I have a Waterfurnace Envision NDV049 (4-ton) system on two (2) 350' vertical wells. System never goes beyond Stage 1 cooling, which has a heat of extraction of about 20,000 btuh. Delta T across the exchanger is steady at 3.3F, so flow back-calculates to 12 gpm, which is reasonable. So the system works great is sized correctly for the load, etc. My concern is with the health of the loop. The loop temp was entering at 45F on 12/17 (5 weeks ago), but the season has been long and the system has been running quite a lot. Loop temp was 40F last week and 37F today - with 6 weeks or so more of cold weather on the season. My feeling is that if the EWT must go below 30F, then the ground loop is not transferring heat to the loop fast enough. The system will continue to function down to 20F with sufficient flow (>11gpm), but the "normal" operating range is published as 30-70 for heating. Please give me your thoughts.