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vented vs unvented

How to choose between vented or unvented cylinders

There are some important factors you should consider when you make a choice between VENTED and UNVENTED cylinders.

  • The size of your house – the number of bathrooms
  • The type of heating system
  • The pressure level from the mains supply
  • The cost of installation and routine maintenance

What is a Vented Hot Water Cylinder?

A vented hot water cylinder is the more traditional approach where there is a cold-water storage tank, which is kept in the loft, the natural pull of gravity carries this water via a vent pipe down to the hot water cylinder which heats the water.

Vented cylinders rely on gravity and the height of the cold-water tank dictates the pressure. The greater the height, the more powerful the water pressure. This means that the cold-water tank will be usually placed in the loft.



Benefits of vented hot water systems

  • Vented hot water systems are much less complicated to install; therefore, they are more affordable and easier to maintain.
  • If the mains water supply is cut off, you will still have access to the tank of water in the loft.

Disadvantages of vented hot water systems

  • The biggest challenge is vented cylinders may deliver a lower pressure of water
  • The system takes up more space in the home with the combination of the cold-water tank and the hot water cylinder.
  • Vented cylinder installations rarely deliver hot water at the pressure of an unvented system. You may need an additional pump to boost water flow.

What is an Unvented Hot Water Cylinder?

Unvented hot water systems don’t require a water storage tank. Instead, a sealed hot water cylinder is fed directly by the cold-water mains, and therefore can deliver hot water at mains pressure.

The water can either be heated directly via an immersion heater or indirectly via the central heating system, solar thermal technology or other renewable energy such as heat pumps and biomass.

Unvented hot water cylinders are ‘sealed’, so they require expansion vessels to be fitted to allow the expansion of water in the system as it heats up. Unvented cylinders are designed to withstand considerable internal forces and are extremely safe to use when fitted with all the correct pressure equipment.

Outlet pipework connected to the cylinder distributes the hot water to multiple outlets around the house. As soon as an outlet (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.



Benefits of unvented hot water systems

  • Unvented cylinders don't require a water tank which is ideal if you are pushed for space as well as offering more flexibility when siting the cylinder.
  • Unvented cylinders don't rely on the pressure from the mains. This means that the unvented hot water cylinder system can be installed almost anywhere you like, without having to depend on gravity for good water flow.
  • It is a completely sealed system, there is no need for a tank of water that could freeze in winter or be at risk of contamination.
  • Unvented cylinders operate at mains pressure to offer much better water flow rates.

Disadvantages of unvented hot water systems

  • Unvented hot water systems are more complex than vented cylinders, so are more expensive to install and maintain.
  • Unvented cylinders aren’t always compatible with modern power showers and mixers.
  • Because unvented cylinders are linked directly to the mains, these will not provide hot water if mains are turned off.


Unvented stainless-steel hot water cylinders are considered a much better choice for new installations and for the replacement of existing ones. However, It is important to choose the right cylinder type to avoid any compatibility issues. If an unvented water cylinder is installed on a regular heating system, it may cause an increased pressure far above what the old network pipes and radiators can handle.

On the other hand, if the pressure from the mains is relatively low, installing an unvented system will not lead to any complications and you can enjoy an improved shower and bath performance all year round.

If you would like to upgrade your hot water cylinder check out our shop where we carry well-known brands like Telford, RM Cylinders and Megaflo.


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