Estimate the heating and cooling requirements for your building and the amount of hot water required. You can base this estimation on your building's current energy needs factoring in square footage, insulation and natural heat loss (from windows and doorways). This information will help you determine the amount of energy required from a geothermal heat exchanger. Computer software is available to assist you in entering all the variables necessary for an accurate estimation.
Determine the nuances of the property the system will serve. Take into consideration such factors as property size, bedrock and nearby water (ponds or lakes). The size of the property can greatly influence the sizing of the system. For example the more compact vertical system may be more viable on small lots, where an expanded horizontal system (possibly extending to any pond that may be on the property) may be better for larger properties.
Use the estimated energy requirements and the property characteristics to determine which size geothermal system is most practical for your building. Performing your own calculations can give you an estimate of the size system that you need. However, the final calculations for determining the proper size of a geothermal system will be performed by the geothermal specialists contracted to do the work on your home.