While this is mainly for the pros, I thought it would also help some homeowners so I am posting it here. A client called today asking about water around his Geo. I stopped out to check it out and found ice on exposed loop line surfaces, along with water dripping from the humidifier because of a clogged drain. I fixed the "water around his Geo" problem but was curious about the ice so I ran a Heat of Extraction... GeoComfort E036 (With a scroll compressor kit retrofit) Three 150' vertical closed loop system. Pressure in 43 PSI out 36 PSI Delta P=7 PSI EWT 33.2* LWT 27.5* Delta T=5.7* 7 PSI @ 30* EWT = 11GPM 11 GPM X 5.7* X 485(brine)=30,409 Btu/Hr Heat of Extraction rated at 18,400 Btu/Hr @ 30* EWT As you can see we were pulling TOO much heat from the ground. I backed the flow off to 9 GPM and ran the numbers again... Pressure in 41 PSI out 36 PSI Delta P=5 PSI EWT 32.5* LWT 27.7* Delta T=4.8* 5 PSI @ 30* EWT = 9 GPM 9 GPM X 4.8* X 485 (brine)=20,952 Btu/Hr...much closer to published ratings. An hour after the adjustments the loop field temperature has come up two degrees. By having just 2 GPM more flow, we were over drawing the loop field design and were driving down the temps.