Expansion tanks – are they really necessary?

Today we explore a common question from homeowners who might have received some incomplete information. “Are expansion tanks really necessary?”  The correct answer is: it depends. First let’s talk about why we use an expansion tank.

A thermal expansion tank is designed to maintain safe water pressure in a homes where a backflow preventer is in use. Backflow preventers are installed in newer homes or homes that have well water and they create what’s called a closed loop system.  When your hot water heater comes on the water expands and in a closed loop system it has nowhere to expand to which causes high operating pressures. In a good scenario it may cause the water heater safety relief valve to open.  In a bad scenario you could be looking at flooding due to broken plumbing components.  Installing an expansion tank on the cold water side of the water heater creates a cushion for unintended pressure spikes.  

If a home does not have some form of backflow preventer this pressure is put back into the municipal system.  

The bottom line is if your home has well water or a back flow preventer you need an expansion tank for safety (according to current Ohio Plumbing Code).  If you’re on city water and have no backflow preventer your home does not need an expansion tank. In the second case it does not hurt to put one in but it is not absolutely necessary.

Expansion tank mystery solved.