Vented or Unvented Hot Water System?

The majority of homes in the UK rely on the function of a hot water storage cylinder/system to supply hot water. But knowing which type of system is best for your needs (depending on space and budget) can be confusing if you are unfamiliar with the choices.

Vented Hot Water System

basin tap

This produces direct water heating and is common especially in older properties. Cold water is supplied to the system typically from a head tank in the loft. This is directed into the bottom of the storage cylinder and heated up. The hot water rises to the top of the cylinder where it can be utilised by the taps. As the hot water is used it is replaced by cold water from the head tank creating a constant cycle.

There are in fact two types of vented hot water systems – ‘direct’ and ‘indirect’. How the water is fed into the system or heated (directly or indirectly) is determined by these two terms. A direct heat system relies on immersion heaters to heat the water. These can be single or dual appliances which heat the water at one or two points of the cylinder. An additional way to heat the water is with the use of a separate boiler which is installed specifically for this purpose.

With an indirect heat system, water is heated by a coil fitted inside the cylinder or an immersion heater. Heat to the coil is supplied by the central heating boiler. This heat is transferred from the coil to the water stored in the tank. When the central heating is not working or not in operation, such as in the summer, then an immersion heater can be used to heat the stored water.

Advantages of a vented hot water system:

  • Low maintenance.
  • Cheaper than alternative storage systems.
  • Can be fitted by a plumber or a confident DIYer.

Disadvantages of a vented hot water system:

  • Requires a cold water storage tank (head tank).
  • May require a pump for improved water pressure.

Unvented Hot Water System

This type of set up is fitted in the majority of newly built properties. The reason for this is ease of installation. Unvented systems do not require a head tank, saving on loft space and installation work. The system is connected directly to the rising main allowing for hot water to be supplied directly to the property at mains pressure. To prevent overheating and pressurising, the system should come with an expansion vessel. The water itself can be heated both directly and indirectly with the use of an immersion heater or boiler.

Advantages of an unvented hot water system:

  • Provides hot water at mains pressure.
  • No need for cold water storage or ventilation pipes.
  • Utilises existing pipework.
  • Can be installed anywhere in a property.

Disadvantages of an unvented hot water system:

  • Cannot be used for power showers and some mixer shower valves.
  • Requires specialist installation.
  • Is more expensive than conventional hot water systems.



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