Unvented Hot Water System

Unvented hot water system

Unvented hot water systems are a well-liked as a reliable source of hot water for home or commercial use. An unvented hot water system uses the mains water pressure to pressurise the system and deliver a high flow rate of hot water to all of the outlets throughout the property. We’ll discuss the advantages of an unvented hot water system in the following article, including their effectiveness, safety, and usability.

Unvented cylinders come in direct and indirect versions. In contrast to an indirect unvented cylinder, indirectly heating the hot water cylinder via a traditional gas or oil boiler or a heat pump heating system, a direct unvented hot water cylinder employs immersion heaters to heat the hot water cylinder directly with electricity.

Unvented hot water systems- How do they work

As they are fed directly from the cold-water mains, unvented cylinders operate at mains pressure.

An unvented system is a closed or sealed system and therefore requires additional devices, such as an expansion vessel, for controlling the pressure changes within the hot water system as the water inside the hot water cylinders heats up, as water is essentially incompressible.

Expansion vessel in unvented systems

Since water expands when heated, it is necessary to account for this expansion. To facilitate this, an expansion vessel must be attached somewhere within the hot water cylinders system. It may be affixed to the cylinder, connected to the hot water system elsewhere, or even integrated into the cylinder.

Efficiency is one of the key advantages of an unvented hot water cylinder. The water is heated and kept at a higher temperature than in vented cylinders because the system is pressurised. This makes it perfect for larger families or homes with multiple bathrooms since it allows for a significantly higher flow rate of hot water to feeding multiple outlets such as your home’s taps and showers, something that a combi boiler will struggle to achieve.

Additionally, the water can be heated more quickly by using a backup immersion heater or immersion heaters in the system, which cuts down on the time it takes for the water to reach the appropriate temperature. The need for frequent heating is decreased by the use of a thermostat which also keeps the water at a steady temperature.

Unvented hot water cylinder

Safety is another another key advantage of unvented hot water cylinders. A cold water tank in the loft is not necessary because the system is pressurised; nonetheless, this can provide a safety risk in the event of a leak or flooding. A safety valve and expansion vessel are also included in the system to guarantee that any excess pressure or temperature is discharged safely via a tundish, preventing system damage to the unvented system.

Easy of use

Unvented hot water systems are also exceedingly simple to operate. The pressurised system results in substantially higher water pressure at the taps and showers than in a conventional vented cylinder, making it quicker and easier to use multiple outlets such as taps and showers. But please note the hot water pressure will only be as good as your incoming cold water mains pressure when using unvented cylinders or a unvented system.

Showering experience is improved with stronger water pressure, from the mains water supply when utilizing an unvented system. Additionally, since there isn’t a cold water tank, frequent maintenance and cleaning aren’t necessary, which saves time and maintenance costs in keeping the system in good operating order as opposed to vented cylinders

Unvented cylinders or an unvented hot water tank can also be installed in a number of places throughout the property, including loft areas or basements, since it is pressurised by mains pressure cold water and does not rely on natural gravitational force / gravity to provide hot water. This gives homeowners more freedom in deciding where to place the unvented cylinder, which can be very advantageous in homes with limited or less space, unlike vented cylinders which need piped access to loft tanks.

Our range of unvented cylinders

The best hot water cylinders must be able to store water under pressure, so they must be durable and as corrosion-resistant as possible. We do a couple of ranges – first our domestic or light commercial range, with cylinder capacity from 80 to 500 Litres ,which are manufactured in duplex stainless steel, which is generally considered a highly corrosion resistant material. There are two options for these mains pressure unvented systems range

Direct unvented hot water cylinders range –

These are fully detailed on this webpage – unvented direct cylinders

Or our

Indirect unvented hot water cylinders

These indirect units , which are installed alongside a boiler or heat pump to feed the coil in the cylinder, having a high heat recovery rate when compared to the direct cylinder range , again with cylinder model sizes from 80 to 500 Litres – these are detailed here –unvented indirect hot water cylinders

We also do a commercial range from 200 to 6,000 Litres in size, which are available as glass lined mild steel or stainless steel vented and unvented cylinders. These are detailed on this webpage – commercial indirect hot water cylinder range

Installation and maintenance of unvented hot water cylinders

Unvented cylinders should come equipped with additional safety measures to protect them against overpressure, such as a pressure-reducing valve to restrict the cold incoming water supply pressure entering the water heating system and a temperature and pressure relief valve are also installed on unvented cylinders for further security, to release the domestic hot water if it becomes too hot.

An unvented hot water system must be installed by a licenced heating engineer (the heating engineers / plumbers need to be certified in building regulations “G3” unvented hot water systems, which covers the safety regulations of an unvented system) , but once they are, they require very little upkeep. The pressure relief valve, thermostats and expansion vessel on any unvented cylinder should be checked annually to make sure they are functioning properly, but other than that, not much more needs to be done to an unvented hot water cylinder.

Unvented cylinder

The system is also significantly more energy-efficient than a vented cylinder due to the use of an immersion heater or heating element, which lowers energy costs and the amount of energy needed to heat the water. In addition, there is less chance of bacterial growth in the system because the water is heated and kept at a higher temperature, which further lowers the need for maintenance.


In conclusion, unvented cylinders have many advantages over vented systems, including increased effectiveness, enhanced safety, and simplicity of operation. These systems are also more energy-efficient and low-maintenance than conventional systems due to the removal of a cold water tank and the use of an immersion heater or heating element. A property, be it domestic or commercial with an unvented hot water system may be the best option if you’re thinking of improving your hot water system.