Geothermal Loop Length

Estimated loop length from design BTU and BTU-per-foot benchmarks (simplified).

Run the calculator

Example

You enter

Heating design (BTU/hr) 60000
Cooling design (BTU/hr) 48000
Soil class clay
Loop type vertical

You get

BTU per linear foot 40 BTU/ft
Design (Btu) 60000
Estimated loop length 1500 ft

Checked against published worked examples from: IGSHPA / ASHRAE Handbook (Applications).

Details, formula, and sources

Formula or tableRequired loop length = peak design BTU/hr (max of heating, cooling) / BTU-per-foot benchmark from soil-class lookup (vertical sand 30 / clay 40 / rock 55 BTU/ft; horizontal sand 18 / clay 25; rock not supported horizontally).

Source and editionDOE / IGSHPA technical reports by name (U.S. government, public domain).

Free accessDOE reports free at energy.gov / nrel.gov. IGSHPA training materials licensed.

What governsEstimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.

API field namesheating_btu, cooling_btu, soil, loop_type, btu_per_ft, design_btu, length_ft

BTU-per-foot table data/hvac/geothermal-soil.json keyed to soil class and loop typeDOE technical reports