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  • Converting To Unvented Hot Water

    Converting over to unvented hot water has many advantages over vented hot water, it is also more cost-effective to use.

    First and foremost before you even think about converting to unvented hot water,

    the incoming water mains need to be checked to ensure you have adequate pressure and flow rate.

    Unvented hot water cylinders require at least a minimum of 1.5 bar water pressure for them to work correctly,

    they will work on the lower pressure, but you will only be able to use one hot outlet at a time.

    So what’s involved in converting to unvented hot water.

    If your hot water tank is vented, this means you will have a cold water storage tank somewhere,

    normally it’s located in the loft, but it could be in a cupboard.

    The cold water storage tank can be removed, as it will no longer be needed,

    this frees up valuable space for you to use.

    Your vented hot water cylinder can be drained down, and replaced with a new unvented hot water cylinder.

    The pipework will need altering to connect to the new cylinder, but it’s normally a straightforward job.

    When unvented cylinders heat the water, the water expands,

    so it needs some form of expansion vessel fitted to the pipework.

    Some manufacturers produce unvented cylinders with built-in expansion vessels,

    though they can be a little on the expensive side, they save on space.

    Other makes of unvented hot water cylinders come with an expansion vessel supplied in the box, that’s needs fitting externally.

    The size of the expansion vessel is determined by the size of the cylinder.

    When converting over to unvented, you will need a new safety discharge pipe installed.

    It’s connected to the cylinder and needs to be able to discharge in a safe place,

    normally this would be into a drain, or at low level on the outside of the property.

    Heating of the water is the same as the vented cylinder, either by your boiler or by immersion heaters.

    What are the benefits of unvented hot water?

    Powerful mains pressure in the shower, now you will be able to take a real shower without the need for a pump.

    If you already have a pumpfitted to your hot and cold water system, this can be removed, no pump, no noise.

    Hot and cold supplies will be balanced,

    meaning both will have the same pressure at the outlet.

    Filling a bath will take less time to fill, compared to a vented cylinder.

    No need to have any cold water storage tanks,

    meaning more hygienic compared to vented, bacteria can grow in stored water tanks.

    No more vermin entering the cold water tank in the loft and contaminating the water.

    Faster reheating of the hot water and more economical to use,

    the new unvented cylinder hold the heat for longer, compared to vented.

    Unvented hot water systems are now installed in all new build properties.


    Just like your central heating boiler, the unvented hot water cylinder requires an annual service carried out.

    This must be carried out by a company who is registeredto work on unvented systems.

    It’s a good idea to find a company who is registered for both and can service the unvented cylinder and boiler at the same time.