vented hot water cylindersBefore 1989, it was much easier to decide which hot water cylinders to install. This was largely because only vented cylinders (pdf file) were legally allowed for domestic use. But since then, unvented cylinders have been introduced and people now have the choice of vented and unvented hot water cylinders. Each has their benefits and drawbacks to consider.

The hot water cylinder you choose also depends on whether your mains water is fed directly or indirectly into the system. This also determines how water is heated, either through a heat exchanger or electric immersion. You will find that many homes take advantage of both methods by installing a combination of both, one for daily consumption and another for backup or storage.

Vented Hot Water Cylinders

Even after the introduction of unvented water cylinders, vented systems are still more commonly used. In this system, the mains water is stored in a cold water storage tank. Since the water supply uses gravity to distribute water around the house, this tank is usually located in the loft. Water is fed indirectly and a heat exchanger is needed to produce hot water.

Benefits of vented hot water systems

Vented hot water systems are much less complicated to install. For this reason, they are more affordable and easier to maintain. With this system, water is heated when it passes a series of coils – the heat exchanger – which is located within the unit. This makes vented hot water cylinders very economical to have.

The fact that the mains water is fed into a storage tank makes it handy when the water mains is cut off. You will still have some backup hot water supply, despite not having water running through the mains.

Drawbacks of vented hot water systems

On the other hand, the use of a tank means a fair amount of space is required to install a vented hot water system. And, with the heat exchanger producing all the hot water, you risk being left with no hot water should the part breakdown.

Another drawback with using a cold water storage tank is low water pressure. Because the water pressure is driven by gravity, pressure can drop when more than one tap is being used at the same time. To resolve this, a pump needs to be added to guarantee good flow of water around the house at all times.

Hot water cylinder installation cost

The installation cost of vented hot water cylinders depends on the complexity of the project and also on the location that you are based in the UK. However, there are ways to reduce the installation cost when it comes to replacement cylinders.

Plumbers usually quote a day’s rate for this kind of project when the job is not very complicated and the cylinder can be removed easily. Installing a standard vented hot water cylinder would cost between £500-£600, if you leave the plumber handle everything. The price includes the water tank (£200), the thermostat (£20), the labour (£250-£350), the cost of scrapping the tank and any waste created plus any secondary materials such as washers, fitting and PTFE tape.

You can also reduce the installation cost by:

  • Making all the connections as easy as possible to access by positioning them all on one face.
  • When replacing an old cylinder, ensure that the connections are in the exact same position as in the new one.

Unvented Hot Water Cylinders

The newer unvented hot water systems have the mains water directly fed into them. There is no need for a cold water storage tank. Hot water is basically produced similarly to vented systems but instead of a heat exchanger, it uses an immersion heater which runs on electricity. Unvented hot water systems constantly provide hot water at mains pressure.

Benefits of unvented hot water cylinders

Those who have unvented hot water cylinders installed in their homes can always rely on the pressure from the mains. This means that the system can unvented-hot-water-cylinderbe installed almost anywhere you like, without having to depend on gravity for good water flow. You won’t have to worry about pressure getting a little too high either as many have in-built safety devices to cope with this, as well as the issue of water expansion. As with the immersion element, this makes unvented systems more reliable and even if it does breakdown, they are easy to find and replace.

Disadvantages of using unvented hot water cylinders

As you may have guessed, unvented hot water systems are more complex than vented cylinders. Installing one will require a specialist and this means added cost. There is also an issue with unvented systems not being compatible with some power showers and mixers. The use of an electric immersion heater also increases its running costs. Electricity is three times pricier than gas, which is what most vented systems run on.

Other than vented and unvented hot water cylinder systems, there are other boilers that can supply you with hot water without the need for cylinders. If you choose to install hot water cylinders, keep in mind that most are made from thin copper. When not insulated properly, your thin copper cylinders can suffer from a lot of heat loss. A good coat of foamed polyurethane will ensure that your cylinder system is always running at its most efficient.

Costs for replacing an unvented hot water cylinder

If you would like to upgrade your hot water cylinder from vented to a system the cost should be around £700 in total for both labour and the cylinder as this job usually takes usually two days for a plumber to install a stainless steel, unvented, insulated and pressurised hot water cylinder. However, prices can vary depending on where you live in the UK.

Gas Gafety Guidelines (PDF)


Watch the following video for more useful advice

What type of cylinder is best for me?

There are some important factors you should consider while making a choice between vented and unvented cylinders. These include:

  • The size of your house;
  • The type of heating system and the amount of pressure from the mains supply; and
  • The cost of installation and routine maintenance.

What Existing Heating System and Mains Pressure are you working with?

Vented hot water cylinders and regular heating systems are the traditional systems that are most common in older homes. It is important to choose the right cylinder type to avoid any compatibility issues. If an unvented water cylinder is installed on a regular heating system, it may cause an increased pressure far above what the old network pipes and radiators can handle.

On the other hand, if the pressure from the mains is relatively low, installing an unvented system will not lead to any complications. However, it is important to assess all the possible options because an unvented water cylinder will maintain the current low pressure while supplying water directly from the mains. A possible work around would be to install an additional pump that will amplify the pressure of the flow.

How big is your House?

You should not consider installing a vented cylinder if you do not have plenty of space preferable with high elevation. A vented water cylinder system needs to be placed in an elevated position to store the cold water because the system uses gravity-enhanced delivery.

Do you have two or more bathrooms?

If yes, then a vented cylinder is the best option for your home because the cold-water tank supplies sufficient water concurrently without dropping the water pressure.

On the other hand, an unvented tank relies heavily on the flow from the mains. If the mains are divided into several outlets, which are used simultaneously, the pressure will become weaker. However, this will not be an issue for any home that has less than three bathrooms.

What Size of Hot Water Cylinder Do I Need?

Choosing the right size of cylinder is a very important factor as it will ensure that it can meet the water needs of your home without causing severe shortage or energy-wasting by heating more than the required amount of water.

The capacity of a cylinder is calculated in liters, however many homeowners do not have an idea about the quantity of water they use per day. To calculate the right capacity, you need to look beyond taking a bath, washing dishes and watering the lawn. Proactively think about the morning rush periods when everyone will be in the bathroom and the busy weekends when you are watering the lawn while operating the dishwasher and washing simultaneously.

However, the easiest way to estimate the required size is to make an estimation based on the number of bedrooms, bathrooms, and showers. The required capacity does vary slightly depending on the water-heating method (i.e. direct or indirect heating system) because the cylinders that are heated indirectly through boilers usually reheat quicker.

FREQUENTLY ASKED QUESTIONS

Typical Problems with an Unvented Hot Water Cylinder and Practical solutions

Are unvented hot water cylinders dangerous to work on?

Why I am not getting hot water from my unvented hot water cylinder?

Why am I not getting water at all since I have an unvented hot water cylinder?

What about when my water is too hot on my unvented cylinder, why is this?

What about when my water is too hot on my unvented cylinder, why is this?

What about when there is water dripping from the plastic pipe, is there a problem with that?

There is water pouring through the pipe of my unvented hot water cylinder, what should I do?

Do I have to get my unvented cylinder serviced every 12-months?

What does the expansion vessel do on the unvented hot water cylinder?

I’m not getting enough water through from my tap and I have an unvented cylinder, why?

What is the Tundish for on the cylinder?

Who do I call if I have a problem with my unvented hot water cylinder?

What should I do if my unvented boiler isn’t being used?

If I have poor water pressure, can I have an unvented cylinder?

Which is the better cylinder, a vented or an unvented hot water cylinder?

Why do we have so many pipes on an unvented cylinder?

What should the pressure be on the unvented cylinder?

Why do we have so many pipes on an unvented cylinder?
What should the pressure be on the unvented cylinder?
How do I go about becoming a professional unvented boiler fitter?
Why is my unvented cylinder leaking?
Why has my unvented cylinder exploded?
What should be the temperature on the immersion heater of my unvented hot water cylinder?
Does an unvented cylinder heat up via direct cylinder or does it need a system boiler to heat up?
How would I know if your plumber is a qualified unvented hot water cylinders plumber?

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