**Why is the expansion tank always found above the hydronic heating system? **
An added benefit or function of an expansion tank (in addition to providing a place for expanding heated water) is that the boiling point of the water in the hydronic heating system can be raised by elevating the tank.
When you elevate or raise an expansion tank you increase the head, which is a term used to describe the difference in elevation between two points in a body of fluid. When you increase the head, you increase the pressure.
This results in the ability to heat water at a significantly higher temperature without generating steam. The more heat that is supplied to the heat-emitting units, the better.
That is why you will always see an expansion tank over the boiler.
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