Differences Between Vented and Unvented Hot Water Cylinders

Unsure on the Differences Between Vented and Unvented Hot Water Cylinders?
Below you will see we have given an easy to follow explanation of what each one is and what makes them different.

What is a Vented Hot Water Cylinder?

A Vented Hot Water Cylinder is the more common type of system. They are fed cold water from a header tank which is usually located above the cylinder. They use gravity to deliver the hot water around the home. The cold water can be heated by one of two ways. Either directly by an immersion heater found within the cylinder, or indirectly from an external source such as the central heating boiler. A vent pipe is what links the header tank and the cylinder. When water is heated, it expands and increases in volume. In these systems, expansion is accommodated for in the vent pipe and the header tank

There are a number of advantages to having a Vented Cylinder, these may include;

  • They are less complicated than Unvented systems and therefore much simpler to install
  • They require minimum maintenance
  • This, in turn, also makes them the cheaper option

There are also some disadvantages however, these include;

  • Because the water is fed through a header tank and not from cold water mains, a lower pressure of water is delivered
  • The combination of the cylinder and the header tank means that they take up more room and you don’t have as much flexibility on where you can store them

What is an Unvented Hot Water Cylinder?

An Unvented Cylinder is a pressurised system that has a direct feed from the cold mains supply. While the Vented Cylinder requires a cold water storage tank, the Unvented does not. The water in the cylinder is heated either directly from an immersion heater, or indirectly through the central heating system for example. An expansion vessel must be fitted on unvented cylinders. This is because there is no header tank but the expansion of the water has to be accounted for.

There are a number of advantages to having a an Unvented cylinder, these may include;

  • Having no cold water storage tank means there is more space, as well as more flexibility on where you can store your cylinder
  • They operate at mains pressure meaning they have a better flow rate
  • The system is essentially sealed meaning there is no risk of the water getting contaminated

There are also some disadvantages however, these include;

  • They are more expensive than Vented systems
  • They may also be more complicated and require more maintenance
  • Because they are dependent on the cold water main pressure, if that is turned off for any reason you will be without hot water

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