Vented & Unvented Water Cylinders

Unvented hot water systems

These systems have no cold-water storage tank

Unvented hot water cylinders were only made legal in the UK in the 1980’s but have since rapidly grown in popularity. In an unvented system there is no cold-water tank – instead the sealed hot water cylinder is fed directly by the cold water mains. Since they are operating at mains pressure, they offer much better flow rates meaning your shower and bath performance should be higher.

The other major benefit is that you don’t need to maintain a cold-water tank in the loft (which vented systems require). This is good news since not only does it free up space, it also removes the potential freezing issue during our long cold winter periods.

In addition, since you aren’t relying on gravity to move the hot water around the home, the unvented cylinder can be located pretty much anywhere in your property.

Other advantages of installing an unvented system include reduced noise in the system since there is no cold water filling of the water storage cistern, and since there is no water storage cistern and the system is essentially sealed, the cold water is not at risk from contamination.

Vented hot water systems

These systems are fed from a header tank

Vented hot water tanks are still the most common type of hot water systems found in the UK. Unlike the newer unvented tanks, these copper tanks are fed by cold water from a header tank (normally located in the loft) and they use gravity to drive the hot water around the home. A vent pipe links the vented hot water cylinder and the cold water in the header tank.

As with the unvented system, expansion of warm water is still an issue, but in this case the expansion simply takes place via the vent pipe and in the header tank.

The hot water pressure tends to be governed by the height of the water tank above the tap or shower feed, which means that although on the ground floor of the home the pressure might be excellent – in rooms on upper floors the pressure will be lower. As a result many showers in homes with vented hot water tanks use electric pumps to drive the hot water to the shower at increased pressure.

Vented hot water cylinders are far less complicated than the pressurised vented systems and for this reason they are much simpler to maintain and install – making them a far cheaper option when compared to the unvented system.