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Solar water heating system expansion tanks

In a closed loop system, it is vital to fit an expansion tank. This is because the fluid that runs along the pipes taking the heat from the collectors to the hot water storage tank is usually composed of water with antifreeze added.

When the fluid is added to the system, the operating pressure is set and it will occupy a given volume based on temperature.

When the temperature rises, the fluid will expand and increase in volume.

This is where the expansion tank is used.

It consists of a chamber inside which is a bladder or diaphragm filled with air which is locked inside. The expansion tank allows the fluid to expand safely by compressing the air inside the bladder.

The size of expansion tank required depends upon the amount of fluid inside the system and the length and diameter of the pipes in the system.

As a rough guide, if the system has up to 6 gallons of fluid in the loop, a 2 gallon expansion tank is normally adequate.

With a suitable tank in place, temperatures can go from zero to 200 degrees with the fluid in the loop remaining at the same pressure.