Slinky Loop Trench Calculator
Determine horizontal geothermal slinky loop trench footage, coil pitch overlap, total HDPE pipe requirements, and excavation backfill cubic yardage.
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Horizontal Slinky Ground Loop Mechanics & Geometry
Where sufficient land area is available, horizontal slinky ground heat exchangers avoid the high drilling costs of deep vertical boreholes. Slinky loops consist of overlapped circular coils of 3/4" HDPE pipe rolled out flat along the bottom of wide trenches excavated 5 to 7 feet below grade, beneath the regional winter frost line.
Slinky Loop Geometry & Sizing Rules
- Pipe-to-Trench Multiplier:
A typical 3-foot diameter coil with an 18-inch pitch packs approximately 5.0 to 5.5 feet of HDPE pipe per linear foot of trench. - Trench Length Guidelines:
Moist soils typically require 120 to 140 linear feet of trench per ton (approx. 700 to 800 ft of pipe/ton). Dry soils require 160 to 200 feet of trench per ton. - Trench Spacing:
Parallel horizontal trenches must be separated by at least 10 to 12 feet to prevent overlapping soil thermal depletion zones over long operating seasons.
Frequently Asked Questions
How much land area is needed for a horizontal slinky ground loop?
A typical 4-ton residential system requires approximately 500 to 600 linear feet of trench. With 10 to 12 feet of separation between trenches, an open yard area of 1/4 to 1/2 acre is typically required.
What depth should horizontal geothermal trenches be dug?
Horizontal trenches must be excavated 5 to 7 feet deep to ensure the loops remain well below the maximum winter frost penetration line and avoid summer solar surface overheating.
What is the slinky coil pitch?
The pitch is the center-to-center spacing between overlapping circular loops (typically 12, 18, or 24 inches). Tighter pitch packs more pipe into less trench length.