Ground Loop Sizing Calculator

In heating mode the ground only has to supply the load minus the "free" energy the compressor contributes, so ground extraction is heatingLoad × (1 − 1/COP). In cooling mode the ground has to absorb the load plus that same compressor work as rejected heat, so ground rejection is coolingLoad × (1 + 1/COP) — the plus sign instead of a minus sign is why cooling always demands more from the ground loop than an equivalent heating load.

The conductivity factor is simply 1 divided by your soil conductivity value, so it scales bore or trench length inversely — poor conductors like dry sand (around 0.5) roughly double the required footage compared to wet clay (around 1.4). Since this factor multiplies directly into the footage-per-ton figure for both vertical and horizontal loops, getting soil conductivity right matters as much as getting the load calculation right.

For heating-dominant buildings, warmer ground than the 55°F reference shortens the required loop (since there's a smaller gap to bridge), while for cooling-dominant buildings, cooler ground shortens it instead — the calculator picks the right direction based on which load is larger. The clamp keeps unusually hot or cold ground-temperature inputs from producing an implausibly short or absurdly long loop length outside that 0.7x-1.5x range.

Vertical bores use roughly 175 ft per ton because they reach deeper, more thermally stable ground, while horizontal trenches use about 500 ft per ton because they sit shallower where seasonal temperature swings and lower average conductivity mean each foot of pipe moves less heat. That's also why horizontal installations need much more total land even though each trench is typically cheaper to dig than a vertical borehole.