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How long can a boiler flue be? Boiler flue regulations

Flue Regulations & Maximum Combi Boiler Flue Length

boiler flue

Every boiler requires a flue to exhaust the heat, steam, or both from the building and to operate a boiler safely, a good flue system is absolutely essential, therefore the entire flue should be well-furnished with the home set up and not too long due to safety and health concerns.

If you plan to purchase a boiler, you must be aware of the flue system and the ideal length for it. There is a clear rule:

“What kind of flue should you choose?” and “how to choose a boiler flue?” are the questions – a Gas Safe engineer will be aware of all legal requirements if you are getting a replacement boiler.

All our boiler quotes include a new flue and fitted to regulations.

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What is boiler flue?

A boiler flue is a device used to transfer heat and hazardous gases from a house’s interior to the outside.

The term “flue” refers to a tube or pipe that is commonly connected to a boiler system at one end and terminates outside of a house.

Classification of gas boiler flue pipes:

Two types of flues are common now. They are:

1.   Horizontal flue

2.   Vertical flue

Horizontal flue:

A boiler flue, most common in the UK, comes outside of a house drilling into an external wall is called a horizontal flue. This flue comes out of a house from the boiler to the outer wall straightly.

Vertical flue:

A flue that exits through the roof or loft is called a vertical flue. To install this flue, the extra money will be needed as it demands maximum length and extra work to be done.

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A combi boiler flue: what is it?

The Combi boiler requires a flue to discharge its steam, carbon dioxide, and carbon monoxide, just like other boilers do. The flue exits the house through the roof or a wall and is connected to the boiler’s main system.

Do you need a boiler flue?

A boiler flue pipe is unavoidably necessary if you own a boiler. Whether your boiler is a system, combi, or condensing mode, the question is irrelevant because a boiler flue is required, as the flue position will be determined by the type, size, and operating system of your boiler.

Regulations for boiler flues:

Steam, carbon dioxide, and carbon monoxide are all byproducts of boilers. These substances are extremely toxic and harmful. Users can sustain fatal health injuries if they misuse the flue system.

To ensure that public health and safety were covered, the government felt the need to create regulations. This rule modifies how a flue should be used.

According to the new regulation, there must be 60 cm between the beginning and end of your boiler’s flue and 2.1 cm between it and the ground.

installing an inspection hatch for your flue will help facilitate regular maintenance and cleaning, ensuring the flue remains free of debris and soot build up for the best efficiency.

What to consider before choosing a flue shape

Flues now frequently have a round or square shape. They vary in size and price as well.

  • Round flue: A round flue is one that is of a particular size. According to the new regulation, a contemporary type of flue uses a 22mm pipe as the round flue.
  • Square flue: An older style of flue, square flues are those that have a square shape. Installation costs are a little higher than for those with a round shape.
  • Home area: Adjust the flue’s output based on the size of your entire home.
  • Placement of boiler and flue in relation to bedroom and window: The boiler and flue should be situated at the appropriate distance from the bedroom and window.

How long can a flue be for a Combi boiler?

Your home’s infrastructure will be key in determining how long the flue should be for your combi boiler, you should make a plan and consult with your boiler engineer to determine the best location for your boiler installation.

Which location will you choose as your target? As well as measure the length of your boiler flue from there? Be careful when selecting the type and shape of your flue because it will represent a long-term investment in your family.

Why is it important to understand boiler flues?

Installing a new boiler will be an investment in the future of your family, as it will cost you significantly, before installing a boiler, your main concerns will be your family’s safety and energy efficiency.

One of a boiler’s most important components is the flue, so it’s important to comprehend how to install one as well as the associated costs and maintenance requirements, as your needs will determine which boiler and flue are best, according to heating engineers.

Cost of Combi boiler flue


In accordance with your flue’s installation components, including its length, shape, and exterior (vertical or horizontal),

Due to energy costs, the average cost of a best combi boiler flue will range from £100 to £200.

When replacing an old boiler, the cost of a new combi boiler should include a boiler flue.

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