BlogHow Much Does It Cost to Replace a Boiler Flue

January 23, 2022by plumber


The replacement of a boiler that is older particularly one that was installed before 2005, could require changing the boiler’s flue. This is a crucial task that must be handled by a Gas Safe registered installer. In many cases, it can be a skilled, but simple task that is typically included in the cost of installing the boiler. There are however several boiler flue regulations that need to be considered, and may at times make changing the boiler’s flue more difficult.

How Much Does It Cost to Replace a Boiler Flue?

What Does a Boiler Flue Do?

In a modern fan-assisted condensing boiler, the flue can as well describe itself as a gas/air duct since it is made up of two channels for gas and serves two purposes:

  • The purpose of this is to expel the exhaust gases of the boiler to the outside air which is where they disperse into the atmosphere.
  • Injecting fresh oxygen (oxygen) in from the outside of the house to the boiler to heat natural gas.
  • A common gas boiler flue (or pipe too many) is 100mm. It has two ways for gases to pass through. The central pipe of 60mm is used to bring the exhaust gases out, while the outer ring of 100mm is used to draw in the fresh air.

Boiler Flue Terminal

The point at which the flue’s end is known as the terminal. It is where exhaust gases are released into the air (as shown in the photo above). Boiler flues with 125mm diameter can also be used for pipe runs that are longer.

Why Would I Need to Move My Boiler Flue?

The rules and guidelines for the placement of boiler flues have significantly changed since condensing boilers became obligatory in 2005. The tightening of regulations was done to enhance safety and minimize nuisance to neighbours, occupants and passers-by who are exposed to the exhaust gases from boilers that condense. It means that the terminal for the flue which is where gasses are released is not so close to construction elements such as doors, windows roof eaves, windows, and other components, including parking spaces.

Another important modification is that there is now guidance for the inspection of flues hidden from view so that all lengths can be properly examined for commissioning and for annual maintenance. This may disrupt if the flue is incorporated in the fabric of the structure and could be particularly problematic in flats in which a shared flue system can be put in place.

Even if the boiler’s flue location is adequate the layout of flues has evolved in the past and flue terminals are generally being circular, whereas older models that were not condensing are rectangular.

If you replace an old flue, a house may leave an oddly shaped gap in the brickwork that requires to be repaired. It could be replacing 3-4 bricks or the in the worst case, 6-8 bricks. If the flue is located on to the ceiling (a horizontal flue) instead of the wall (horizontal flue) other modifications might be required.

What Does Installation of a Boiler Flue Cost?

For a simple horizontal installation of a flue, it is around £200 for the parts and labour which includes VAT. The most basic flue kits that are used on the most popular boilers are priced in the range of £100 and the remainder of the expense is labour to cut through the brickwork and create.

This is a must in an installation price to replace a boiler; when the boiler’s position is changing, then the process of replacing the old flue could be charged separately. Finding the exact match bricks isn’t easy, however, an installer in the area will typically already know how to find the bricks.For more difficult and complex installation, the price could rise significantly and be as high as the range of £500-£600.

This could include the construction of six or seven meters of flue pipe around several bends and through a roof and then repairing the brickwork after the old rectangular flue was removed. If you are working at a height, an access tower is needed that can be priced between £50 and £100 per week.

Where’s the Best Place for A Boiler Flue?

It is contingent on the structure of the house, but the most straightforward installation is one that is mounted on a wall and has horizontal flues that run straight through a nearby wall, either towards the rear or either side. There are various rules and regulations about boiler flues.

The majority of them can be designed to make sure that exhaust fumes are evenly dissipated to the outside without causing dangers to the occupants or people walking by the property.There are additional aspects that must be taken into consideration and your Gas Safe registered installer can help you during an on-site survey.

·         Horizontal Boiler Flue Layout

In the above diagrams, the horizontal flue is positioned through the inside and out brickwork of the outside wall. While the thickness of outside walls differs, mist manufacturers provide the option of a telescopic flue that can handle reasonable changes in wall thickness. When the flue is put in place, it is bent to the back (a couple of degrees) to let any condensation of moisture inside the pipe move back to the boiler.

·         Vertical Boiler Flue Layout

Is not every house that has an exterior wall that is suitable for the installation of a flue terminal? In this situation, it is possible that a vertical flue will be required, and is likely to be installed into the roofing of the house.

·         Gas Boiler Flue: Vertical Flue for Flat Roof

Boiler manufacturers provide a selection of flue bends that can be combined to make various shapes of flues. They also have specialized parts that can be used to overcome specific challenges, for example, the ridge tile that has a pre-molded opening for the flue.

·         Terminal for Vertical Boiler Flue

Flues for vertical heating are an increasingly popular option for homes with single-story bungalows.

When Should a Terminal Guard Be Used in conjunction with A Boiler Fire?

The ideal flue terminal should be placed so that it is not able to touch people (i.e. over the threshold of 2.1m) however this isn’t always feasible. A flue terminal guard is employed to stop anyone from getting burned if they contact the hot terminal.

This guard is a smooth mesh that has no sharp edges and provides an adequate 50mm distance from the terminal of the flue. A flue terminal guard can be utilized for flue terminals that are less than 2 meters above the surface in an area where pedestrians can walk, or when the flue runs through an unsupported roof, that people can access. The design and construction of a flue terminal would cost about £20-40.

Do You Need Planning Permission for A Boiler Flue?

In general, you won’t require planning permission for the flue of a boiler, but there are some situations where planning permission may be necessary:

  • Find out from your local authority for planning whether approval is required.
  • In conservation zones, World Heritage sites, national parks, and other areas of exceptional natural beauty, the flue must not be placed on the main or side elevations if it is visible through the roadway.
  • The flue is situated at the back of the building and extends over a meter higher than the highest point on the roof.
  • It’s your Gas Safe installer who should be in a position to help you with this.

What About Shared Flues

Common flue systems come with particular requirements that an expert installer will be able to assist you with. A boiler connected to the communal system will typically require a flue gas non-return flap or valve to ensure that exhaust gases do not be re-introduced into the boiler.


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