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  • Unvented Hot Water Cylinders

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  • Unvented Hot Water Cylinders

    Updated: July 26, 2023

    What is an unvented hot water cylinder?

    An unvented hot water cylinder is a water vessel which is able to hold heated water under extreme pressure. When a hot water tap or appliance is opened, they can provide instant hot water. There is no need to vent it to the atmosphere because the system is completely pressurised.

    Unvented hot water cylinders have been fitted in households in the UK since the 1980s and have since grown in popularity. They do not require a cold water tank like vented hot water cylinders. That’s why they can be perfect if you don’t have a lot of space. The sealed cylinder will be fed from the cold mains directly. The flow rates and consistency from an unvented cylinder is more reliable due to the fact that the water from the mains enters under high pressure.

    How does an unvented hot water cylinder work?

    The hot water cylinder is directly fed from the incoming mains water supply, which keeps the water under constant pressure and ready to be used. To heat the water within an unvented hot water system there are two different methods.

    The cold mains water is warmed up by an in-built immersion heater in a directly heated model. whereas the water in an indirectly heated model is heated by an external source like a gas boiler or solar panels.

    When hot water is needed by a tap or an appliance, the pressure from the incoming cold water displaces the hot water in the cylinder and carries it along an outlet pipe from the cylinder, taking it to where it is needed.

    Unvented hot water cylinders work best in homes with more than one bathroom or with multiple taps for showers which might be needed at the same time. The high incoming pressure makes it suitable for such homes.

    These systems are equipped with pressure and temperature relief equipments. The aim of these tools is to vent the cylinder in case it overheats or in the event that the internal pressure gets too great. This safety feature is designed to minimise the chances of failing equipments or, in serious cases, the risk of explosion.

    Is an unvented hot water cylinder the right choice?

    Unvented hot water cylinders are a perfect choice for domestic properties. The fact that they do not require a cold water tank makes them especially suited to homes with limited space. The pressure they offer makes them suitable for homes with more than one bathroom. They enable you to run multiple taps and showers at the same time without noticing a drop on the flow rate of the water.

    In recent years, they have gained more popularity and are the ultimate choice for newly-built properties and refurbishments alike. They are ideal for luxury bathrooms with multi-jet showers or jetted baths due to the high water pressure, which they are known for.

    Unvented Hot Water Cylinders
    unvented hot water cylinder

    What is more, they are well suited for places where demand for hot water is high such as hotels, offices, schools and leisure centres. With a large unvented hot water cylinder or multiple ones, your hotel can provide hot water to all rooms during rush hours

    Unvented hot water cylinders are an alternative and a green way of providing hot water. They can be powered by solar panels. The heat can be transformed to the cylinder through a coil. This coil is installed at the base of the especially made vessel.

    What are the advantages of an unvented hot water cylinder?

    Doesn’t require a cold water tank.

    Unvented hot water cylinders are directly fed from the mains. This fact makes them good for homes that have limited space. Another advantage of this is that without a cold water tank in the loft, you will not have to deal with the danger of freezing and bursting of pipes in 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.

    What are the disadvantages of an unvented hot water cylinder?

    If the safety features of your cylinder are not looked after properly, there’s the risk of an explosion. Heated water expands in volume and an unvented system works under high pressure. This is what can cause an explosion.

    There are two ways to ensure the safety of your unvented system. The first is by using what is called a ‘bubble top unit’. This unit produces an internal bubble. The bubble would become trapped at the top of the cylinder to allow the vessel to expand in a safe way. The second method is done by using an external expansion unit which can contain the expanded hot water and prevent it from causing any troubles.

    An unvented hot water cylinder is connected directly to the mains. In case the mains is turned off, your home will be without access to hot water. This can be another disadvantage.

    An unvented hot water cylinder can be more expensive to install than a vented system due to the high pressure they work under. Additional safety features need to be installed such as relief pipework. As a result, this can add to the cost of installation.

    What is the installation cost of an unvented hot water cylinder?

    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?

    It is essential to keep your system serviced and well-maintained. Regular servicing can prolong the lifespan of your cylinder and ensure that it is working efficiently and without troubles. It can also ensure that it is safe to operate and pose no threat to your safety. Your system should be checked once a year by a qualified technician. Reach out to Let’s Heat if you need your system checked and well serviced.

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    How long does an unvented cylinder keep water hot?

    Most hot water cylinder manufacturers suggest that the water will lose between 1 kWh and 2.5 kWh of heat per day. So a 100% full hot water cylinder should stay hot for a day or two.

    Which heating system is better: combi or unvented?

    Combi boilers are often regarded as a heating and hot water cure all, providing more or less instant hot water without the need for a storage and expansion system. However, when specifying for housing where faster flow rates are needed, then an unvented hot water cylinder might be a better option.

    What are unvented hot water cylinders made from?

    Unvented hot water cylinders are usually made from stainless steel, which is a relatively thin and high tensile material. It is capable of expanding with the hot water and withstanding the extreme pressures and high temperatures. Heavy gauge copper is also used as an alternative, but while these might be better for storing hot water, they are also much more expensive as a result.

    Which is better: a vented or unvented system?

    As the mains pressure hot water provided by an unvented system is fed directly from the cold mains, it provides a better pressure performance than a vented cylinder.

    Where should an unvented cylinder be placed?

    An unvented cylinder can be installed anywhere in the home, while a vented cylinder should be located beneath the cold water tank in the attic.

    Do unvented cylinders need servicing?

    Many people are not aware of the fact that an unvented hot water cylinder does require an annual inspection of the key safety devices fitted to the system. You should be aware that the cylinder installed in your property is a pressurised container and will require regular maintenance just like a gas boiler.

    What does installing a new boiler involve?

    If you are renovating, then you don’t have to dig up your floors to install underfloor heating.

    How long does underfloor heating take to warm up?

    An underfloor heating system that is fitted on top of your floors heat up very quickly, whereas a system which is set within a screed might take longer to heat up your home. However, it can retain heat for a longer time and you can also programme it to provide the right amount of required heat.

    Is underfloor heating safe and good for your health?

    Well, underfloor heating is, without a doubt, healthier and safer than radiators since exposed hot surfaces are hidden and dust traps removed. They are a controlled and comfortable heat source, which can help in eliminating draughts and cold spots around your home.