Types of Hot Water Cylinders

May 10, 2010 / by Barry Reynolds

Hot Water Cylinder Insulation

New cylinders should be insulated with a bonded foam jacket on to the outside of the cylinder, these are extremely efficient and will keep the water hot for a long time.

Hot water cylinders without a bonded foam jacket should be insulated with a glass fibre jacket. An 80mm thick jacket will cut heat loss by up to 75% and are very cheap at around £10.

Types of Hot Water Cylinder

There are many different shapes and sizes of cylinder to suit the space available such as an airing cupboard. The capacity of the cylinder is important which is measured in Litres. The required size for your property will depend on the number of people living in the house and water needs, your plumber will be able to advise you on the best size for your property.

There are many types of cylinder available, the 5 main types of cylinder are: -

Direct – which are only for use with Circulators because the water is heated directly.

Indirect – which are for use with any type of central heating system. This is because the water from the central heating goes through a coil of pipe within the cylinder (giving its heat up to the water in the cylinder) but doesn’t mix with the water in the cylinder. This type of cylinder usually has an air bleed on a pipe at the side, often the pump and motorised valves are located in the same cupboard

Primatic (self priming) – only for use with gravity systems because the water for the central heating is taken from within the cylinder, and is only separated by an air lock (system additives must not be used with this type of cylinder as this will come out through the hot taps)

Thermal Storage – a large type of cylinder were the main cold water is passed through a coil of pipe within the cylinder taking its heat from the thermal storage and supplying the hot taps. The central heating circuit is also taken from the cylinder.

Unvented Cylinder – This is the same as an indirect cylinder except there isn’t a header tank, and it’s connected directly to the main water supply giving mains water pressure to the hot taps and showers. This is probably the future standard because of the reliability and true mains water pressure. They come in various sizes and are ideal for the larger home.