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Unvented Cylinder Installation: A Guide

You might be looking forward to replacing your vented cylinder with an unvented cylinder. And we can see this is why you are here!

You don’t worry your head about it since this article is a comprehensive guide for you with everything you need to know. We will be putting forward the advantages and disadvantages along with a monetary guide for you. Let’s get into it.

Vented and Unvented Cylinder – The Difference

What sets the vented and unvented cylinder apart is that the vented cylinder gets its water supply from the large water tank from the attic via vent pipe. Contrarily, the unvented one takes its water supply directly from the mains.

In terms of water pressure, it depends on gravity. There is no need to vent the system in the vented hot water cylinder. Once the tap is turned on, you instantly get a hot water supply. The drawback is that the large water supply tank occupies a lot of space.

On the flip side, an unvented hot water cylinder can solve this problem since it does not involve a water tank and saves that space. Moreover, it delivers better pressure with a good water flow because it is connected directly with the mains. We hope you have got the differences by now.

Should You Go for Unvented Cylinder Installation?

People have started considering removing vented water cylinders given the unreliable water pressure and the amount of space they occupy. But here is a significant bit. An unvented water cylinder may not be a good fit for your home if you reside in an old property with traditional pipework. This is because such systems are not built to take high water pressure.

Nevertheless, you might find yourself relatable to either of the following scenarios;

If you reside in a home with one bathroom and less than 10 radiators, you can consider getting rid of your vented cylinder. A combi boiler would be an ideal alternative for you. A combi boiler is a single compact unit that acts as a water heater and a central heating boiler as well.

Another case can be if you live in a comparatively larger home with more than 1 bathroom and more than 10 radiators. The viable option for you will be the installation of an unvented cylinder system.


Unvented Cylinder Installation – Advantages

  • Free up Some Space: Since an unvented cylinder is connected directly with the mains, installing it means you are saving up some space in your home.
  • Stronger Flow of Water: Taking water directly from the mains, an unvented cylinder delivers a reliable flow of water.
  • No Risk of Freezing: If you install an unvented cylinder, you don’t have to worry about the pipes and tank getting frozen in winters because the tank would no longer be in the attic.
  • High Volume of Hot Water: An unvented cylinder will deliver a high volume of hot water, enough to run several taps and showers simultaneously.
  • Reduce your Heating Bills and Carbon Footprint: Unvented cylinders are capable of being operated with solar thermal panels, so you can make good use of them, reducing your heating bills.
  • Ease of Place: Unlike a vented cylinder, which requires installing under the cold water tank, an unvented cylinder doesn’t require any specific place for installation.
  • Quieter than Vented Cylinders: You will not get to listen to the gurgling of water since the tank is refilled smoothly.
  • No Risk of Contamination: There is no risk of contamination as the unvented water cylinders are sealed.

Unvented Cylinder Installation – Disadvantages

  • Dependent on Mains: The supply of hot water depends on the mains. If the mains get turned off, there would be no hot water for you.
  • A Bit Costly: Unvented cylinder systems are more expensive than the vented ones due to the costs involved for additional safety systems. Also, they can operate under extreme pressures.
  • Need a Qualified Installer: You need a qualified installer and regular maintenance for unvented cylinders.

Working of an Unvented Cylinder

As we have discussed earlier that an unvented cylinder is directly connected with mains, which implies that the water stored in its tank is constantly under pressure.


An unvented cylinder can undergo either direct or indirect heating.

  • Direct Heat: An electric immersion heater, as the name suggests, is immersed inside the vessel. It heats the cylinder contributing to direct heat.
  • Indirect Heat: If the cylinder is heated from an external source, the heat is indirect. External sources may include a boiler, heat pump or solar thermal panels.

Usually, an unvented hot water cylinder works on indirect heat, also including an electric immersion heater as a backup.


Once you turn on the tap or an appliance, the outlet pipe takes the hot water where it is required. To ensure that the pressure remains constant, the hot water distributed by the outlet pipe is replaced by cold water from the mains. The pressure is constantly maintained no matter how many outlets are provided with hot water.


The safety systems installed in unvented hot water cylinders ensure that the pressure and temperature remain checked to not cause any mishap.


The material used for unvented cylinders is stainless steel or heavy gauge copper, the extra layers of which can induce insulation.

Qualified Installers Needed for Unvented Cylinder Installation

As per G3 Building Regulations from the government, a qualified engineer must install any vessel containing hot water ranging more than 15 litres. The regulations demand a qualified engineer with G3 certification who also has had CITB training to proceed with the installation. Given the fact that unvented hot water cylinders involve high pressure and large volume, the need for a qualified installer is totally justified.

Now that you have decided to get an unvented cylinder installed in your home, there is an important thing to do prior to the installation. Contact and tell your local Building Control Department about your plan of installation. This is for safety purposes so that unsafe water pressure or temperature does not cause an explosion in future. The process may require installing pipework and valves in your property for relieving pressure which would protrude out of the building.

Likely Cost for Unvented Cylinder Installation

An unvented cylinder cost somewhere between £300-£1,500, though it can exceed £2,000 in some cases. Following are the factors the cost of an unvented cylinder depends upon;

  • Brand
  • Model
  • Capacity (litres)

Cylinder with higher capacity costs more than ones that can hold lesser volume.

For your convenience, we have compiled average pricing corresponding to the leading brands for unvented hot water cylinders (excluding installation price). However, the accurate price can only be known depending upon the supplier you choose.

Brand Capacity (l) Average Price
Worcester Bosch 90 – 300L £600 – £1,000
Gledhill 90 – 400L £300 – £1,200
Heatrae Sadia 70 – 500L £500 – £2,300
Telford 90 – 400L £300 – £1,200


Cost of installation

The cost varies largely depending upon whether you just want to upgrade your old unvented cylinder or install a whole system.

  • Upgrading: Upgrading an old unvented cylinder can cost you somewhere between £250 to £450.
  • Replacing: If you are looking forward to replacing an entire heating system, the cost will exceed £1,500.

Why does an unvented cylinder installation cost more than vented cylinder installation?

Usually, an unvented cylinder installation is costlier than a vented cylinder installation. The reasons being;

  • Complex process
  • A higher level of risk
  • A higher level of training

If you have made up your mind to get an unvented cylinder installation, here is a tip for you. Get the quotes from multiple installers and compare them. Then go for whoever is viable for you.

Maintenance and servicing

According to BS2870 Health and Safety Regulations, it is imperative for homeowners to get professional service annually. The intent is to ensure the efficiency of the system and the detection of any minor fault it may have. The service would help avoid possible danger or a big problem in the boiler and cylinder.

The cost for the yearly professional service would range from £50 to £100. The price includes both for the boiler and the cylinder.

Get multiple quotes for your unvented cylinder installation

You might be wishing to install an unvented hot water cylinder in place of your traditional vented cylinder or replace your old unvented cylinder with a new one. In either case, getting multiple quotes and making a comparison is always a better idea. This way you would feel confident that you are getting the best service at the right price.