Unvented Hot Water Systems

Unvented Hot Water Systems

An unvented hot water system is much more energy efficient than the traditional open vented systems because they are not open to the air in any way.  This means that they heat the water stored in them quicker than vented cylinders.  Vented systems usually have a hot and cold water tank installed in the loft. Cold water is stored in one cylinder and fed to the hot water tank; which has an open vent pipe to release steam into the atmosphere. Megaflo logo This kind of system has several drawbacks: it can be noisy and because of its location in the loft, pipes and tanks are liable to freezing. There is also a risk of water contamination as well as unreliable water pressures and temperature fluctuations.  An unvented hot water system resolves many of these issues as it doesn’t have a cold water tank and the sealed (unvented) hot water cylinder is instead fed directly from the cold water mains.


There are two types of unvented system:

Indirectly heated unvented systems – are connected to a traditional heat source such as a boiler or perhaps solar panels. This is the most common type of unvented system and is fairly easy to install when converting old central heating systems.

Directly heated unvented systems – these are fuelled by electric, gas or oil directly and are used often in brand new properties. Before you consider installing an unvented system you must make sure that you have a mains water supply which is capable of producing a minimum flow rate of 1.5 bar and 20 litres per minute flow rate.


There are many advantages to having an unvented central heating system installed:

  • Supply high water pressure for more powerful showers so booster pumps are not required
  • Quicker and more energy efficient at heating water; this will save you time as well as money
  • Balanced pressure between hot and cold taps and also stable pressure for showers meaning that temperature can be controlled better
  • Easy to install and can be placed anywhere
  • Space saving because you don’t need a cold water tank in the loft, which is particularly good if you want to convert your loft
  • Reliable and low maintenance
  • More hygienic – in comparison to water stored in a tank, which is at risk of contamination
  • Less risk of frozen pipes
  • Quicker installation time compared to the fitting of a vented system


Prices will vary depending on the size and make that you choose, and whether they’re direct or indirect models.


Designtech Heating are fully qualified ‘Megaflo’ installers.  Megaflo are renowned, top quality unvented hot water cylinders and are manufactured by a company called Heatrae Sadia.  Heatrae Sadia are the UK’s leading manufacturer of hot water systems, and Megaflow is their flagship brand. We also install, maintain and service several other cylinder makes such as the Vaillant uniSTOR.


Please contact us for more information and a no-obligation quote.

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