unvented hot water

When an un-vented hot water system is installed both the hot and the cold water supplies within the dwelling, deliver water at the taps or shower outlet 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.

An un-vented hot water storage cylinder can be heated directly via an immersion heater or indirectly by most heating systems providing it is not a solid fuel burning appliance They are ideal where high performance is required or in multi story properties where it would be difficult to gain the necessary head of water via a cold water storage tank to feed taps on the upper floors


Unvented Stored Hot Water

This system is particularly advantageous where there is a high demand for hot water such as properties with more than one bathroom or where improved shower performance is required without the use of a pump. Also advantageous where no head is available for cold water storage tanks i.e. loft conversions or flats.

Some older systems can be upgraded using the existing boiler subject to building regulations. However, it is generally advantageous to use a purpose-designed pressurised system boiler which includes, within its case, all the components required for primary pressurisation.

Systems are available giving pressurised stored hot water and conventional central heating (no cold water storage tank but retaining central heating header tank) or pressurised central heating and conventional stored hot water (retains cold water storage tank but no central heating header tank) or combinations thereof.

combi-boilerUnvented Cylinders


  • Balanced pressures at hot and cold taps.
  • High performance showering throughout
    the house.
  • High pressure and hence flow rate of
    hot water.
  • Fast filling baths.
  • Potable (drinking) water at all taps.
  • No cold water storage therefore no contamination.
  • Quicker to install Quiet running Fast
    recovery (typical 15-20 mins for 125L)
  • No fear of frozen loft pipes


  • No storage back up if mains water fails.
  • Poor mains water pressure will cause
    poor performance.
  • Water must be pre-heated