An expansion tank is a small safety tank used in closed-loop hydronic heating and Water Heaters systems to protect against excessive pressure. As water is heated, it expands; without an expansion tank, this extra volume would have nowhere to go and could cause pipes to burst or the pressure relief valve to leak. The tank contains a rubber diaphragm and a cushion of air that absorbs this extra pressure, keeping the system stable. This is a critical component for the longevity of your Water-Plumbing infrastructure. You can find high-quality tanks in various sizes to match the capacity of your boiler or water heater in our store. Properly maintaining the air charge in this tank is an essential part of annual HVAC service. It acts as a mechanical "shock absorber" for your entire plumbing system. For homes with ACIq hydronic heat, the expansion tank is a vital piece of safety equipment that should never be overlooked.