A bunch of the geo units I service are from the '80s some vertical loop and some open loop. Some of the units have out lived the companies that made them. I just went on a call for 5-ton Jacobsen Energy Industries unit hooked up to a vertical closed loop I'm not sure how old it is I believe it's from the late '80s. We service a Comand-Air/WaterFurnace installed in '85. It's in the basement of an old stone farm house. It's rusted but keeps chugging along. What's the oldest geo unit you have in operation?