Unvented water cylinders receive water directly from the mains whereas vented water cylinders receive water from external water tanks stored in loft space.
As unvented water cylinders receive water directly from the mains, it benefits from greater levels of pressure, distributing water easily throughout your home.
They do not require a separate cold water tank, making them more compact than other systems which require loft space.
Vented water cylinders receive water from external cold water tanks which are typically stored in the loft. They are found in the loft as they rely on gravity to build pressure, rather than having the pressure generated from the mains.
It is called a vented hot water cylinder because a vent pipe is used to connect the hot water tank to the header tank.