: IRS OBBB FAQ; Congress.gov CRS IN12611.)
The uncapped 25D credit was a major financial advantage for geothermal through Dec 31, 2025 — a $30,000 geothermal system earned a $9,000 credit, while a $10,000 air-source system was capped at $2,000. Both 25C and 25D expired for property placed in service after Dec 31, 2025 under the OBBBA; for 2024/2025 installs that didn't claim the credit at the time, an amended return on IRS Form 1040-X may still recapture it (25D allows carryforward of an unused pre-2026 credit; 25C does not). For 2026 installs, state incentives (many states still offer additional geothermal rebates of $1,000–$5,000) plus IRA HOMES (open to all incomes, performance-based) remain the active pathways and continue to narrow the effective cost gap.
Key Takeaways
Air-source heat pumps cost $5,800–$10,000 installed; ground-source costs $18,000–$35,000. After tax credits, the gap narrows to roughly $3,800–$8,000 vs. $12,600–$24,500. Ground-source operates at COP 3.5–5.0 year-round, unaffected by outdoor temperature — a huge advantage in zones 5–7. Air-source with cold-climate technology closes much of the efficiency gap at moderate cost. Ground-source equipment lasts 20–25 years with a 50+ year ground loop, versus 15–20 years for air-source. For most existing homes, air-source offers better ROI (faster payback). For new construction, homes in extreme climates, or 15+ year stays, geothermal is the superior long-term investment.
Frequently Asked Questions
Yes, but it's more expensive and disruptive than new construction. The ground loop installation requires trenching or drilling, which means significant yard disruption. Vertical bore loops minimize yard impact but cost more. The indoor equipment installation is similar to air-source. Total installed cost for retrofit is typically $22,000–$35,000 for a 3-ton system.