usually the pipes in the walls are the ones that are the most obstructed. One thing to consider with CPVC replacing a steel pipe system is that there were often ground wires connected to the steel. Telephone, main electric, bathroom, kitchen, etc. which will be broken when a non-metallic or copper system with di-electric unions is installed. I would use copper, but a do-it-yourselfer has less chance of burning the building down by using CPVC.: The pipes in my house are 50 year iron pipes. I want to replace everything except whats inside the walls to boost pressure and delivery. If I go with copper, will I have a problem with the dissimiler metals? Or should I go with cpvc to avoid this?