Thermal conductivity is the physical property of a material that determines how easily heat can pass through it. In order to properly size a ground loop heat exchanger for a geothermal heat pump system, knowing the thermal properties of the earth where the heat exchanger is installed is critical. This information can be obtained from a formation thermal conductivity (FTC) test and input directly into most of the popular design software programs.


The thermal conductivity of the formation determines how easily heat can be conducted to and from bores in a geothermal loopfield. For example, in a formation with high thermal conductivity, the loop temperature required to reject a given amount of heat to the ground would be less than the loop temperature for a formation with a lower thermal conductivity. Higher loop temperatures for cooling result in reduced heat pump performance and higher operating costs.

Why Consider FTC Testing?

  • Proper testing enables ground loops to be sized to match the existing formation conditions.
  • Precision designs save money on drilling, grouting and pipe costs.
  • Proper design allows the system to run more efficiently.
  • The obtained information provides for a better estimate of installation cost.


  • Unmatched Experience
    • Over 14 years of experience in measuring and calculating thermal conductivity of various formations.
    • Over 200,000 hours of accumulated data has been analyzed from more than 4,500 separate tests.
  • Data analysis performed by Mechanical Engineers with research backgrounds.
  • Long test times provide a reliable value for average formation thermal conductivity.
  • Dedicated to quality testing and data analysis.
  • Follows ASHRAE recommended procedures as found in the ASHRAE HVAC Applications Handbook and the IGSHPA Design and Installation Standards.
  • GRTI offers a variety of approaches to obtain an analysis (see various FTC options).