The quest for efficient and cost-effective heating solutions in the UK has seen the emergence of a variety of systems, with the Unvented Hot Water Cylinder standing out due to its unique features and benefits.

This article aims to take you through a detailed journey of understanding what unvented hot water cylinders are, their benefits, cost of installation, and the importance of professional handling. Whether you’re a homeowner, a landlord, or simply a curious individual, this guide provides insights into why you might want to consider unvented hot water cylinders for your heating needs.

Understanding Unvented Hot Water Cylinders

Traditionally, UK homes were equipped with heat-only boilers connected to copper cylinders and cold water tanks. However, with the advent of combi boilers, which offer instant hot water and require less space, the popularity of the traditional setup began to wane.

Combi boilers have indeed become a favourite for many homeowners and landlords due to their efficiency and space-saving characteristics. However, they may not be the most suitable solution for larger properties, particularly those with multiple bathrooms. Enter the unvented hot water cylinders, which present an alternative solution for such properties.

Unvented hot water cylinders are often constructed from stainless steel, making them more resistant to corrosion, especially in hard water areas. This is a considerable advantage over the older copper cylinders. Moreover, unvented cylinders come with a built-in insulation layer, enhancing their energy efficiency.

This feature not only makes them compatible with gas boilers but also allows them to work efficiently with Heating Interface Units (HIU), solar panels, and air source heat pumps. Additionally, these cylinders are connected to mains pressure, which, when installed and balanced correctly, can provide uninterrupted hot water to multiple outlets, allowing simultaneous shower or bath usage.

Difference between Vented Cylinders and Unvented Cylinders

Hot water cylinders are a crucial component of a home’s heating system, providing a way to store and distribute hot water throughout the property. There are two main types of hot water cylinders: vented and unvented. Each has its own advantages and disadvantages, and the best choice for your home will depend on various factors such as your household’s hot water demand, available space, and existing heating system. The choice between a vented and unvented cylinder will depend on your specific needs and circumstances. If space is at a premium and you want higher water pressure, an unvented cylinder could be the best choice. However, if cost is a major concern a vented cylinder may be more suitable

Vented Cylinders

Vented cylinders, also known as regular or conventional cylinders, are the traditional type of hot water cylinder. They are connected to a large cold water storage tank, usually located in the loft, which supplies water to the cylinder. The cylinder then heats the water, either using heat from a boiler or an electric immersion heater, and stores it until it’s needed.

The pressure of the hot water from a vented cylinder relies on gravity, with the height of the water tank above the outlets determining the pressure. This can mean that the water pressure is lower than with an unvented system, especially in properties where the water tank is not much higher than the outlets.

One of the main disadvantages of vented cylinders is that they require a cold water storage tank, which can take up a lot of space. This can be a particular issue in smaller properties or those without a loft. However, vented cylinders are generally cheaper to install and maintain than unvented cylinders, and they don’t require the same level of safety equipment.

Unvented Cylinders

Unvented cylinders are a more modern alternative to vented cylinders. They take their water supply directly from the mains, eliminating the need for a cold water storage tank. This can save a significant amount of space and also means that the hot water pressure is typically higher and more consistent than with a vented system.

Unvented cylinders heat the water in the same way as vented cylinders, either using a boiler or an electric immersion heater. However, because they operate at mains pressure, they require additional safety features, such as a pressure relief valve and an expansion vessel, to prevent over-pressurisation.

While unvented cylinders offer several advantages, they are more expensive to install and maintain than vented cylinders. They also need to be installed by a qualified professional, as incorrect installation can lead to serious safety issues.

The Advantages of Installing Unvented Hot Water Cylinders

There are several reasons why homeowners and landlords alike are opting for unvented hot water cylinders. Here are the key benefits of installing these units:

1. Direct Mains Connection: Unvented cylinders take water directly from the mains, eliminating the need for a tank in the loft.
2. High Water Pressure: Mains water typically has better pressure than loft tanks that rely on gravity, which improves the performance of showers and taps.
3. Reduced Risk of Freezing: By removing the tank from the loft, you significantly reduce the risk of freezing in the winter, enhancing the reliability of your heating system.
4. Simultaneous Water Supply: A correctly installed unvented cylinder allows uninterrupted hot water supply to multiple outlets at the same time, perfect for households with multiple bathrooms.
5. Compatibility with Renewable Energy Sources: Unvented cylinders can be used with solar thermal panels to heat water, reducing heating bills and carbon footprint.
6. Flexible Installation Options: Unlike conventional cylinders, unvented cylinders can be installed anywhere in the home due to their direct connection to the mains.
7. Water Safety: Unvented cylinders are part of a sealed system that prevents water contamination, thus ensuring the safety of your water supply.

How does an unvented cylinder work

An unvented hot water cylinder operates slightly differently from a conventional vented hot water system. Here’s a simplified explanation of how an unvented cylinder works:

• Direct Water Supply: In an unvented system, the hot water cylinder is directly connected to the mains water supply, which fills the cylinder with cold water.
• Heating the Water: The cold water in the cylinder is then heated by a heat source. This could be an immersion heater within the cylinder or an external source such as a boiler or solar thermal panels. The heated water then expands. However, unlike in a vented system, the excess pressure cannot be relieved by a vent pipe leading to a tank; it must be accommodated within the system.
• Pressure Release: To handle the increased pressure of the heated water, unvented cylinders are equipped with safety devices. The most notable is an expansion vessel, which contains a pocket of air that compresses to accommodate the extra volume of water as it expands. This keeps the pressure in the system at a safe level.
• Water Distribution: When a hot water tap is opened in the house, the pressure from the mains supply pushes the hot water out of the cylinder and towards the outlet, such as a shower or tap.
• Safety Measures: Additional safety devices are installed in unvented systems to handle exceptional circumstances. These include a temperature and pressure relief valve, which will release water from the system if the temperature or pressure becomes too high, and a tundish, which allows you to see if any water is being released, indicating a problem with the system.

It’s important to note that unvented hot water systems need to be installed and serviced by a certified professional, due to the high pressures and temperatures involved. They must comply with building regulations and, when installed correctly, they can provide high performance and safe hot water delivery

Is an Unvented Hot Water Cylinder the Right Choice for you?

Choosing the right hot water system for your home is a crucial decision that can impact your comfort, energy bills, and the space usage in your property. If you’re considering replacing your traditional regular boiler and vented cylinder an unvented cylinder could be a suitable option. However, whether it’s the right choice for you will depend on various factors, including the size of your property, the number of radiators and bathrooms, and your household’s hot water demand

Combi Boiler for Smaller Properties

For smaller properties with fewer than 10 radiators and one bathroom, a combi boiler could be an excellent choice. Combi boilers are compact all in one units that provide both hot water and central heating on demand, eliminating the need for a separate hot water cylinder or a cold water storage tank.

One of the main advantages of combi boilers is that they can save a significant amount of space. Since they heat water directly from the mains when you turn on a tap there’s no need for a hot water storage cylinder making them ideal for smaller properties where space is at a premium.

Another advantage of combi boilers is that they can provide hot water at mains pressure, which can result in a better performance from your shower and other hot water outlets. However, combi boilers may struggle to provide hot water to multiple outlets simultaneously, which is something to consider if you often use several hot water outlets at the same time.

System Boiler with Unvented Cylinder for Larger Properties

For larger properties with more than 10 radiators, two or more bathrooms, and a high hot water demand, a system boiler with an unvented cylinder is usually the best option. System boilers heat your central heating system directly and produce hot water for your cylinder.

An unvented cylinder can provide a large amount of hot water to multiple outlets at the same time, making it ideal for larger households. Since it’s connected directly to the mains, it can deliver high water pressure, improving the performance of your showers and other hot water outlets.

Unvented cylinders also eliminate the need for a cold water storage tank, saving space in your loft. However, they are larger than combi boilers and do require a suitable space for installation.

In conclusion, whether an unvented cylinder is right for you will depend on your specific needs and circumstances. It’s always a good idea to consult with a heating professional who can assess your property and advise you on the best solution for your needs.

Compliance with Building Regulations and G3 Qualifications 

The installation of unvented hot water systems is a task that requires specific knowledge and expertise. In the UK, it’s mandatory that this type of work is carried out by a professional who holds a G3 qualification. The G3 qualification is a specific certification that demonstrates the engineer has been trained in the installation, commissioning and servicing of unvented hot water systems.

The G3 qualification is not just a recommendation but a legal requirement. This is due to the potential safety risks associated with incorrectly installed unvented systems. These systems operate under high pressure and have specific requirements for things like discharge pipes and pressure relief valves as part of their safety system.. An incorrectly installed system could potentially fail leading to serious consequences such as water damage, scalding or in extreme cases an explosion

In addition to the requirement for a G3 qualified engineer any installation of an unvented hot water system must be notified to the local Building Control Department. This is a requirement under Part G of the UK Building Regulations, which covers sanitation, hot water safety and water efficiency. The Building Control Department is responsible for ensuring that all building work including plumbing and heating installations, complies with the Building Regulations.

When an unvented hot water system is installed the engineer will notify the Building Control Department who may then choose to inspect the work to ensure it complies with the regulations. Once they are satisfied, they will issue a building regulation compliance certificate. This certificate is important and should be kept safe as it may be required for future reference for example if you decide to sell your property.

The Importance of Insulation in Unvented Hot Water Systems

Insulation plays a crucial role in the efficiency and performance of unvented hot water systems. A well-insulated hot water cylinder will retain heat for longer, reducing the amount of energy required to keep the water at the desired temperature. This can result in significant energy savings and lower heating bills

Insulation in unvented hot water systems is not just about energy efficiency, though. It also plays a role in safety. The high temperatures inside the cylinder could potentially cause burns if the outside of the cylinder was not adequately insulated

Modern unvented hot water cylinders come with factory fitted insulation, usually in the form of a foam-like material that covers the outside of the cylinder. The thickness and type of insulation can vary, but it’s generally designed to provide the best possible balance between heat retention and safety.

Difference between Direct and Indirect Unvented Hot Water Cylinders

Direct and indirect unvented cylinders are two types of hot water storage systems that operate at mains pressure. The key difference between the two lies in the way they heat the water.

Direct Unvented Cylinders

Direct unvented cylinders heat the water directly within the cylinder itself. They use one or more electric immersion heaters, which are located inside the cylinder, to heat the water. When the immersion heater is switched on, it heats the surrounding water. This type of cylinder does not rely on any external source of heat, such as a boiler or solar panels

Direct unvented cylinders are often used in properties that do not have a central heating system, or where it’s not practical to connect the cylinder to a boiler. They can also be used as a backup source of hot water in case the boiler fails.

Indirect Unvented Cylinders

Indirect unvented cylinders, on the other hand, are heated by an external source, usually a central heating boiler, but it could also be solar thermal panels or a heat pump. The hot water from the boiler (or other heat source) circulates through a coil of pipe inside the cylinder, transferring its heat to the water stored in the cylinder

Indirect cylinders have the advantage of being able to provide large amounts of hot water quickly, as they can take advantage of the high output of a boiler. They are typically more energy-efficient than direct cylinders, especially if they are connected to a high-efficiency condensing boiler or a renewable heat source

The choice between a direct and indirect unvented cylinder will depend on the heating system in the property, the amount of hot water required, and the energy sources available. Both types of cylinders can provide mains pressure hot water but they do so in different ways

Cost of Installing Unvented Hot Water Cylinders

The cost of installing unvented hot water cylinders can vary depending on their size, the complexity of the installation, and their intended use. On average, installation can cost between £600 to £2000. For more specific pricing, we encourage you to reach out to us for a free desktop estimate.

The Importance of Qualified Installation

A plumbing or gas certification alone does not qualify an individual or company to install unvented hot water cylinders. These units require additional training due to their unique design and operation. Being completely sealed and pressurised, incorrect installation can lead to significant safety risks. Therefore, it’s vital to ensure that only qualified and certified engineers handle the installation of these systems.

Selecting the Right Cylinder Size

Choosing the right cylinder size is key to ensuring efficient performance. Here’s a rough guide:

Experienced engineers and installers can assess your specific needs and make the appropriate recommendations.

Disadvantages of unvented cylinder installation

While unvented cylinders offer several benefits, such as providing high-pressure hot water and eliminating the need for a cold water storage tank, there are also some potential disadvantages to consider. Here are some of the main ones:

Dependency on Mains Water Supply

One of the main disadvantages of unvented cylinders is their dependency on the mains water supply. Since these systems are directly connected to the mains, any disruption to the water supply, such as a mains repair or a local water outage, means you will not have access to hot water until the supply is restored. This can be inconvenient, especially in situations where the water supply is cut off for extended periods.

Higher Installation and Maintenance Costs

Unvented cylinders are typically more expensive to install than traditional vented systems. This is because they operate under high pressure and require additional safety features, such as pressure relief valves and expansion vessels, to prevent over-pressurisation.

Furthermore, unvented cylinders must be installed by a G3 qualified engineer, which can also add to the installation cost. Regular maintenance is also necessary to ensure the system operates safely and efficiently, which can lead to higher ongoing costs compared to a vented system.

Need for Regular Maintenance

Unvented cylinders require regular maintenance to ensure they continue to operate safely and efficiently. This includes checking the pressure relief valve, expansion vessel, and other safety devices, as well as descaling the system if necessary. Failure to maintain an unvented cylinder can lead to problems such as reduced hot water pressure, inconsistent water temperature, or in extreme cases, a dangerous build-up of pressure within the system.

Space Requirements

While unvented cylinders eliminate the need for a cold water storage tank in the loft, they are typically larger than equivalent vented cylinders due to the additional safety features they require. This means you will need sufficient space to accommodate the cylinder which can be a disadvantage in properties where space is at a premium.

Servicing Unvented Cylinders

Regular servicing of an unvented cylinder is essential to ensure its safe and efficient operation. Unvented cylinders operate under high pressure and if not properly maintained, they can pose a risk. Here’s what a typical unvented cylinder service might include:

Safety Checks

One of the most important aspects of servicing an unvented cylinder is checking the safety devices. This includes the pressure relief valve, which prevents the cylinder from becoming over-pressurised, and the expansion vessel, which accommodates the expansion of water as it heats up. These devices should be checked to ensure they are operating correctly.

Inspection of the Cylinder and Pipework

The cylinder and associated pipework should be inspected for any signs of leakage or corrosion. Any issues should be addressed promptly to prevent further damage.

Checking the Thermostat

The thermostat controls the temperature of the water in the cylinder. It should be checked to ensure it is set at the correct temperature and is functioning correctly.

Cleaning and Descaling

Depending on the hardness of your water, limescale can build up inside the cylinder and on the heating element, reducing efficiency and potentially causing damage. The cylinder may need to be cleaned and descaled as part of the service

Checking the Immersion Heater

The immersion heater is a critical component of an unvented cylinder, especially in systems that rely on electricity as the primary or backup source of heating. It’s essentially an electric element that heats the water directly, much like a kettle. Regular checks and maintenance of the immersion heater are essential to ensure the efficient operation of your hot water system

The process of checking an immersion heater in an unvented cylinder involves a series of steps. Initially, a visual inspection is conducted to identify any signs of damage, corrosion, or water leakage. Following this, electrical safety checks are performed which include examining the wiring and connections and testing the electrical resistance of the heater. The thermostat which regulates the water temperature, is also checked for proper functioning and correct settings. Lastly the efficiency of the immersion heater is evaluated. If the heater is not heating the water as expected or if there’s a build up of limescale on the element it may need cleaning or replacement. All these checks ensure the safe and efficient operation of the immersion heater.

Inspecting the Cold Water Combination Valve

The cold water combination valve, which includes a pressure reducing valve, a check valve, and a strainer, should be inspected and cleaned if necessary.

It’s important to note that unvented cylinder servicing should only be carried out by a qualified engineer with the appropriate G3 qualification. This is a legal requirement in the UK due to the potential safety risks associated with unvented systems.

Regular servicing not only ensures the safe operation of your unvented cylinder but can also help to prolong its lifespan and maintain its efficiency, saving you money on your energy bills in the long run.

Final Thoughts

As the search for energy efficient, reliable and cost-effective heating solutions continues, unvented hot water cylinders emerge as an excellent solution especially for larger properties. Their inherent benefits coupled with their compatibility with various energy sources make them a worthwhile investment. Remember, it’s crucial to engage qualified and certified professionals for the installation to guarantee safety and optimal performance.

For further advice, a free estimate, or any other information, please contact us today. We are more than ready to assist you in meeting your heating needs.