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There are 5 main types of hot water cylinder available. Each with different operating methods and for different purposes. Listed below are the different types of hot water cylinders available detailing the way they work and for which purpose each is used for.

Unvented

Unvented Cylinders work off the mains pressure water, and therefore use the water mains pressurised system to move the domestic hot water around the property, and so eliminates the need for a header tank in the loft.

Unvented Cylinders offer higher hot water flow rates, and are therefore able to provide higher water pressure for showers, baths etc.  As an Unvented Cylinder does not require a feeder tank, this frees up valuable space in the loft area, and also gives you the option to site the Cylinder anywhere you want thus freeing up further space in your airing cupboard.

Unvented Cylinders are generally manufactured out of top quality stainless steel, this ensures long life and durability, and Unvented Cylinders can also carry a manufacturer’s guarantee of up to 25 years. E.g. the Gledhill cylinders range.  Other Manufacturer’s guarantees may vary.

Vented Cylinders

A Vented Cylinder (or cistern fed) has a header tank that is usually situated within the loft area.  This header tank feeds through the cold water from the mains feed, and relies on gravity to pass the water through the pipes to your heating/hot water system.  A vented hot water cylinder is normally associated with a conventional heating system.

Vented Cylinders are manufactured out of copper, with the copper varying in thickness measured in grades.  The better the grade, the better the resistance to copper corrosion, and therefore advances the longevity of the cylinder.  A domestic vented copper cylinder is usually Grade 3 such as Gledhill hot water cylinders.

Direct

A Direct Cylinder is heated via an internal element, usually an immersion heater.  The water in the cylinder is heated by these immersion heaters directly, hence why the cylinder is called “direct”.  The water in the cylinder is not heated via any other heat source.  Once the water has been heated, it is then fed out the top of the cylinder and supplied to the required outlet.  E.g. Bath or Tap.  Larger capacity Direct Cylinders can have up to three internal immersion heaters, to ensure the maximum amount of hot water is available.  Direct Cylinders are available in Vented or Unvented Models.

Indirect

Indirect Cylinders are heated via an external heat source, such as a boiler or solar panel.  The water inside the cylinder is then heated using an internal coil/heat exchanger, which transfers the heat obtained via the external heat source, to the water inside the cylinder.  Although the cylinder is heated via an internal heat exchanger, the original heat is obtained externally, and therefore why it is commonly referred to as “indirect”.  Indirect cylinders may be fitted with immersion heaters, acting as a supplementary heat source, but they will still be considered to be Indirect Cylinders. Some manufacturers supply an immersion heater as standard, therefore any additional ones will need to be purchased separately.  Indirect Cylinders have a faster heat up and recovery time than that of a Direct model. Indirect Cylinders are available in Vented or Unvented Models.

Solar Cylinders

Solar Cylinders are specially designed for Solar Heating installations.  A mixture of water and a special Glycol liquid (specially designed to absorb maximum heat from the sun’s rays) is circulated through pipe work in the solar panels.  This liquid is then returned to the cylinder where the heat is transferred to the stored water via an internal coil/heat exchanger, the liquid is then pumped back to the solar panels to be reheated.

An additional coil is also required to obtain heat from an alternative source, if the heat from the Solar Energy is insufficient.  This is most commonly referred to as Indirect “Twin Coil” Cylinder.  Direct Cylinders can be used for Solar Power, with the added heat source being supplied via the internal immersion heaters.  It is advised however, to install an Indirect Cylinder, as this provides faster heat up and recovery time.

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