Why Geothermal Rules of Thumb Fail

Cool Talk with Hartzell's | Your HVAC Questions, Answered! · Jun 12, 2026 · 22m · transcript

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HOST A: Dave, you got called out to a 7 year old geothermal install in Hennessey last summer. The homeowner said the system "worked fine" in the first two years and now the back of the house is hot in July. The unit is running constantly. What did you find? HOST B: The loop was undersized by about 30 percent. The original installer used a flat rule of thumb of 600 linear feet of horizontal pipe per ton in his area. He sized a 4 ton load to 2,400 feet of pipe.

I'm Dave Hartzell at Hartzell's Heat & Air in Kingfisher, Oklahoma. 45 years in the trade, Master HVAC license. On…