With an indirect water heating system and cylinder,
the water that circulates around the boiler, pipes and radiators
is kept totally separate from the stored water in the cylinder
that is used for bathing.
Heating system components are generally made of a mixture
of metals including iron and steel. Oxygen and water are very
corrosive and heating systems need to be protected with chemicals
to reduce the threat of corrosion. The water for bathing is
kept separate from the heating system water by use of an indirect
heating coil or heat exchanger.
From the outside the indirect cylinder looks identical
to the direct cylinder save from two additional pipe connections
on the side of the cylinder. Inside the cylinder a coil heat
exchanger is installed, which allows hot water from the boiler
to flow into the upper connection and leave at the lower connection
to return to the boiler for re-heating. The hot water in the
coil indirectly heats the water in the cylinder.
This is the traditional open vented hot water
and heating system used in many family households in the UK
and is suitable for coal oil and gas fired heating systems.
This system is often supplemented with an immersion heater element,
as a back up, which heats the water directly should the boiler
break down.
