Thermal expansion tanks are a relatively new addition to most home water supply systems that prevent pressure from building up in the plumbing system. When a storage type water heater is installed in a home, there needs to be some provision to allow for the water to expand as it heats. In older systems this was not a problem since the water could flow backwards through the water service line.
Until recently, most home water supply systems were “open” systems that allowed water to flow in either direction from the municipal water main. In these older systems, there was nothing to prevent water from flowing backwards through the water service line which had the benefit of accommodating water expansion in the home’s water heating system.
However, more and more municipalities are installing check valves or backflow prevention devices at the water meter to prevent water from flowing backwards into the water main and potentially contaminating the water supply. In these “closed” systems, water has nowhere to go as it heats and expands. In a home plumbed with copper pipes, the water pressure can rise above 150 psi due to the expansion of the water as it heats up inside the water heater.
A homeowner may notice water escaping from the pressure relief valve at the water heater when this happens. Too much pressure in in a home’s water lines can cause leaks, broken pipes, or a ruptured water heater. To prevent these problems, have your plumber install a thermal expansion tank. These tanks cost less than $100 and use no energy. They allow your home plumbing system to maintain a constant, safe pressure. In many areas, a thermal expansion tank is now required by local building codes.
