Short answer? If your home has a “closed” plumbing system, then yes, you’ll need an expansion tank. You see, homes have either an open or a closed plumbing system. A closed plumbing system prevents water from flowing in the reverse direction (i.e., water won’t flow back into city lines once it enters your home’s pipes). Since most new homes are built with a closed plumbing system, chances are, you’ll need an expansion tank. We’ll explain why below.