An unvented cylinder is a type of domestic hot water storage tank that is supplied directly by the cold water mains, providing high mains pressure to taps and showers, and eliminating the need for a cold water feed tank. As a sealed, unvented system, it requires an expansion vessel to manage pressure increases from heating water and relies on a G3 qualified engineer for installation and yearly maintenance. The water is heated by either an immersion heater (direct model) or an external heat source like a boiler or heat pump (indirect model).
How it Works
- The cylinder is fed directly from the mains cold water supply, which is already pressurised.
- Water is heated either by an immersion heater inside the cylinder (direct system) or by a heat exchanger connected to an external boiler or solar thermal system (indirect system).
- When a hot water outlet is opened, the pressure from the incoming cold water pushes the heated water out of the cylinder and to the tap or shower.
- Because the system is sealed (unvented), an expansion vessel is necessary to absorb the expanded volume of water as it heats, preventing excessive pressure build-up.
- The system includes pressure relief valves and combination valves as safety features to control and relieve excess pressure.
Key Benefits
- Delivers mains pressure at outlets, resulting in better performance from taps and showers.
- Does not require a separate cold water storage tank, reducing space requirements.
- Can be installed in various locations where a tank-fed system might not be suitable.
- Unlike open-vented systems, it is less prone to contamination and freezing.
Components
- Inner Stainless Steel Tank: Stores the hot water.
- Insulation: A layer of foam insulation minimizes heat loss.
- Expansion Vessel: A crucial component that accommodates the expansion of water as it heats.
- Pressure Relief Valve & Combination Valve: Safety devices to manage and relieve system pressure.
- Immersion Heater (for direct systems): An electrical element that directly heats the water.
