Five ways to bury a loop
"Geothermal" is really just the umbrella term — the loop configuration underneath it determines the cost, the land you need, and which one wins for a given house: lot size, soil, water access, and local permitting, not a universal "best" loop (DOE, Guide to Geothermal Heat Pumps; Carrier).
| Loop type | Installed cost | Best fit for your lot |
|---|
| Open-loop (well)Pumps groundwater through the unit, then discharges it — no antifreeze loop, often cheapest. |
|
Rural properties with a reliable, permittable well (4–8 GPM) |
| Pond / lake loopCoiled pipe submerged 8+ ft in a pond/lake (≥½ acre, 8–10 ft deep) within ~300 ft of the house. |
|
Rural or lakefront lots with a suitable water body already on-site |
| Horizontal closed-loopPipe in trenches 4–6 ft deep, ~400–600 ft of trench per ton (1,200–1,800 ft for a 3-ton home). |
|
New construction or larger lots (½ acre+) with diggable soil |
| Vertical closed-loopU-bend pipe in boreholes 150–300+ ft deep, ~20 ft apart — small footprint, higher cost per foot. |
|
Small or tight lots, shallow/rocky soil, or an untouched yard |
| Direct exchange (DX)Refrigerant runs directly through buried copper tubing — no water/antifreeze loop or pump. |
Rarely quoted — too few specialty contractors nationally for a typical range |
Areas with a specialty DX contractor; treat as regional, not a default choice |
Cost is loop only — excludes the indoor unit and ductwork. Hard rock, difficult access, or long trench runs push toward the top of each range. Sources: Carrier, Geothermal Insider.
How the flagship units compare
Every major manufacturer sells a "flagship" ground-source line the same way they sell a flagship air-source unit — and just like air-source, the spread between brands is real. The table below compares the top-tier residential unit from four manufacturers on EER (Energy Efficiency Ratio — cooling output per unit of electricity, on a fixed hot-day test) and COP (Coefficient of Performance — units of heat delivered per unit of electricity consumed). Higher is better on both.
| Flagship model | Cooling — EER | Heating — COP |
|---|
| WaterFurnace7 Series (700A11) |
|
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| ClimateMasterTrilogy 45 (QE) |
|
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| BoschGreensource CDi (SM048) |
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| GeoComfortVS/VT Series |
|
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Two things worth knowing before comparing these to a standard central AC or furnace: an 18–22 EER geothermal unit in cooling mode is already well ahead of a good standard central air conditioner (SEER 16 or so), and most flagship geothermal units offer an optional desuperheater — a small add-on heat exchanger that captures waste heat the system would otherwise dump into the ground and routes it to preheat your domestic hot water, essentially free, on top of whatever space heating and cooling savings the unit already delivers (Geothermal Insider, on desuperheaters).
Where the economics actually work
Read this before you run any payback math. The 30% federal tax credit for residential geothermal (IRC §25D) ended for good — it does not apply to any system placed in service after December 31, 2025, with no phase-down and no replacement (
IRS, Residential Clean Energy Credit). The One Big Beautiful Bill Act, signed July 4, 2025, repealed it outright, so the roughly $8,000–$10,000 that credit used to knock off a typical project is simply gone for any 2026-or-later install (
Congressional Research Service, on the credit's expiration). Every payback figure below assumes no federal credit — check
Utility and State Programs for what your state or utility still offers, since those haven't necessarily disappeared with the federal credit.
With that credit gone, geothermal's payback period now depends almost entirely on two things: what you're replacing, and your local electricity and fuel prices. Ranked best to worst payback, based on current no-federal-credit modeling for a retrofit install:
1Replacing an oil or propane furnace8–15 yrs
2New construction (lower incremental cost)8–18 yrs
3Replacing electric resistance or an aging heat pump8–18 yrs
4Replacing natural gas (expensive market, >$1.50/therm)18–27 yrs
5Replacing natural gas (cheap market, <$1.00/therm)30–60+ yrs
At sub-$1.00/therm gas, geothermal essentially never pays back within a system's service life, and it isn't the right call financially there. Source: Geothermal Insider, payback-period modeling.
New construction vs. retrofit
Lower cost
New construction
- Loop timing: Before landscaping or driveway goes in
- Why cheaper: Open yard access, no demolition
VS
+30–60% cost
Retrofit (existing home)
- Loop timing: Trenched or drilled around existing structures
- Why pricier: Yard access, ductwork, demolition
Installing the loop while the lot is still bare ground can run 15–50% less than adding one to an already-landscaped, already-built home, depending on loop type — this is the single biggest lever in geothermal economics. Trenching or drilling around an existing driveway, septic field, mature landscaping, and utility lines is what drives the retrofit premium. Sources: Geothermal Insider, new construction; Geothermal Insider, existing homes.
Climate zone still matters — just differently than for air-source
A standard air-source heat pump's efficiency falls as the outdoor temperature drops, which is why our Chicago case study found even a top cold-climate model losing ground to gas heat on the coldest days. Geothermal mostly sidesteps that problem — because the ground stays a stable 45–75°F year-round no matter how cold or hot it gets outside, a ground-source unit's heating COP typically holds in the 3.0–4.0 range through the entire winter, without the sharp capacity and efficiency drop-off an air-source unit shows at 5°F or below (DOE, Guide to Geothermal Heat Pumps). That stability is exactly why the coldest and hottest climates tend to be where geothermal's efficiency edge over air-source is largest in absolute terms — even though, per the payback chart above, the fuel it's replacing and your local electricity rate still decide whether that edge is worth the higher installed cost.