Another common question we often come across from our customers who want to upgrade their hot water system is whether to install a vented or unvented hot water cylinder.
In short an unvented system feeds water from the mains directly into the hot water cyclinder, whereas a vented system feeds water from the mains into a cold water storage tank and from here the water feeds into the hot water cylinder.
Untill 1989 only vented cylinders were used in domestic central heating systems. In a vented system the appliances requiring hot water are fed indirectly via the cold water storage tank, which is generally stored in the loft, to the water cylinder and heated using a heat exchanger. Because the water supply is gravity-fed it provides less water pressure.
However as the unvented system feeds directly into the hot water cylinder it has much higher water pressure, which can be controlled using in built safety devices that are designed to deal with this pressure.
In terms of what the advantages and disadvantages are - a vented system is easier and cheaper to install. However it does require a cold water storage tank, which takes up more space and the water pressure is much lower.
The advantages of the unvented system are that it supplies hot water at mains pressure and because it does not require a cold water storage tank it can be sited in any location within the house. However it can be trickier and more expensive to install and doesn't always work well with some power showers and mixers.
So all in all whether you decide to go with a vented or unvented hot water cylinder, it all comes down to: