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Can I Install Boiler Flue Through the Roof?


Yes, you can install a boiler flue through the roof. Nonetheless, there are regulations you have to follow to do it correctly. Continue reading to find out more about boiler flues and how you can install yours successfully.

What’s a boiler flue?

Flues are to boilers what exhaust pipes are to cars. In case you didn’t notice, most boilers burn fossil fuel to produce heat. Specifically, we’re referring to gas, oil, and LPG boilers.

Besides heat, boilers also produce harmful gases as waste products. Of them all, you need to be wary of carbon monoxide. It’s a colourless, odourless, and very poisonous gas.

Your boiler flue is responsible for re-directing these gases away from your boiler and out of your house.

All modern boilers have flues (combi, system, and regular boilers). Back boilers are the only ones that don’t require them. Nonetheless, they’re rare nowadays. Most people prefer modern boilers since they’re more efficient and easier to maintain.

What are the differences between horizontal and vertical boiler flues?

Indeed, despite their differences, they all serve the same purpose. The decision to install one over the other is usually dictated by specific circumstances that we’ll explain later.

Horizontal boiler flues

Horizontal boiler flues are the most popular in the UK. Most of the time, they’re round in shape and come in black or white. Yours probably extends backwards from your boiler and pops through the wall.

Generally, if your boiler is less than 15 years old, it probably has a horizontal flue. To confirm, all you have to do is peep at the opposite wall where your boiler is installed. If you see a pipe, then yours is a horizontal flue.

Vertical boiler flues

Indeed, horizontal flues are easier to install. However, there are times when they’re not ideal. For example, if the boiler is to be installed in one of the property’s inner walls. In such an event, the technician will have the flue leave the house through the roof.

Vertical flues are more difficult to identify and are usually mistaken for chimneys. This is because most owners prefer to have them encased for aesthetic purposes. No one wants to have a weird-looking pipe protruding at the top of the house.

Are vertical flues more expensive?

Indeed, vertical flues will require more expertise during installation. Therefore, they slightly cost more than horizontal ones. In addition to that, you’ll also need more parts and time.

Most boiler installations usually require one fully-qualified engineer. However, since vertical flues involve roofs, you might have to hire a roofing contractor. The most crucial thing is to ensure the seals are done correctly to prevent leaks.

Note: If you’re installing a new boiler, you’ll seldom have to worry about the costs. The one-time boiler installation package will cover the flue installation costs. On the other hand, if you’re replacing an existing pipe, expect to pay around 100 pounds.

Boiler flue roof regulations

In case you didn’t know, boiler flue regulations are part and parcel of building regulations. Therefore, they are necessary conventions that must be followed. Failure to adhere to them will not only cause health problems but might also draw penalties. Carbon monoxide is hazardous.

We’re not going to mention all of them. Below are some of the most important ones.

Away from windows and doors

Generally, you should never install boiler flues close to any openings. In this case, we’re referring to doors and windows. The idea is to prevent the harmful gases from re-entering your property.

Of course, the actual dimensions will depend on your house’s size and arrangement. However, the regulations state that flues should be at least 600mm away from doors and windows.

A height of 2.1 meters

This regulation applies to flues that face public spaces like streets. It’s not only about your safety but also that of others. Ideally, it should be at an overhead height (2.1 meters from ground level is the minimum height required).


Your boiler’s main task is to produce heat. It achieves this by burning fossil fuels. Therefore, the waste gases produced are also hot. Therefore, the flue shouldn’t make contact with any material that can be damaged by heat (For example, plastic guttering).

Of course, we expect you to call your trusted heating engineers and allow them to install the flue for you. Below are some of the steps that must be followed to meet boiler flue regulations:

  • To prevent leaks, the duct must be tightly secured with caulk and sand cement on both sides.
  • The engineer should ensure the flue length is accurate to prevent dripping. Additionally, if the measurements are wayward, it might mess with the boiler’s performance. Too many extensions will reduce the system’s efficiency.
  • All pipework and extensions must be secured with bolts and screws.
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