In This Guide
How to read the numbers on this page. The cost tables and land-area ranges below are market estimates compiled from installer quotes, not published figures from a cited authority. They vary by region and geology, and they drift with time. The figures that can be attributed to a published source — Oak Ridge National Laboratory's 2018 contractor survey, DOE's geothermal heat pump page, and ENERGY STAR's certification criteria — are marked as such in the text and listed under Sources. Everything else is an estimate.
About the ORNL survey. The most specific figures here come from ORNL/TM-2018/756, a 2018 report on cutting the cost of vertical bore ground heat exchangers. Its contractor survey — recruited through an IGSHPA online forum, the IGSHPA-certified installer mailing list and LinkedIn — received only eight responses. ORNL judged the data still useful because every respondent had more than ten years in the industry. Every ORNL figure on this page is therefore what eight experienced contractors reported in 2018, not a measurement of the market.
Quick Answer
| Factor | Horizontal | Vertical |
|---|---|---|
| Cost (3-ton) | $12,000–$22,000 | $18,000–$32,000 |
| Excavation cost per foot (ORNL survey) | About half of drilling per linear foot — a trench foot and a bore foot are not equal capacity | $5.00–$15.50/ft drilled (2018 dollars) |
| Land needed | 4,500–7,500 sq ft of open ground for 3 tons (about 0.1–0.2 acre); less with slinky coils | 675–1,200 sq ft for 3 tons (225–400 sq ft per bore, 1 bore per ton) |
| Depth | 4–6 feet | 200–400 feet, average 328 ft (ORNL survey) |
| Best for | Rural/suburban lots with open yard | Small, wooded or built-up lots where a trench field won't fit, subject to rig access and drilling permits |
| Installation time | 3–5 days (trenching, all steps) | 4–6 days (drilling, all steps) |
| Yard impact | Major disruption; grass typically back in 1 season | Minimal — small drill sites |
| Performance | Shallow pipe sees the seasonal ground-temperature swing | Steadier ground temperature at depth (DOE); no rated-efficiency advantage published (see Performance) |
| Soil dependency | High — performs best with moist, conductive soil | Lower — but rock type sets drilling cost (ORNL survey) |
Market estimates except where ORNL or DOE is named in the row.
If you have roughly 4,500–7,500 sq ft of clear, open yard (about 0.1–0.2 acre) with good soil, horizontal is the lower-cost column — $12,000–$22,000 against $18,000–$32,000 for a 3-ton system, ranges that overlap. If your lot is small, rocky, wooded, or urban, vertical is usually the closed-loop option that fits, provided the rig can reach the site and local drilling rules allow it.
How Each System Works
Both horizontal and vertical loops do the same job: circulate a water-antifreeze solution through buried pipe — commonly HDPE (high-density polyethylene), though PPI's model specification also lists PE-RT and PEX for buried loops, as our geothermal loop pipe guide covers — to exchange heat with the ground. Below the surface the ground holds a nearly constant temperature year-round. DOE puts it at "between about 50°F (10°C) and 59°F (15°C)" at about 30 feet down, which makes the earth a heat source in winter and a heat sink in summer.
Horizontal Ground Loops
Trenches are dug 4–6 feet deep across a large area of your yard. HDPE pipe is laid in the trench — either in straight runs, slinky coils (overlapping loops that pack more pipe into less trench length), or multiple layers. The trench is backfilled and the yard restored. Typical dimensions, estimates except where ORNL's survey is named:
- Pipe length: 400–600 feet per ton of capacity
- Trench depth: 4–6 feet (below frost line)
- Trench length (ORNL survey): 60–500 feet, average 275 feet
- Trench spacing: 6–10 feet between parallel runs
- Total land: 1,500–2,500 sq ft per ton (standard) or 800–1,500 sq ft per ton (slinky)
Vertical Ground Loops
A drill rig bores narrow holes straight down, a U-shaped HDPE pipe is inserted into each bore, and the hole is grouted with a thermally conductive bentonite mix. Multiple bores are connected by a horizontal header trench. ORNL's contractors reported bore diameters from 4.25 to 6 inches (the middle 50% of reported values within 4.75–5.75 in.) and bore depths of 200 to 400 feet, averaging 328 feet. The other figures below are estimates.
- Bore depth (ORNL survey): 200–400 feet per bore, average 328 ft — set by geology and system size
- Number of bores: 1 per ton — 3-ton system = 3 bores
- Bore spacing: 15–20 feet between bores
- Total surface area: 225–400 sq ft per bore (just the drill site plus header trench)
Cost Comparison
| System Size | Horizontal (Trench) | Horizontal (Slinky) | Vertical |
|---|---|---|---|
| 2-ton | $8,000–$14,000 | $9,000–$16,000 | $12,000–$22,000 |
| 3-ton (most common) | $12,000–$22,000 | $14,000–$24,000 | $18,000–$32,000 |
| 4-ton | $16,000–$28,000 | $18,000–$30,000 | $24,000–$40,000 |
| 5-ton | $20,000–$34,000 | $22,000–$36,000 | $30,000–$48,000 |
Market estimates, loop-only (trenching/drilling + pipe + grouting). A complete system adds the heat pump unit ($6,000–$12,000) and indoor installation ($4,000–$8,000), likewise estimates.
ORNL's contractors reported vertical bore loop costs of $1,600 to $4,250 per cooling ton, averaging $2,350. Those are 2018 dollars, loop only. For a 3-ton system that is roughly $4,800–$12,750, about $7,050 at the average — below the table's vertical column. The two are not directly comparable: the survey is 2018 pricing, the table a current market estimate. The same survey found slinky loops averaged only slightly more per ton than straight horizontal runs, which is why the two horizontal columns sit close together.
What Drives the Cost Difference?
- Equipment: Drilling equipment is the more expensive class. ORNL's report notes that many drill rigs in service are 10 to 30 years old, puts a 20-year-old used mud rotary rig near $200,000 and a remanufactured "short hole" rig at roughly $100,000, and says a new rotary rig can cost up to $500,000 — with price points dated between 2002 and 2017. There is no comparable trenching-equipment price in ORNL's report, so the comparison stays qualitative: the capital tied up in a rig flows through to per-project pricing.
- Time: ORNL's contractors reported drilling rates of 50–200 feet per hour, with the middle 50% of reported values at 60–150 ft/h. At those rates a 300-ft bore is roughly 2–5 hours of drilling (1.5–6 hours across the full range). That is drilling time only — rig setup, pipe insertion, grouting and moving between bores come on top, so time on site per bore is longer. Multiple bores compound it.
- Geology risk: ORNL's contractors reported drilling costs below $10 per foot in drift, shale, sandstone or limestone and above $15 per foot in granite. On three bores at the survey's 328-ft average — roughly 1,000 feet — that is a swing of roughly $5,000 or more on those thresholds, depending on what is under your lot. Horizontal trenching rarely encounters surprises below 6 feet.
- Grouting: Every vertical bore requires thermally conductive grout ($500–$1,000 per bore, estimate). Horizontal loops use native backfill at no extra cost.
Land Requirements
| System Size | Horizontal (Standard) | Horizontal (Slinky) | Vertical |
|---|---|---|---|
| 2-ton | 3,000–5,000 sq ft | 1,600–3,000 sq ft | 450–800 sq ft |
| 3-ton | 4,500–7,500 sq ft | 2,400–4,500 sq ft | 675–1,200 sq ft |
| 4-ton | 6,000–10,000 sq ft | 3,200–6,000 sq ft | 900–1,600 sq ft |
Market estimates. Vertical figures assume 1 bore per ton at 225–400 sq ft per bore.
Horizontal loops need the land to be relatively clear — no trees, no buried utilities, no septic fields, no future building plans over the loop field. You can landscape over it (grass, garden beds, shallow-rooted plants) but no structures, driveways, or deep-rooted trees.
Vertical loops need only small, clear drill sites plus a header trench route. The bores can go beside driveways, near (but not under) buildings, and in relatively tight spaces. This is why vertical is usually the configuration that fits suburban and urban lots.
Performance & Efficiency
Thermal Stability
At 4–6 feet deep, horizontal loops are affected by surface temperature changes, rain, snow cover, and seasonal soil moisture. Deeper ground is steadier: DOE's 50–59°F figure is a year-round figure at about 30 feet, and a vertical bore at 200–400 feet sits well below any seasonal swing. Vertical, then, offers greater temperature stability. It does not follow that vertical is rated more efficient: ORNL, DOE and ENERGY STAR publish no orientation-specific COP comparison, and the one efficiency floor that applies, ENERGY STAR's, is set by product configuration and loop type — closed loop versus open loop within each product type — not by horizontal or vertical orientation.
Under ENERGY STAR's criteria (effective January 1, 2012, water-to-air units tested to ISO 13256-1), a closed-loop water-to-air heat pump must reach 17.1 EER / 3.6 COP and an open-loop water-to-air unit 21.1 EER / 4.1 COP. A horizontal closed loop and a vertical closed loop are the same product type under that table.
Soil Conditions Matter More for Horizontal
- Clay-rich, moist soil: Good for horizontal — moves heat well
- Sandy, dry soil: Poor for horizontal — moves heat poorly, so the field needs more pipe and more area
- Bedrock shallower than 4 feet: Trenching is generally impractical — vertical, or a pond or open-loop system where available, is the usual route
- High water table: Usually helps thermal contact for either loop; check local groundwater rules before drilling
Vertical loops depend less on the top few feet of soil because most of the bore runs through deeper, steadier ground. What rock type does change is drilling cost: below $10 per foot in drift, shale, sandstone or limestone and above $15 per foot in granite, per ORNL's contractors.
Installation Process
Timings below are estimates; the drilling rate is ORNL's.
Horizontal Installation
- Site survey: Mark utilities, measure available area, test soil (0.5 day)
- Trenching: Backhoe digs 4–6 ft deep trenches across your yard (1–2 days)
- Pipe laying: HDPE pipe placed in trenches — straight runs or slinky coils (0.5–1 day)
- Connection: Header pipe connects loops to house penetration (0.5 day)
- Backfill & restoration: Native soil replaced, grade restored (0.5–1 day)
Your yard will look like a construction zone for 3–5 days if the steps above run one after another. Grass typically recovers in one growing season. No heavy equipment on the loop field after installation.
Vertical Installation
- Site survey: Mark utilities, plan bore locations and access path for drill rig (0.5 day)
- Drilling: Roughly 2–5 hours of drilling per 300-ft bore at the rates ORNL's contractors reported, plus setup, grouting and rig moves — plan on 2–4 days for 3 bores
- Loop insertion: U-tube HDPE pipe inserted, bore grouted with bentonite mix (same day as drilling)
- Header trench: Shallow trench connects bores to house (0.5 day)
- Cleanup: Drill cuttings removed, bore sites restored (0.5 day)
Yard disruption is minimal. The drill rig needs roughly a 10×30 ft access path to each bore location, the bores themselves are 4.25–6 inch holes, and the only other disturbance is the header trench.
The drilling side is where vertical quotes diverge most, because geology sets both the cost per foot and how many feet you need. Our geothermal drilling and wells guide covers the methods, the regional per-foot costs, the grouting that protects your aquifer, and the permits.
Durability & Lifespan
| Component | Horizontal | Vertical |
|---|---|---|
| Pipe lifespan | Same pipe both ways; ORNL, DOE and ENERGY STAR publish no lifespan figure | Same |
| Risk of damage | Higher — shallow depth vulnerable to digging, landscaping, tree roots | Lower — deep bores are inaccessible |
| Repair difficulty | Easier — excavate to 4–6 feet | Extremely difficult — may need new bore |
| Thermal degradation | Possible in undersized fields (soil temp drops over years) | Less likely in principle, since deeper ground holds a steadier temperature — reasoning rather than a measured figure |
| Antifreeze maintenance | Same — periodic pH and concentration checks on the installer's schedule | Same |
The practical difference is damage risk: horizontal loops can be accidentally damaged by future digging (fence posts, landscaping, utility trenching). Vertical loops are far harder to disturb once installed. If a bore does fail, though, repair is harder still, and the practical answer is often a new bore.
When to Choose Horizontal
- Large, clear lot (roughly 4,500–7,500 sq ft of open yard for a 3-ton system) with no plans for future structures
- Deep, clay-rich soil without shallow bedrock
- Budget is the primary constraint — trenching ran about half the per-foot cost of drilling in ORNL's survey, and horizontal is the lower-cost column in the cost table
- Rural or agricultural property where land is abundant
- New construction where trenching is already happening for foundation/utilities
- Farm/agricultural buildings with open fields adjacent
When to Choose Vertical
- Small lot — a typical suburban ¼-acre lot, once the house and driveway are subtracted, rarely leaves the clear ground the land table calls for
- Mature landscaping you don't want to destroy
- Shallow bedrock (common in New England, Appalachian states)
- Sandy or dry soil with poor thermal conductivity
- Retrofit to existing home with established yard
- Steadier ground temperature — deep bores sit below the seasonal swing (see Performance)
- Urban/in-town lots where space is limited
Other Loop Options
Pond/Lake Loop
Coiled HDPE pipe placed at the bottom of a pond or lake — at least 8 feet deep and half an acre of surface, and $10,000–$18,000 for 3 tons, both estimates. No trenching or drilling; the water body is the heat exchanger. See our open-loop vs. closed-loop guide for details.
Open-Loop (Well Water)
Draws groundwater from a well, passes it through the heat pump, and returns it to a second well or surface discharge. Cost: $12,000–$20,000 for 3 tons (estimate). ENERGY STAR publishes a separate minimum for it — 21.1 EER / 4.1 COP for open-loop water-to-air units, against 17.1 EER / 3.6 COP for closed loop, each at its own test conditions — but it requires adequate well yield and discharge permitting, and it is not available in all locations.
Decision Guide
- Do you have roughly 4,500–7,500 sq ft (about 0.1–0.2 acre) of clear, open yard? No → Vertical, a slinky horizontal field (2,400–4,500 sq ft for 3 tons), or one of the other loop options above. Yes → Continue.
- Is bedrock within 4 feet of surface? Yes → Vertical or another loop option (trenching is impractical). No → Continue.
- Is your soil sandy/dry or clay/moist? Sandy/dry → Vertical recommended. Clay/moist → Continue.
- Are you building new or retrofitting? New construction → Horizontal (trenching is already happening). Retrofit → Either, but consider yard disruption.
- Is budget the primary constraint? Yes → Horizontal, the lower-cost column. No → Either; price both. Efficiency ratings do not break the tie (see Performance).
Land area and geology set which type a home ends up with; any national horizontal-versus-vertical percentage you see quoted is an estimate (see the FAQ).
For state-specific geology and loop type guidance, check your state geothermal guide — each one includes a regional loop type comparison table.
Your lot decides, not the technology
Horizontal and vertical loops do the same job with the same pipe. Land area and geology determine which one you can build. Drilling ran about twice the per-foot cost of trenching in ORNL's 2018 survey. That is a per-foot figure, not a per-ton one; a trench foot and a bore foot are not equal capacity. ENERGY STAR's efficiency floor is set by product and loop type, not by horizontal or vertical orientation. If your lot allows both, price both.
Frequently Asked Questions
No national percentage is available from the cited authorities. ORNL's 2018 survey put drilling vertical bores ($5.00–$15.50 per foot, 2018 dollars) at about twice the cost of digging horizontal trenches, per linear foot. As market estimates, a 3-ton horizontal loop runs $12,000–$22,000 against $18,000–$32,000 for vertical, and the two ranges overlap. ORNL, DOE and ENERGY STAR publish no operating-cost difference between the two either, so no operating-cost offset is netted against the loop price.
Only shallow-rooted plants — grass, flower beds, vegetable gardens. No trees or large shrubs whose roots could reach 4–6 feet and damage the pipe. No structures, driveways, or anything that compacts the soil. Plan your landscaping around the loop field permanently.
ORNL's 2018 contractor survey reported vertical bores of 200 to 400 feet, averaging 328 feet, with diameters of 4.25 to 6 inches. Depth depends on geology and system size; your installer sets it from a thermal conductivity test or local drilling data.
Both use the same HDPE pipe, so pipe life is not what separates them. Vertical loops are harder to damage after installation because they're deeper and out of reach of ordinary digging. Horizontal loops at 4–6 feet are occasionally damaged by landscaping or utility work. However, horizontal is much easier to repair — just excavate to the damage point.
Not by ENERGY STAR's rating. Its certification minimums are set by product configuration and loop type, not by horizontal or vertical orientation: closed-loop water-to-air units must reach 17.1 EER / 3.6 COP and open-loop units 21.1 EER / 4.1 COP, and a horizontal closed loop and a vertical closed loop fall under the same minimum. Deeper ground is steadier, which favors vertical in principle, but ORNL, DOE and ENERGY STAR publish no orientation-specific COP comparison to put a number on it.
Yes — slinky (coiled) horizontal loops pack more pipe into less trench length, which cuts the land a horizontal field needs. ORNL's contractors reported slinky loops averaging only slightly more per ton than straight horizontal runs. The tradeoffs: more pipe and fittings, and some thermal interference between coils. Slinky is a middle ground between standard horizontal and vertical.
ORNL, DOE and ENERGY STAR publish no national split between vertical and horizontal residential installations. Which one a site gets is set by land area and geology: lots without the clear ground a horizontal field needs go vertical, and rural lots and new construction have more room for horizontal.
Sources
- Liu, Polsky, Qian, Mcdonald — "Analysis of Cost Reduction Potential of Vertical Bore Ground Heat Exchanger", ORNL/TM-2018/756, Oak Ridge National Laboratory, August 2018 — bore depth and diameter, trench length, loop cost per ton, drilling cost per foot by rock type, rate of penetration, and drill rig prices. Contractor survey with eight responses; see the note at the top of this page. Verified 2026-09-03.
- U.S. Department of Energy — Geothermal Heat Pumps — ground temperature at about 30 feet. Verified 2026-09-03.
- ENERGY STAR — Geothermal Heat Pumps: Key Product Criteria — certification criteria page; minimum EER and COP by product and loop type, effective January 1, 2012. Verified 2026-09-03.
- IGSHPA — International Ground Source Heat Pump Association — the trade association's homepage, cited for context; not a design specification. Verified 2026-09-03.
Citation withdrawn 2026-09-03. This page previously cited Building Science Corporation, "BSI-070: To Those Picky About Ground Source Heat Pumps." The document could not be retrieved at the address this page used or confirmed to exist under that title, so the entry was removed rather than replaced with a guess. Nothing in this article rests on it.