The basics Method to estimate required length of borehole The methods required to estimate the length required by borehole is outlined in ASHRAE Handbook - Applications (2015). Specifically, we’ll be looking at the sizing of a vertical geothermal heat pump system. The given (known) values that we have are $q_c$ and $q_h$, the cooling and heating load of the new campus in tons, which needs to be plugged into the following Equation (1) for the required length of cooling: