The method presented by ASHRAE is a single equation that accounts for both heating and cooling modes and can be used for vertical borehole systems. This method utilises a temperature penalty that factors in the long-term borehole heating exchange effect and also includes three representative building heat loads along with their respective thermal resistances.

IGSHPA present calculation methods for the length of pipe required for vertically bored, horizontally bored and horizontally trenched GHE systems, along with variations of each method for heating and cooling. For bored systems, it is assumed that the ground, from which heat is exchanged, has a constant temperature all the time. This assumption works well when the amount of energy gained from and released to the ground is equivalent. However, if this assumption becomes false at a point in time, an unbalanced ground load correction factor needs to be verified to adjust the borehole length.