Eh, knows Jerry. I can't think of a situation off the top of my head where I'd need to transition from CPVC-FIP to CPVC-MIP, unless I ran out of couplings. heh. The literature says not to be used as a transition from CPVC to metal, so that doesn't exclude cpvc-cpvc (which isn't much of a transition :/ ), but the fitting itself only says COLD WATER ONLY.