This machine has a full 8" membrane in stainless steel post with a circulating pump. It is the only over the tank model that will go from 2 to 8% in one pass. This unit is engineered to drain completely and does not need to be protected from freezing. Electrical needs are a 220v 20 amp circuit with a GFI. 3 years old, and includes a membrane storage vessel.$5200.00. $8000 for a new one. 315-486-9801