Unvented Cylinders are designed to work directly with water from the mains supply, which makes them suitable for use with System Boilers, that do not have a cold water storage cistern.
Unvented Cylinders are a lot more complicated than vented ones, as they are used in place of the cold water storage, meaning that there are more parts in them.
How do Unvented Cylinders work?
In effect, Unvented Cylinders are like cutting out the middle man in that they store water instead of having a cold water storage point doing it.
The cylinder is powered by the mains pressure, which is why a pump is not needed. The idea is similar to how an emersion heater would heat up water, however the flow of water from the mains is likely to be better than emersion heater could handle.
The cylinder will probably be fitted with safety devices that will help it to deal with the water pressure, as well as the expansion of water.
What are Unvented Cylinders made from?
Designed to have long lifespans, Unvented Cylinders are typically manufactured from Stainless Steel. They are typically fitted with several safety devices including: Pressure Relief Valves and Temperature Controls.
Pros of Unvented Cylinders:
As there is no need for a Header Tank (Cold Water Storage), less space is needed for the overall boiler system.
The lack of Header Tank also means that hot water can be available constantly,
As the Cylinder is not connected to anything other than the boiler, and because it is powered by mains pressure rather than gravity, there is more leeway about where the Cylinder is located.
The Cylinder is powered by mains water, which offers the potential for greater water pressure.
Cons of Unvented Cylinders:
Unvented Cylinders are complicated, which means that there is more to go wrong and it is a more complex procedure to try and fix it.
The complexity of their design, also means that Unvented Cylinders are very expensive to install and fit, as well as maintain.
They can also be expensive to run, as they tend to be powered by electricity.
Unvented Cylinders are not suitable for use with power showers and some mixers.
You should always consult a qualified Heating Engineer before making any final decisions about purchasing a hot water cylinder.