Difference Between Vented and Unvented Hot Water Cylinders

When we speak about hot water cylinders, we generally come across two terms – vented and unvented. It is important to know the difference between them so that an informed choice can be made. In the subsequent sections, we take a look at either of them to determine what can be expected from both of them.


  • A Vented System – In a vented hot water cylinders system, there will be a storage tank overhead that contains cold water in it. This type of solution is more of a traditional approach of heating water as the overhead tank supplies water to the hot water cylinder.

The heating may take place either by an immersion heater in the cylinder or through the solid fuel appliance or even the central heating boiler.

The overhead water tank that carries the cold water helps the trapped air in escaping out, and it also works as an expansion tank for the water as it expands during the heating process. In cases of overheating conditions too, the tank can be very useful.

  • Some pros and cons of this system – Some advantages and disadvantages of the system are discussed here as under.

Pros РSince this type of hot water cylinders work at low pressures and are very simple construction-wise, they are quite cheap and economic. The best part is that they hardly need any type of maintenance.

Cons – The biggest problem while working with them can be lower water pressure at most times. Moreover, the system will require considerable space for the cold water tank as well as the hot cylinder.

  • An Unvented System – Unwanted hot water cylinders form a pressurized system that is delivered directly from the mains water line and supplies water at a very high pressure that can be suitable for bathing and all other types of functions. This type of system does not need a storage water tank in the loft or at any other place. Therefore, considerable space saving can be done. Water in it can be heated in many ways – using a central heating system, immersion heater, renewable energy sources like biomass, solar, etc. Many fuel sources can also be connected to it depending upon preference.
  • Some pros and cons of the system – Some of the pros and cons are discussed here.

Pros – It does not need a bulky overhead tank for storing cold water. High pressurized water can be available at all times.

Cons – Water expansion vessels may have to be fitted in it to deal with the expansion of water as it gets heated. This type of hot water cylinders needs servicing at definite periods of time so that they can work seamlessly.

We have seen here both types of the hot water system that are prevalent in the market today. Depending upon one’s use, utility and preference, either of them can be chosen for a property although it is very much clear that the Unvented system is more preferred over the other one.