I had the system sized by this company: http://www.energywisestructures.com/ . They seem to be highly recommended and very good at what they do. I wouldn't go down on the system size. I know it is a bit more up-front cost, but I would rather have the extra power if needed for above average summers (this was a very average year). Also, please correct me if I am wrong, but aren't the systems more efficient running in first stage vs second? So, efficiency wise, isn't it better to have a over-sized system always running in first stage than an under-sized system always running in second stage? My main goal in this thread was the loop design in the pond. It is a non-standard loop design I was trying to do myself for my particular situation/needs. The size of the system I left up to the experts. The pond loop design, however, I did myself. Other than my heating/cooling cost, how can I tell if the loop design is adequate? Thanks for all the feedback.