What is a header tank?
In a fully open vented heating and hot water system you will often find water storage tanks in the loft. It is quite common to find two. The function of each is however quite different.
You may well find that one tank (usually the larger of the two) is a Header Tank, whereas the other (the smaller) is a Feed and Expansion Tank (also known as an F&E tank).
A Header Tank is a cold water storage vessel usually filled via a ball cock (or float valve) directly from the incoming cold water main. This tank stores the water that feeds to your hot water cylinder. The high position of the Header Tank creates 'a head' of water which determines the pressure of the hot water system in the property. System pressure can be calculated roughly by applying the following equation: Measure the vertical difference from the Header Tank to the point of outlet. A 10 metre differential will give 1 bar of pressure at the outlet. Pressure can be raised (albeit only slightly) by raising the Header Tank within the loft space.
What is an F&E tank?
A Feed & Expansion tank is typically connected to the 'heating' side (boiler or radiator circuit) of an open vented system and as its name suggests provides a method of replacing (feeding) water that can evaporate as the system gets hot whilst facilitating the associated expansion of the water contained within the system.
What should an F&E or Header Tank be made from?
Header tanks can be made from a range of materials, but metal header tanks (typically made from copper or stainless steel) are arguably better suited for use on systems where the water can become very hot - such as in solid fuel installation (wood burner, AGA, back boiler), with thermal stores or where the heat source is uncontrollable by nature.