Geothermal Heat Pump Systems Reference

Why this reference exists

Geothermal heat pumps (ground-source heat pumps, GSHP) are the most efficient HVAC technology available for residential use. Year-round COP 3.5-5.5 vs air-source 1.5-4.0. The federal 25D credit no longer applies: the 30-percent, no-cap credit that used to cover the loop, the drilling, the equipment and the labor ran through expenditures made on or before December 31, 2025. Quote geothermal on operating cost and on state and utility money now, and check the IRA credits reference before you put any federal number in front of a customer. The U.S. installed base is small but growing. Crews adding geothermal as a service line earn premium margins + lifetime customer relationships. This is the working overview for techs evaluating + servicing GSHP systems.

How they work

Same vapor-compression cycle as an air-source heat pump, but the heat exchanger uses the ground (50-55°F year-round at 6+ ft depth) instead of outdoor air.

In winter: ground is warmer than outdoor air → heat pump extracts heat more efficiently than air-source.

In summer: ground is cooler than outdoor air → heat pump rejects heat more efficiently.

Result: 50-80% energy reduction vs traditional gas + electric resistance; 25-50% vs air-source heat pump.

Loop types

The ground loop is the single biggest cost + design decision.

Horizontal closed loop:

• Trenches 4-6 ft deep, 150-300 ft per ton
• Best for properties with adequate yard space
• Excavator install; 1-3 days
• Least expensive loop type when yard space allows it
• Lifespan 50+ years

Vertical closed loop:

• Boreholes 150-400 ft deep, 1 borehole per ton typical
• Used on small lots; minimal surface disturbance
• Drilling rig; 2-4 days
• Most expensive loop type due to drilling cost
• Lifespan 50+ years

Pond loop:

• Coils submerged in pond 8+ ft deep
• Cheapest IF a pond exists; impractical to dig
• Requires pond owner permission + sometimes permit

Open loop / pump-and-dump:

• Pumps groundwater from one well, runs through heat exchanger, returns to another well or surface discharge
• Most efficient + cheapest IF groundwater available
• Restricted in many regions (water rights, regulation)
• Risk: well failure, fouling

Standing column well:

• Single well that recirculates groundwater within the same well
• Hybrid of closed + open
• Less common; works in fractured-rock geology

Indoor unit

The heat pump itself is similar to an air-source unit but sized for ground-side temperatures + integrated with a circulator pump for the ground loop. Common brands: WaterFurnace, ClimateMaster, Bosch, Carrier, Trane.

Components inside:

• Compressor
• Refrigerant-to-water heat exchanger (replaces outdoor coil)
• Refrigerant-to-air heat exchanger (indoor blower coil)
• Reversing valve (heat pump function)
• Circulator pump for ground loop
• Filter on ground loop
• Expansion tank
• Air handler + ducts (or hydronic distribution)

Sizing

Same Manual J load calc as any HVAC system. Geothermal is sized for HEATING load (highest demand) typically - cooling is usually fine on heating-sized system.

Typical residential:

• 1,500 sq ft: 2-3 tons
• 2,500 sq ft: 3-4 tons
• 4,000 sq ft: 4-6 tons

Each ton = 12,000 BTU/hr nominal. Required ground loop:

• Horizontal: 150-300 ft of trench loop per ton (200 ft typical)
• Vertical: 150-400 ft of bore per ton, one borehole per ton typical. Formation conductivity decides where in that range you land, so this is a design output, not a rule of thumb to quote from

Soil type affects loop length:

• Wet clay (high conductivity): shorter loops
• Dry sandy soil: longer loops
• Rocky: drilling more expensive but conductive

A formal loop design is required - the loop length is part of the system performance. Improperly sized loop = poor performance + customer dissatisfaction.

Tax credit + incentives

Federal 25D is gone for new work. It gave 30% of total cost including loop, heat pump and install, with no cap, and it applied to expenditures through December 31, 2025 only. Do not quote it on a job going in today. It still matters in two narrow ways: a customer who paid in 2024 or 2025 may be carrying the credit forward on their return and will call you for the AHRI certificate, and any older proposal still sitting in your pipeline with a 30-percent line on it has to be repriced before it goes back out. See the IRA credits reference for the full timeline.

State and utility money is now the whole incentive story, and it varies far more by address than the federal credit did. Verify the current program terms before quoting; these move every budget cycle:

• New York NY-Sun + utility programs: incentive
• Massachusetts MassSave: heat pump rebates
• Maryland: residential clean energy rebate
• Many utility programs: rebate for geothermal

Without the federal credit the net out-of-pocket no longer lands anywhere near a premium air-source install on most jobs. Build the number from the state and utility programs that actually apply at that address and show it honestly; the case for geothermal now rests on operating cost and loop lifespan, not on a rebate that closes the gap for you.

Operating economics

Annual heating + cooling cost for typical 2,500 sq ft home, ranked highest to lowest:

• Gas furnace + standard AC: highest annual operating cost of the three
• Air-source heat pump: meaningfully lower than gas + AC
• Geothermal heat pump: lowest of the three, roughly half of gas + AC

Savings vs gas + AC compound year over year. Payback runs long, and it runs longer now that the federal credit is gone, so compute it from that customer's actual bills and their actual net cost rather than quoting a generic window. The loop outlives the payback either way at 50+ years.

Property value lift: geothermal-equipped homes sell at 3-7% premium in markets aware of the tech.

When to recommend geothermal

Strong candidates:

• Yard space for horizontal loop, or drilling feasible
• High heating + cooling load (large home, cold climate)
• Customer staying in home 10+ years
• Concerned about energy costs + carbon
• Existing failing HVAC needing replacement (cost-difference smaller in replacement vs add-on)
• Budget for upfront investment (financing helps close the gap when the customer has none)

Weak candidates:

• Small lot with rocky soil + no drilling possible
• Customer planning to move in 3-5 years
• Low energy bills already (mild climate, small home)

Service + maintenance

Annual maintenance similar to air-source but with additional loop checks:

• Refrigerant charge + temperatures
• Air filter
• Circulator pump operation
• Loop pressure (typically 30-50 psi)
• Loop antifreeze concentration (closed loops use 15-25% propylene glycol or methanol blend)
• Water quality test (open loops)
• Heat exchanger inspection for fouling

Annual service: priced somewhat above air-source due to extra loop work.

Common pitfalls

• Undersized loop: poor performance in extreme weather, customer fury
• Open loop in poor groundwater: clogging + scale on heat exchanger
• Mixed antifreeze chemistries: corrosion + sludge
• No purge during install: air pockets reduce flow
• Loop pressure not maintained: low pressure = poor heat transfer
• Heat pump not sized to loop: capacity limited by ground side
• Customer expectations: "geothermal heats and cools my home for free" - explain electric cost
• Forgotten ground-water permit: open loop without proper permits

Customer talking points

Closing geothermal:

1. "Most efficient heating + cooling possible: COP 3.5-5.5 year-round."
2. "Operating cost 50-70% less than gas + AC, every year, for the life of the system."
3. "Loop lifetime 50+ years; heat pump 20-25 years; nothing outdoors to rust or vandalize."
4. "Carbon impact: lowest of any heating system."
5. State and utility incentives where they exist, quoted from the current program terms for that address, never from memory.

Do NOT lead with the federal tax credit. It ended for expenditures after December 31, 2025, and a customer who hears "thirty percent back" and later finds out otherwise is a refund conversation and a review you will not recover from. The honest pitch now is the operating-cost math over the life of the loop, which is a stronger argument anyway because it does not depend on a program that can be repealed.

Drilling + excavation logistics

For ground loop install:

• Excavation crew or drilling contractor (specialized; not all HVAC crews can do)
• Coordination with HVAC install
• Permits + AHJ inspection
• Restoration of yard (sod, plantings, hardscape)
• Customer expectation management (yard work for days)

Some HVAC companies partner with drilling contractors; others handle in-house.

References

• DOE Geothermal Heat Pump Resources
• IGSHPA (International Ground Source Heat Pump Association) Standards
• AHRI/ASHRAE/ISO 13256-1 and 13256-2, performance rating for water-to-air and water-to-water ground-source heat pumps (AHRI 870 covers direct-geoexchange units only, a different machine)
• IRS Form 5695 (25D credit, for customers still carrying forward a pre-2026 claim)
• Manufacturer specs (WaterFurnace, ClimateMaster, Bosch, Carrier)
• Manuall internal: Heat Pump Sizing for Cold Climate Reference, IRA Home Energy Tax Credits: What Ended, What Survives, and What You Can Still Quote