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In an unvented hot water cylinder system there is no cold water storage tank, they are mostly in the loft or the highest place in your home – instead a sealed hot water cylinder is fed directly by the cold water mains. An unvented cylinder is kept under pressure from incoming water supply and is heated by either immersion heaters (a direct model) or by a heat source located outside the vessel such as a boiler or wet solar system (an indirect model).

An unvented cylinder will have outlet pipe work connected to it that distributes the heated content of the cylinder (hot water) to multiple outlets around the house. As soon as an outlet (i.e tap, shower) is used, the pressure of the incoming cold water displaces the hot water content in the cylinder towards the open outlet at mains pressure.

Unvented hot water cylinder  systems are ‘sealed’, so they require an expansion vessel either next to or incorporated within the boiler or cylinder. An expansion vessel allows for the expansion of water in the system as it heats up, and accommodates the increase in pressure by up to 3.5 bar.

Unvented hot water cylinders are designed to withstand considerable internal forces and are extremely safe to use when fitted with all the correct pressure equipment. They are usually made from stainless steel due to the high tensile strength that can be achieved from a fairly thin sheet.


Unvented hot water cylinders free up lots, valuable space in your property and  provide stronger water pressure than an open gravity vented system. This is because unvented cylinders are directly supplied by the mains, but of course this depends on the strength of the mains in the first place.

Unvented hot water cylinders are also perfect space-saving options for the modern home. An unvented hot water cylinder doesn’t require a feeder tank in the loft and frees up valuable space in your property. Unlike vented cylinders, the unvented cylinder doesn’t rely on gravity to function, so it can be installed almost anywhere in your home! This makes it easier to store in a place more suitable for you.

Other advantages of installing an unvented system include reduced noise in the system. This is due to the fact that there is no cold water filling up the water storage cistern. The unvented system is completely sealed too, so the water is not at risk of contamination and you don’t have to worry about the water tank freezing throughout winter.

Is a new cylinder needed ?

An unvented hot water cylinder lasts for 30 plus years, give and take a few years. If your cylinder is beginning to leak water, losingg hot water pressure  then it is time to replace it. At any time, the leaking water can get worse and cause expensive damage to your property. Always check for any damp patches surrounding the cylinder and check for any signs of water damage.

Unvented hotwater cylinder: About
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