My concern was that if I ever need to make a warranty claim, will having low CH be a legitimate reason to deny it? In reading on TFP, it sounds like the "science" behind low calcium being corrosive to metal is rather sketchy. As the theory goes, it is hoped that the calcium forms a protective barrier inside the copper pipes or the calcium decreases the water's affinity for metal. The arguments against this theory are that the calcium carbonate layer doesn't form well inside a heat exchanger (doesn't form well on the cold spots and maybe results in too much scaling on the hot spots) and that taking the calcium out of water (by softening) makes water less conductive and therefore less corrosive (I think).