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  • Unvented Hot Water Cylinders

    Updated: April 14, 2024

    What is an unvented hot water cylinder?

    An unvented hot water cylinder is a pressurized water container designed to hold heated water, ensuring instant hot water supply when a tap or appliance is activated. Unlike vented cylinders, they operate without the need for venting to the atmosphere.

    Since their introduction in UK households in the 1980s, unvented hot water cylinders have gained popularity. Their space-saving design eliminates the need for a cold water tank, making them ideal for properties with limited space. Directly fed from the cold mains, these sealed cylinders offer reliable flow rates and consistent performance, as water enters under high pressure, ensuring efficient operation.

    How does an unvented hot water cylinder work?

    Unvented hot water cylinders are directly connected to the mains water supply, ensuring a constant pressure for immediate use. There are two primary methods for heating the water within these systems:

    In a directly heated model, an in-built immersion heater warms the cold mains water within the cylinder. Conversely, in an indirectly heated model, an external source such as a gas boiler or solar panels heats the water.

    When hot water is required at a tap or appliance, the pressure from the incoming cold water displaces the hot water in the cylinder, directing it through an outlet pipe to the desired location.

    Unvented hot water cylinders are particularly effective in homes with multiple bathrooms or numerous taps requiring simultaneous usage, thanks to their high incoming pressure.

    Equipped with pressure and temperature relief mechanisms, these systems prioritize safety. These devices are designed to release pressure and vent the cylinder if it overheats or the internal pressure becomes too high, minimizing the risk of equipment failure or, in extreme cases, explosion.

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    Is an unvented hot water cylinder the right choice?

    Unvented hot water cylinders offer an ideal solution for residential properties, particularly those with limited space, as they eliminate the need for a cold water tank. Their high pressure capability makes them suitable for homes with multiple bathrooms, allowing for simultaneous use of taps and showers without any noticeable drop in water flow.

    In recent years, they have surged in popularity and are the preferred choice for both new constructions and renovations. Their ability to deliver high water pressure makes them perfect for luxurious bathrooms featuring multi-jet showers or jetted baths.

    Furthermore, they are well-suited for environments with high hot water demand, such as hotels, offices, schools, and leisure centers. By utilizing a large unvented hot water cylinder or multiple units, hotels can ensure ample hot water supply to all rooms during peak hours.

    Unvented hot water cylinders also offer an eco-friendly alternative for hot water provision, as they can be powered by solar panels. Heat from solar panels can be efficiently transferred to the cylinder through a coil installed at the base of the specially designed vessel.

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    Doesn’t require a cold water tank.

    Unvented hot water cylinders, supplied directly from the mains, are ideal for homes with restricted space. Additionally, their design eliminates the need for a cold water tank in the loft, mitigating the risk of pipe freezing and bursting during winter.

    Consistent flow of hot water

    The flow rate with an unvented system is much better than that of a vented one. You will get to enjoy a better flow rate as well as better performance from your hot taps and showers. This can also be ideal for luxury bathrooms with jetted baths.

    Can be sited anywhere in your home

    Unlike vented systems which rely on gravity to transport hot water around, an unvented system requires no such thing. They use high pressure to move water around your house. As a result, they can be located in any suitable place.

    Quiet performance

    Unvented hot water cylinders are much quieter than vented systems. This is possible due to the absence of a cold water tank, which can be noisy while filling up. In addition, a sealed unvented system means there is no risk of cold water being contaminated.

    A green alternative

    Certain specially designed unvented tanks can be connected to a solar panel system. This can reduce your carbon footprint.

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    What are the disadvantages of an unvented hot water cylinder?

    What are the disadvantages of an unvented hot water cylinder?

    If the safety precautions of your cylinder are neglected, there is a potential risk of explosion. Due to the expansion of heated water and the high pressure of unvented systems, such an explosion can occur.

    There are two methods to ensure the safety of your unvented system. The first involves using a ‘bubble top unit’, which generates an internal bubble that safely accommodates the expansion of the vessel. The second method utilizes an external expansion unit to contain the expanded hot water, preventing any potential issues.

    Connecting directly to the mains, an unvented hot water cylinder means that if the mains supply is shut off, your home will be deprived of access to hot water, posing another drawback.

    Installation of an unvented hot water cylinder can be pricier compared to a vented system due to the higher pressure they operate under. Additional safety features, like relief pipework, need to be installed, consequently increasing installation costs.

    As has been said before, an unvented hot water cylinder can be more expensive than a vented system because of the additional safety features that must be installed. This high cost ensures that you are kept safe and that your system is fit to run smoothly.

    In short, an unvented hot water cylinder can cost between £400 to £1600+, depending on different factors such as the size, brand, if you already have a cylinder installed and if you need to move your system.

    An unvented hot water cylinder can be a great investment if installed properly and with the required safety measures. They can last for years and provide instant hot water to your taps and showers.

    Do unvented hot water cylinders need servicing?

    Maintaining your system is crucial for its longevity and efficient operation. Regular servicing not only extends the lifespan of your cylinder but also ensures its safe and trouble-free operation. It is recommended to have your system checked annually by a qualified technician to guarantee its safety and efficiency. If you require servicing for your system, feel free to contact Let’s Heat for professional assistance.

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    How long does an unvented cylinder keep water hot?

    According to most hot water cylinder manufacturers, the heat loss typically ranges from 1 kWh to 2.5 kWh per day. Therefore, a fully filled unvented hot water cylinder can keep water hot for approximately one to two days.

    Which heating system is better: combi or unvented?

    Combi boilers are often seen as a versatile solution for heating and hot water needs, offering instant hot water without the necessity for a storage system. However, in scenarios requiring higher flow rates, such as certain housing specifications, an unvented hot water cylinder may be a more suitable choice.

    What are unvented hot water cylinders made from?

    Unvented hot water cylinders are commonly constructed from stainless steel, a durable and expandable material capable of withstanding high temperatures and pressures. Alternatively, heavy gauge copper is sometimes used, offering superior heat retention but at a higher cost.

    Which is better: a vented or unvented system?

    Unvented systems, providing hot water directly from the mains, typically offer better pressure performance compared to vented cylinders.

    Where should an unvented cylinder be placed?

    An unvented cylinder can be installed anywhere within the home, whereas a vented cylinder is typically located beneath the cold water tank in the attic.

    Do unvented cylinders need servicing?

    Despite common misconceptions, unvented hot water cylinders necessitate annual inspections of safety devices to ensure proper functioning and safety. As pressurized containers, they require regular maintenance akin to gas boilers.

    What does installing a new boiler involve?

    In renovation projects, underfloor heating can be installed without the need for disruptive floor excavation.

    How long does underfloor heating take to warm up?

    The heating time of underfloor systems varies; surface-mounted systems heat up quickly, whereas those set within a screed may take longer. However, they retain heat for an extended duration and can be programmed for precise heating control.

    Is underfloor heating safe and good for your health?

    Underfloor heating offers a safer and healthier alternative to radiators, as it eliminates exposed hot surfaces and reduces dust accumulation. It provides controlled and comfortable heat distribution, minimizing draughts and cold spots throughout the home.