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Vented or unvented heating system

Changing from a Vented to Unvented Heating System


Since the rise of combi and system boilers, the vast majority of homes have been fitted with an unvented heating system. Properties built in the 1960s and 1970s are likely to have a vented heating system that includes a regular boiler.

With unvented heating systems being the system of choice nowadays, should you consider changing from a vented to unvented heating system? Explore the pros and cons to both heating systems and find out what’s involved in replacing a heating system.

Vented and Unvented heating systems: What’s the difference?

Vented heating systems include a feed and expansion tank at the highest point – typically in the loft. From this tank, cold water is fed down to the boiler and cylinder where it is heated. The process of heating water causes it to expand and excess water is stored in the tank so that there isn’t too much water in the heating system.

The only type of boiler that can be installed as part of a vented heating system is a regular boiler. Otherwise known as a conventional or heat-only boiler.

Unvented, or sealed, heating systems have no need for a tank in the loft. Instead, they take water directly from the mains. To deal with water expansion, the system has an expansion vessel.

Sealed heating systems make it possible for a combi or system boiler to be installed. Combi boilers are all-in-one heating systems which deliver heating and hot water on demand. Whereas a system boiler must be installed alongside a hot water cylinder.

Why remove a vented heating system

Vented heating systems are often found in older properties and were the heating system of choice until combi and system boilers came along. Modern properties are more likely to have unvented heating systems and removing your vented system is worth considering because of the following:

  • Heat can escape through the tanks in the loft which will decrease the efficiency of the system – leading to higher heating bills
  • You’re restricted to heat-only boilers (combi and system boilers can’t be installed as part of a vented heating system)
  • The cold water storage tank in the loft can be prone to freezing and contamination
  • Debris can make its way into the heating system via the tank and cause blockages within the heating system

Benefits of unvented heating systems

Changing from a vented to unvented heating system offers the following advantages:

  • Take up less space as there’s no need for a water tank in the loft
  • More flexibility in terms of where the cylinder can be installed as it’s being fed water from the mains rather than a tank
  • Able to deliver water to taps, baths and showers at a higher pressure (this will depend on the mains water pressure)
  • Makes it possible to have a combi or system boiler installed

How much does an unvented heating system cost?

Switching from a vented to an unvented heating system means having a new boiler and cylinder installed. The costs of each will vary depending on the manufacturer and model so it’s worth doing your research.

Unvented Heating System Parts
Potential Cost (before installation)
Combi Boiler
£500 – £2,000
System Boiler
£500 – £2,500
Unvented Hot Water Cylinder
£300 – £2,250

Note: You will only need either a combi or system boiler as part of an unvented heating system and combi boilers do not require a cylinder.

If you’re replacing a vented heating system with an unvented system then the installation costs will be higher than if you were to have a like-for-like replacement. By like-for-like, we mean continuing with the same type of heating system but having it upgraded.

This is because the pipework will need to be rerouted and the tank in the loft removed. In addition the cylinder and boiler will need to be replaced too. You may also need new radiators if the current ones are unlikely to be able to withstand the increased pressure.

To get the most competitive price when having a new heating system installed, we highly recommend comparing quotes. By sourcing quotes from multiple installers you’ll know whether you’re getting a competitive price.

Using Boiler Guide, you can get free quotes from as many as 3 heating engineers in your local area. Each will be in touch to provide a free no-obligation quote for you to then compare.

Are there any downsides to unvented heating systems?

Having an unvented heating system installed comes at a higher price than vented heating systems. Particularly if it’s a vented heating system that’s being replaced. Additionally, they’re made up of fewer parts which can reduce maintenance costs.

In the event that the mains water supply is switched or cut off then your property will be without hot water. Vented heating cylinders on the other hand are fed water from a storage tank in the loft.

It’s also important to check that the new unvented heating system is compatible with modern power showers and mixer showers, if you have them.

Should I stick with a vented heating system?

Depending on the circumstances, sticking with a vented heating system may be the best option. For the time being, at least. These include:

  • Your regular (heat-only) boiler only being recently installed and is still able to comfortably heat your home in a reliable and efficient manner
  • The pipes or radiators in your property wouldn’t be able to handle the increased water pressure

Additionally, changing your heating system from vented to unvented would be more costly than a like-for-like replacement. So, if you’re on a budget then a new vented heating system could be the better option.

If you’re considering replacing a regular boiler with a combi, find out if it’s a good idea in Should You Change a Conventional Boiler with a Combi?

Get quotes from local heating engineers

Whether you’re looking to change from a vented to unvented heating system or want to upgrade your vented heating system, Boiler Guide can help. Simply complete one of their online and you’ll be connected with up to 3 heating engineers in your local area. Each will be in touch with you to provide a free quote for you to compare. You’ll then be in a position to go ahead with the work knowing that you’re not paying over the odds.

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