What is a Direct Unvented Water Cylinder?
A direct unvented water cylinder is a hot water storage cylinder that is connected directly to the mains cold water supply and heats the stored water using electric immersion heaters. It is called “direct” because the water in the cylinder is heated directly by the immersion heater, rather than indirectly via a coil connected to a boiler, heat pump or solar thermal system.
A direct unvented cylinder, unlike a traditional vented cylinder, does not require a cold water storage tank in the loft. Instead, it uses the incoming mains water pressure to deliver hot water to taps, showers, baths and other outlets. When a hot tap is turned on, cold mains water enters the cylinder and pushes the stored hot water out to the outlet. This system can provide excellent hot water pressure provided the property is supplied with a suitable mains water supply.
Direct unvented cylinders are commonly installed in flats, apartments, offices, small commercial premises and homes without a gas, oil or other external heat source. They are also particularly suitable for situations where a simple all-electric hot water system is needed. Many models incorporate one or more immersion heaters that allow the cylinder to heat part or all of the stored water, depending on the design.
Our 80 to 500 litre unvented direct hot water cylinders are listed here – Electric unvented hot water cylinders
An unvented cylinder stores hot water under pressure, so it requires some important safety components. These normally comprise pressure controls, temperature controls, expansion provision, safety relief valves, a tundish and discharge pipework. Installation and servicing should be undertaken by a competent person knowledgeable in unvented hot water systems.
In simple terms, a direct unvented water cylinder is an electrically heated, mains pressure hot water cylinder. It has excellent performance in providing hot water and does not need a loft tank or boiler, but the electrical supply, running costs, cylinder size and safety requirements need to be considered before installation.
