Category - Boilers
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Will Scholfield, Engineer

31 Jan : Updated 18 Apr ● 6 min read

A guide to hot water cylinders

Throughout the UK, many homes rely on a hot water storage tank to supply heated water to their properties. Unless you want cold showers, it’s an essential component of warming up your home. 

Unfortunately, selecting the appropriate cylinder for your home can be a tricky task with a wide range on offer. We know that not everyone pays attention to how water is heated in their home. However, understanding what’s right for your property could make all the difference. So, if you’re unaware of the different types of hot water cylinders available - we’re here to help. Investing in the right one could save you money and energy.

How does a hot water cylinder work?

Hot water cylinders are crucial to many modern homes. Without them, we would be without hot water. To put it simply, hot water cylinders are tanks used in domestic and commercial buildings to provide a steady stream of hot water throughout the property. When needed, the tank will pass this hot water throughout your house into taps and showers.

What are the type of hot water cylinder?

Much like boilers, there are a range of different types of hot water cylinders. Which one you’ll need will depend on your boiler type, along with your hot water requirements. When it comes to storing and distributing hot water in your home, there are a number of options you can use. Hot water systems in the UK generally fall into two types: vented and unvented. 

The main difference between vented and unvented? Is the way each cylinder is supplied with water. In both systems the cold water is fed into the base of the water cylinder. It then rises to the top when heated and then is piped to the house to be used. Finally, the base is replaced with cold water.

So, let’s find out more.

What is an unvented cylinder?

An unvented cylinder system operates purely from mains water and is a pressurised system that results in powerful water flow. This is because unvented cylinders are connected directly to the mains system - negating the need for a cold water tank. Unvented cylinders work with existing pipework, making them a simple system to fit. Because water is taken straight from the mains, tanks can be located anywhere within a property. 

What is a vented cylinder?

A vented hot water cylinder is a system that relies heavily on gravity to ensure hot water and heating can be accessed throughout a property. In a vented system, water is fed from a cold water tank usually kept in the loft, and then passed through a vent pipe to a hot water cylinder situated within the house. This venting allows the water to expand in the cylinder and ensures that the excess water is condensed safely into the cold tank.

As a standard vented system relies on gravity to supply hot water to your property, the hot water cylinder has to be located directly below the cold water storage tank. This is to generate the required water pressure to flow throughout the house.

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How do you choose the best hot water cylinder?

When deciding between a vented cylinder and an unvented cylinder, there are a few things to consider:

Vented cylinders are usually simpler, cheaper to install and preserve. An unvented cylinder requires no water tank, therefore taking up less space. This offers you more flexibility on where it can be installed. Similarly, unvented cylinders tend to provide stronger water pressure.

Although, with a vented cylinder, if the mains water supply is cut off - you’ll still be able to heat your home and have access to hot water.

It’s also important to consider what heating system you currently have in your property, along with how strong your mains water pressure is. For example, if you have an old system that has never been upgraded, your pipes and radiators may not be able to handle the high water pressure that comes with an unvented cylinder. On the other hand, there’s no point installing an unvented cylinder if your water pressure is low - you may have to install an extra pump to boost the water flow.

What size hot water cylinder will you need?

Fitting the right size hot water cylinder is crucial. It needs to be large enough to handle the demands of hot water usage in your home - but small enough so that you’re not wasting energy heating and storing more water than you need. 

Some people may worry that having a hot water storage cylinder means that you’ll run out of water whilst having to wait for it to fill up again, but if you select the right size for your property - this shouldn’t happen. Both vented and unvented hot water cylinders are available in a wide range of sizes. These can vary anywhere between 74 litres (16 gallons) to 450 litres (99 gallons).

Unfortunately there is no ‘one-size-fits-all’. So when deciding what size hot water cylinder you’ll need there is a general rule you can follow… allow around 35-45 litres for every household occupant. 

On average, a standard domestic household with 4 occupants will use around 200 litres of water a day. However, it should be noted that hot water cylinder sizes will differ depending on the household and your own usage.

Insulating your hot water cylinder

Insulating your hot water cylinder is one of the easiest ways to save both energy and money. Along with speeding up the heating process, it maintains the desired operating temperature. By insulating the tank, you can greatly reduce the amount of heat that escapes - making it more efficient, and cheaper to use. This because you’re not having to constantly re-heat water for household use.

It’s relatively simple and cost-effective to insulate a hot water cylinder. This can easily be done at home, consider insulating with cylinder jackets. These fit over the tanks and the foam tubing that covers exposed pipes between the cylinder and the boiler. This is a straightforward way to cut costs, reduce heat loss, and keep your water hotter for longer.  

It’s important to select the right hot water cylinder and boiler for your home, for optimum usage. We can offer advice on your complete heating system - including hot water cylinders. If you have any questions or need help in finding the right boiler for you, use our live chat for an instant conversation with one of our engineers.

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