Unvented hot water is the premier method of heating and storing hot water.  Reputedly devised by an Englishman as far back as 1861, unvented systems are commonplace throughout Europe, South Africa, North America and Australia, although the UK remains one of the last bastions of the traditional low pressure vented system. However, times are changing. The demands from discerning householders for increased performance, sophisticated taps and showers, and aesthetic styling have produced a growing trend towards the installation of unvented systems in the UK, which will continue to increase in popularity.

How the unvented system works


The basic difference between the high pressure unvented systems and a traditional low pressure vented system is that we no longer require the cold water storage cistern.  Instead, the unvented unit is fed direct from the mains cold water supply.  Hot water drawn from the unit is then replenished from the mains supply.  As water expands when heated and (as the name implies) there is no vent pipe, the expanded water within the system is accommodated by either an external expansion vessel or, in the case of bubble-top units, an internal air bubble within the unit which is generated when the system is commissioned.  To maximise the benefits of the unvented system, a sealed heating system, if applicable, can also be installed providing the boiler used is compatible.  The significant benefits to be gained from the installation of an unvented hot water storage system are outlined below.


  • Superior performance – ensures constant high flow rates at all outlets and allows rapid filling of baths
  • This is the system will give you the best showers possible
  • Balanced pressures – far wider choice of taps and showers can be used
  • Reduces hydraulic noise in system – no filling of cold water storage cistern
  • Eliminates risk of freezing and burst pipes in roof space
  • Eliminates risk of contamination – no cold water storage cistern in roof space
  • Frees roof space – can be utilised for loft conversions
  • Energy efficient – reduces fuel costs
  • Aesthetic looks
  • Superior performance and flow rates, ideal for multi-bathroom dwellings

Unvented hot water is not suitable for every property.  Please arrange a free survey to see if your property is suitable.  As a minimum you need to have good pressure and flow rate from your cold water main.  As a basic guide to see if your property may be suitable.  Your mains cold water tap should be able to fill a standard black bucket in under 25 seconds.

Unvented Hot Water Storage Systems are subject to the legal requirements of Building Regulation G3 and can only be installed by a “competent person” in strict accordance with the relevant manufacturer’s Instruction Manual, Building Regulation G3 and the current Water Byelaws. It must be installed, commissioned & maintained by a qualified engineer (gas safe registered does not automatically mean unvented qualified)