Hot Water Cylinders

Energy Saving Trust recommend hot water cylinders that have been factory insulated to help keep your hot water at the right temperature for longer.

Upgrading your hot water cylinder to an Energy Saving Trust Recommended one can save you around £40 a year. They are already highly insulated and help you save the most energy and money.

Types of Hot Water System

Hot water systems in the UK generally fall into these basic types

  • With hot water storage cylinders(usually in the airing cupboard)
    • Vented hot water cylinder (with cold water tank in the loft)
    • Unvented hot water cylinder (no cold water tank)
  • Combi boiler with hot water on demand direct from boiler (no hot water  storage system)

These can be supplemented by the new eco-technologies such as Solar Hot Water Systems and Ground Source Heat Pumps.

For help selecting the right sort of Hot Water System for your home call Steven Banks on 01462 636376

Vented hot water cylinder system

This is the traditional hot water system found in most UK households and is a low pressure system.

There is a cold water storage tank (header tank) in the loft and a copper hot water cylinder in the airing cupboard. Water in the cylinder is topped up from the header tank in the loft which in turn is kept topped from the mains. Water in the cylinder is heated either by an electric immersion heater  (direct) and/or by the central heating boiler (in-direct). Hot water in the cylinder is used to supply the hot taps.

The header tank also acts as an expansion tank, as the water in the hot water cylinder heats up it expands and excess goes back to the header tank and a vent allows trapped air to escape to prevent  build-up of pressure.

vented water cylinder

Hot water pressure and showers:

Hot water pressure is governed by the height of water in the tank above the tap or shower being fed. Typically this gives reasonably good pressure at taps on the ground floor in the kitchen but lower pressure upstairs in the bathroom. Hence bathroom showers run straight off the hot water cylinder are usually problematical. So for showers the usual solution is to fit some sort of pump or a self-contained shower that heats water on demand.

Unvented hot water cylinder system

An unvented system consists of a pressurised hot water cylinder fed directly from the mains water supply. It supplies hot water at cold water mains pressure to taps and showers.

unvented water cylinder

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.

To allow the water that is heated in the cylinder to expand as it is heated, an expansion vessel is used and the system includes a pressure relief valve.

Benefits of Unvented Hot Water Cylinders:

  • Hot water flows at cold water mains rates – a substantial improvement over vented systems and compared to a condensing combi boiler.
  • More flexibility over where the cylinder is installed space – an unvented cylinder can be installed anywhere (for example in a garage) freeing up space in the airing cupboard and there is no need for header tank in loft.
  • No risk of frozen pipes in the cold loft in winter.

Disadvantages of Unvented Hot Water Cylinders:

  • Hot water flow depends on cold water mains pressure – so if the cold water goes off you also loose hot water. With a vented system hot water would still be available from the hot water cylinder until it ran out.
For help selecting the right sort of Hot Water Cylinder for your home call Steven Banks on 01462 636376