What is an expansion tank?

An expansion tank is used in closed loop solar heating systems as the high temperatures cause a change in the liquid’s volume. To accommodate this change in volume, an expansion tank is needed. To calculate the size of tank you need to know how much fluid is in the system. Your tank should be 5% of the total liquid volume in your solar heat loop if you are using water. If you use a glycol (50%/50%) mixture then you should allow for 10% expansion.