I've been trying to educate myself on loop sizing and learn from mistakes others have made before I dive into the geothermal owners group. I try to "think out of the box" whenever possible and absolutely subscribe to KISS principles ...unless it's my hobby ;-) There are lots of questions from owners that have undersized loops or problematic systems. 1) Is there any reason you could not install a standard water heater in the loop circuit? BTU are BTU regardless of the source and at low temperatures (say 35 degree water temp) a std water heater is going to be close to 100% efficient. Yes it would simply be an auxiliary heat source instead of the electric back-up coils but would be much cheaper to operate although more expensive initially. 2) most designs I have seen have no reservoir tank (or a very small one) for the loop water. I would think it would make sense to have a "flywheel" to help absorb spikes and act as an expansion tank to keep air out of the loop (if plumbed in properly) 3) I understand how turbulent flow greatly improves heat transfer in a heat exchanger but I find it hard to believe that a length of low conductivity plastic pipe running though even lower thermal conductive soil will benefit from high flow rates since it will take significantly more energy to produce the flow. I'll step back and prepare for the "silly newbie" answers I'm sure are out there.