Open Vented Cylinders Open Vented (Standard) cylinders
An Open Vented cylinder is the most common means of providing hot water in the home, this is a copper hot water storage cylinder which is fed from a cold water storage tank. This arrangement falls into three types. Separate ColdWater Tank, Combination Unit and Primatic Cylinder.
The hot water flow rate from the taps depends on the height of the cold water tank (CWS), and the bore of the pipes, the higher the tank above the cylinder (termed head), the better the flow rate.
The cylinder is usually located in the airing cupboard, it may be heated with an electric immersion heater or from a boiler. It is usually cheaper to heat your hot water with a gas boiler (indirectly) than using the electric immersion heater. Some cylinders (direct) only have electric immersion heaters, these are normally heated on a timed lower rate electricity tariff.
If the indirect hot water cylinder is heated from a boiler, it may be by gravity circulation, usually found on older installations, or if modern it may be fully pumped. If you are considering replacing your hot water cylinder and it is currently heated by gravity circulation, then it should be upgraded to a fully pumped system, with a factory insulated high recovery cylinder, such as the Range or Albion hot water cylinders.
A Combination Unit or Fortic type hot water cylinder has a cold water tank directly above the hot water storage, all the pipe work is pre-connected.
A Primatic Cylinder is not commonly used, but can accommodate the expansion from the heating system within the hot water compartment, this eliminates the need for a separate feed and expansion tank.