Water heater expansion tank. Ideal to maintain the efficiency and safety of your home's water system. This thermal expansion tank is designed to manage pressure build-up in closed, potable water systems. By preventing unnecessary pressure increases, this tank ensures your water heater's pressure relief valve stays closed, which not only saves energy but also eliminates potential safety hazards. With a Water Worker expansion tank, you can enjoy peace of mind knowing that your system is running smoothly, efficiently, and safely.