New Jersey follows the International Plumbing Code (IPC) in which the requirement for an expansion tank for a water heater depends on the specific circumstances and local regulations. Expansion tanks are commonly recommended when a closed water system is present, helping manage thermal expansion. To ensure compliance, it's advisable to check with the local building department or consult with a licensed plumber in New Jersey. Building codes and regulations can be updated, so it's essential to verify with current local authorities for the most accurate information.