What is unvented hot water?

Unvented hot water cylinders are often known as a "Megaflo". This is in the same way that vacuum cleaners are often called "Hoovers". "Megaflo" is a brand name of Heatrae Sadia. Click here for details.



At the centre of an unvented hot water systems is a high efficiency pressurised cylinder.


When a system is installed, both the hot and the cold water supplies within the dwelling, deliver water at all taps and shower outlets at mains water pressure.


Cold water from the mains is delivered to the base of the cylinder, the water is heated, then when a tap or shower is turned on the mains water pressure pushes the hot water out.


They are very efficient at delivering a large volume of high pressure hot water to all taps and showers throughout the property.


Unvented hot water systems exceed  'Best Practice' for recovery times and insulation levels. This means that the system heats up quicker and is more efficient at retaining the water temperature.


There are other benefits too, an unvented hot water system does not require water tanks in the loft, so the existing tanks can be disposed of. This makes an unvented hot water system more hygienic and space saving.


The location that unvented hot water cylinders can be installed is very flexible, It does not need to be located in the airing cupboard. The system cylinder could be installed somewhere less central, such as the garage.

Some of the advantages of unvented hot water over traditional hot water cylinders.

  • Balanced pressures at hot and cold taps.
  • Potable (drinking) water at all taps.
  • High pressure and hence high flow rates of hot water.
  • No need for noisey shower/booster pumps.
  • Fast filling baths.
  • High performance showering throughout the house.
  • Quicker to install.
  • Quiet running.
  • Retains water temps. longer than traditional cylinders.
  • Fast recovery (typical 15-20 mins for 125L).
  • No cold water storage cistern in the roofspace
  • No fear of frozen loft pipes

We are qualified installers.

It is the law that only suitably qualified engineers work on unvented hot water installations, those being in possession of a G3 certificate. We are qualified, and once we have completed the installation of your cylinder we will notify the Gas Safe Register, who in turn will issue you a building regulations compliance certificate. This certificate is a requirement for any future Home Information Pack.