What Is an Open-Vent Heating System?

Written by andrea stein
  • Share
  • Tweet
  • Share
  • Pin
  • Email
What Is an Open-Vent Heating System?
An open-vent heating system automatically manages the radiator water supply level. (white radiator image by Ekaterina Sidorenko from Fotolia.com)

An open-vent heating system refers to a system that contains a header tank used to keep the radiator system and boiler topped off with water. Open-vent heating system uses different heating methods than sealed systems.


Open-vent heating systems contain a float valve in the tank which connects to the main water and is used to keep the water level in the tank correct. Water heats as it rises to the top of the cylinder, enabling it to be drawn off through hot water taps or shower outlets.


Advantages of open-vent heating systems over sealed heating systems include automatically-topped off water levels, without the human intervention needed in sealed systems. Sealed systems use an expansion vessel as opposed to a header tank, which is fitted with a compressible air bladder. Expansion vessels can malfunction due to bladder leakage, and are not always able to accommodate increases in volume of heating system contents, leading to system pressure loss.


Open-vent heating system usage requires sufficient attic space, which can be problematic in smaller homes. The header tank must also be positioned higher than the cylinder, but must still be accessible, and must possess a continuous route to the outside for the overflow pipe. Sealed heating systems do not require such specific positioning.

Don't Miss

  • All types
  • Articles
  • Slideshows
  • Videos
  • Most relevant
  • Most popular
  • Most recent

No articles available

No slideshows available

No videos available

By using the eHow.co.uk site, you consent to the use of cookies. For more information, please see our Cookie policy.