What are unvented hot water cylinders?

Unvented hot water cylinders are cylinders that store hot water under mains pressure.

What does that mean?

Well, if you can imagine what a conventional heating system consists of, this old style system will typically have tanks in the loft to fill cold water to either a conventional hot water cylinder and/or cold water supplies to feed all the cold outlets, like the bathrooms and W.C.s. Sometimes, in fact most of the time, a property will have one tank that services both the hot water cylinder and the cold outlets.

Also you may have an addition of a heating system attached to the hot water cylinder. So the cylinder could be either heating up by a hot water coil from the gas boiler or an immersion heater (Electric element.) most of the time people will have a gas system heating up the cylinder but will have a switch on the wall to turn on the immersion heater if ever the boiler fails to work!

However you can just have the hot water cylinder being heated up to one of these heat sources. E.g. No central heating and gas boiler.

A switch on the wall to heat up the cylinder from the electrics.

An Unvented hot water cylinder works under the same principle as an old style cylinder but does not have tanks.

Depending on the mains pressure in your property you may need to upgrade the mains supply coming in to the building to give you the maximum hot and cold water flow rate performance.

Typically an unvented hot water cylinder will give you between 18-25 litres of hot water per minute. This hot water flow rate is much greater than any combination boiler can give and also, this flow rate can remain consistent throughout the flow even when another tap is opened.

Some unvented hot water cylinders like Megaflo have an internal air pressure charge bubble. This takes up the pressure of the hot water when it is been heated up. However some other manufacturers’, like Worcester Bosch ‘Greenskies’ unvented hot water cylinders have an external expansion vessel. This is something you need to think about when looking at how much space you have where you want to put the unvented hot water cylinder.

Also all unvented hot water cylinders have a pressure relief valve which has to terminate outside somewhere safely. This is a requirement of G3 building regulates.

The benefits of installing a unvented hot water cylinder are:

No tanks required as its filled straight from the mains!
Less storage space required as there are no tanks!
Mains pressure water so no need for pumps for showers etc!
Healthier to wash in as its straight from the mains!
Much greater flow rates of water than given by a combination boiler!

We install all the leading brands of unvented hot water cylinders like:

  • Megaflo unvented hot water cylinder
  • Worcester Bosch Greenskies unvented hot water cylinders
  • Ariston unvented hot water cylinders
  • And many more..

Please call or mail for more information on how we can install an unvented hot water cylinder for you!