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What is the Difference Between Horizontal & Vertical Boiler Flues?

We can differentiate horizontal and vertical flues from each other based on their arrangement. Nevertheless, both the flues function similarly. If you install a horizontal flue on your property, it will show protruding out of the wall. Alternatively, a vertical flue would be visible on the roof of the building. Though horizontal flues are more common across the UK, some structures demand vertical flues.

Regardless of their positioning, both the boiler flues are quite identical when it comes to the operation they perform. Their function is to let out the harmful fumes emitted from the boiler. This way, they prevent these waste gases from leaking into the living area.

Even though both boilers flues carry out a similar job, a better understanding of the two would assist you a lot in your boiler replacement.

All About a Boiler Flue!

Any heating system of today, that involves burning fossil fuels, would generate toxic fumes as a by-product. If these gases somehow make their way into the living area, the chances are that the ones living there can inhale the gases, unintentionally, which can prove fatal afterwards. How to protect ourselves from these gases? Well, the boiler flue pipe does this job for us by discharging such gases.

How can we differentiate between a Horizontal and a Vertical Flue?

We have already gotten the purpose behind a boiler flue, that is, to discharge harmful gases produced as a by-product. However, it is imperative to recognise which one you have to install. And it is not even difficult; here is how you can do it.

Identifying a Horizontal Flue

If you see the flue jutting out of the wall, it must be a horizontal one. Horizontal flues are generally used more often across the United Kingdom. Their colour varies from coal-black to chalky, and the shape is mostly round.

Identifying a Vertical Flue

As we have already discussed, horizontal flues are more common; there are some cases when you need a vertical flue. For example, if a house is structured where you need to install the boiler under the room and not the wall, a vertical flue would do better. This way, it gives the impression of a chimney, protruding through the roof, making its way to the top.

While doing so, you have to make sure that you have gotten the roof sealed properly. You can get it checked by a roofing contractor after the installation of the flue.

Want to know whether you have a Flue in your Home?

At this point, you would be eager to know whether you have a flue installed in your home or not, so here you go. We have talked before that any heating system today running on fossil fuels must emit harmful waste gases. And these gases need to be regulated every time they are emitted. The chances are that you have already had a flue installed in your home.

Look for the horizontal flue from outside of the wall; if it has a horizontal black or white thing extending out of it, it is most probably the flue. Similarly, a vertical flue can be seen sticking out from the roof. One common thing to notice is steam. If the boiler is in action, fumes would be coming out of the flue pipes. These are the same gases that would otherwise be roaming in your home if the flue had not prevented it.

Is a Flue Pipe a Necessary Requirement for a Boiler?

Usually, a flue pipe goes hand in hand with the boiler; however, exceptions do exist. If your heating system is operated by a back boiler, an electric boiler or any other heating system that runs on renewable energy, the flue won’t be a necessity. Here is the logic behind it:

  • Back boilers are intentionally installed in the chimneys that let the waste gases and steam to escape without the need of a flue. These boilers were a hit in the 1960s but now not so much as they are larger units and don’t provide the same efficiency level as their modern counterparts.
  • On the other hand, electric boilers run on electricity to perform their function, ruling out the need for exhaust gas disposal.

While boilers running on fossil fuels would be burning oil or gas as their primary fuel. Burning fossil fuels produces waste gases as a by-product; these gases if released into the living area, could have dire consequences for the occupants. Thus, making the need for having a flue pipe installed along with these boilers an absolute necessity.

Effects of Waste Gases on Human Health

All of the gases produced as a by-product by the boilers could prove extremely harmful to human health. But the most dangerous among all of them is carbon monoxide (CO). This has been termed as the “Silent Killer” as it is a colourless, odourless and tasteless gas and can’t be detected without a carbon monoxide alarm. If inhaled for long durations of time, it could prove life-threatening. Some of the common carbon monoxide poisoning symptoms include:

  • Nausea
  • Dizziness
  • Headache
  • Vomiting
  • Shortness of breath
  • Chest pain
  • Confusion
  • Blurred vision
  • Loss of consciousness

Mild CO poisoning could have symptoms just like the flu or food poisoning. It is better to be on the lookout for these common symptoms to detect carbon monoxide leakage in the initial stages before things get out of hand.

So, installing a flue pipe along with a boiler that runs on fossil fuels is mandatory except for some exceptions. You would also need to install a CO alarm to detect this gas in the initial phase of leakage. Getting your boiler inspected and serviced every year by a Gas Safe registered engineer is another thing worth considering.

Reason Behind Why Electric Boilers Don’t Need a Flue

Electric boilers use electricity for central heating instead of burning oil or gas and are best suited for low demand applications. This means no harmful waste gases are produced in the process, eliminating the need for a flue.

Cost of Boiler Flues

When getting a new boiler installed, a boiler flue usually comes along with a boiler. So, its cost is nothing to be worried about. If you need to get your flue pipe replaced for some reason, buying a new one would cost you around £100.

Type of Flue Estimated Cost
Horizontal or Vertical Flues £70-£120
 Flue Pipe Extension/Flue Bends £40/metre

What is the Need for Boiler Flue Regulations?

Boiler flue regulations are in place to ensure that the best practices are adopted while installing the boilers flues.

According to these regulations, a flue should not be installed too close to the windows and doors. Installing them 30-60cm away from the windows and doors is considered acceptable under these regulations which would differ depending upon the property size.

Detecting a Blocked Flue

There is a chance that debris makes its way into the flue pipe and causes it to get blocked. If such a situation occurs, the waste gases will be unable to make their way out of your home. This could also lead to overheating of your boiler and harmful CO gases leaking back into your living area.

If your flue gets blocked, it would have devastating effects on your boiler as well as on your health. So, it is better to be proactive in approach and make getting your boiler inspected and serviced every year by an engineer a must. The engineer would ensure that your boiler and your flue pipe are working perfectly free from any obstruction.

When a fault arises in your boiler, it displays an error code corresponding to that fault and is an easy way to detect the problem. An issue with a boiler flue pipe is also depicted with an error code. Some leading boiler manufacturers along with their boiler flue error codes are listed below:

Leading Boiler Manufacturers Error Codes
Alpha 3, 25
Vaillant ecoTEC Plus F25, F77
Baxi Platinum E28
Worcester Bosch Greenstar 8000 2927 B


Why Do You Need a Flue Terminal Guard?

You would be wondering what is the use of a flue terminal guard, right? Flue terminal guard is used to prevent debris from making its way into the flue pipe. You just need to fit it over the flue pipe for debris control.

Flue Terminal Guard could cost you somewhere between £5-£45, depending on its shape and size.

Best Practices for Getting a New Boiler and Flue

If you think it is time to get your boiler and flue replaced, you should get quotes from a couple of qualified heating engineers. You should go with the one that offers you the best in terms of price and quality, giving you peace of mind that you are getting the absolute best!