I am a homeowner, not an expert. In 1985 when my south-central Pennsylvania house was newly-built, a 4.5 ton CanTherm unit was installed and connected to a 1,500-foot closed loop buried 3-feet in limestone soil, which I suppose was cutting edge at the time. In 2005, a 4.5 ton FloridaHeatPump replacement unit was connected to the same loop. The house is efficient for natural cooling from breezes, so the heat pump isn't turned on unless it's hitting 83F outside. keep the thermostat set at 78F. This year, there are more days hitting 90F and up, and the heat pump was blowing air only slightly cooler than room temperature. Fluid was coming in from the loop at 80-85F. After these 33 years, I've never had a problem with either of the two heat pumps keeping pace with cooling. The installer of both units is well-experienced in residential, commercial and government geothermal installations across the mid-Atlantic states. After two visits in July and August, the FloridaHeatPump checked out okay and the conclusion is my loop is too shallow at 3-feet, and will have to be abandoned and replaced with a new loop. I was informed that horizontal closed loops are now placed 5-6 feet underground, or I could opt for a vertical closed loop with approximately 4.5 x 150 feet of well depth. I'm finding it hard to accept that a loop with 33 years of proper function at its 3-foot depth is now failing with these 90-degree days. Is it possible that the glycol solution in the loop could be at fault, like automotive anti-freeze that needs to be replaced? Has global warming pushed its impact down past the 3-foot depth?