If you need to replace your traditional tank type water heater, your plumber may have recommended installation of a thermal expansion tank. If you have never had one in the past, you may be wondering why or even if you need one.
First, the easy answer is many local building codes require thermal expansion tanks to be installed on storage tank type water heaters. Local building codes change over time and even if a thermal expansion tank was not required when your home was built it may be a recently added requirement. If required by local building codes, then you need a thermal expansion tank.
Even if they are not required by local building codes, a thermal expansion tank is necessary if you have a closed plumbing system. In the past, most residential plumbing systems were open systems. In an open system, water can theoretically flow both into the home and out of the home through the water supply line. If there is a drop in water pressure from the municipal supply or an increase in pressure inside the home, water could flow backwards through the water supply line.
To address concerns about contamination of the municipal water supply, many local water authorities have begun to require a backflow prevention device to be installed at each residence. Installation of a backflow prevention device creates a closed system that prevents water from flowing backwards through the water supply line. The backflow prevention device only allows water to flow into the home from the municipal water supply.
Backflow prevention devices help prevent contamination of the municipal water supply, but they create a problem for storage tank type water heaters. As water heats in the water heater, it expands. In the past this was not a problem since the excess water could flow backwards through the water supply line. However, in a closed system the excess water has nowhere to go and pressure will build inside the water heater and the home’s plumbing system.
A thermal expansion tank solves this problem by allowing the excess water to expand inside the thermal expansion tank. If you have a closed plumbing system be sure to have your plumber install a thermal expansion tank on your water heater.
