Indirect System ~ this is a more complex system than the direct
system but it does overcome the problem of furring which can
occur in direct hot water systems. This method is therefore
suitable for hard water areas and in all systems where a central
heating circuit is to be part of the hot water installation. Basically
the pipe layouts of the two systems are similar but in the indirect
system a separate small capacity feed cistern is required to charge
and top up the primary circuit. In this system the hot water
storage tank or cylinder is in fact a heat exchanger † see page 776.Hot Water Installations