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To install a cylinder wrap you need to have good access to the cylinder. You will need at least 5 cm all around the cylinder - more will make the installation easier. If you have easy access to the cylinder, installing a wrap is not difficult and take about two hours. Don't forget to install pipe-lagging insulation to at least the first metre of hot water pipe that comes out of the cylinder, as this will also save you money.
There are different brands of cylinder wraps on the market. As the size may vary, make sure the wrap is the correct size for your cylinder.
The insulation value of wraps may also vary. The R-value gives an indication of the insulation value of a wrap: the higher the R-value, the more heat retained. Not all wraps have the insulation value marked on the packaging though. The following table gives the R-value of the different brands that are known to Environment Canterbury.
In older houses, with a direct system, the hot water may be stored in a square galvanised tank. The principle is the same. Using the diagram above as a reference, another cold water pipe runs from the base of the cylinder to the boiler. The boiler heats the water and returns it to the tank higher up. When hot water is drawn from the tank, it is replaced by cold from the cold tank, which in turn is fed to the boiler. This is direct heating of the water by either a) the immersion or b) the boiler. The hot water is simply stored in the tank.