Boiler flues: What is a vertical flue? What is a horizontal flue?

Lets start by explaining exactly what a boiler flue is, and it’s not tricky. Put simply a flue is a tube that runs away from your boiler to the outside of your home and gets rid of harmful gases, such as carbon monoxide.

As Gas Safe Registered engineers we have strict regulations to meet when installing your new boiler flue, such as where the flue is positioned. As a result, the type of flue you have currently may influence your decision on where to install your new boiler. Let’s break this down in a little more detail.

Horizontal boiler flue
The horizontal boiler flue is the most common type of flue and what we see during the majority of boiler installs around the North East. In a nutshell, if your current flue pops out of the wall behind your boiler (horizontally) then a new horizontal flue will be installed when you replace your boiler, assuming your new boiler is going in the same place as your old boiler.

More often than not, if your boiler is less than 15 years old it will have a horizontal boiler flue. To find out for sure, nip outside and take a look at the outside wall where your boiler is located, if a pipe pops out then you have a horizontal flue.

Vertical boiler flue
A vertical boiler flue on the other-hand tends to be found in homes where the boiler isn’t on an outside wall, or when the property is a more unusual shape. Both reasons make it tricky to run a flue out of the wall straight in to the open air, like we do with a horizontal flue. Instead we might run the boiler flue up and out of the roof vertically, hence the name, vertical flue, and if needed sometimes around corners and other obstacles until we get outside.

Vertical boiler flue

How much does a boiler flue cost to install?
Your new boiler flue will be built in to your boiler install package price so you don’t have to worry about this being an additional cost.

The installation of a vertical flue can cost a little more than the installation of a horizontal flue. The reason being is the extra parts needed and the extra time needed to install a vertical flue compared to that of a horizontal flue.

Another important factor to consider is that extra equipment, such as roof ladders or scaffolding might be needed if the flue is high and/or on a pitched roof. In some cases a roofer may be arranged too and if the new flue is a different shape to the old flue, maybe the old flue was larger and square and the new flue is smaller and round, there may be need to brick up any gaps. This is all very common and would be discussed in advance. Once again the cost would be included in the boiler package price and never added on unexpectedly.

How do I know if my boiler has a flue?
There are three main boiler types, a regular boiler, a combi boiler and a system boiler. You will definitely have a boiler flue if you have one of these three boilers. There are also boilers that use an open flue which sucks in air from inside the room instead of from outside, in this case there will be a boiler vent as well as a boiler flue.

It is only boilers that are installed behind fireplaces, that don’t need an additional flue. This boiler type is called a back boiler and instead it uses a chimney and a flue liner to get rid of the gases so you won’t see a separate flue poking out of the wall or roof like you will if you have a one of the main boiler types.

What is the difference between a round boiler flue and a square boiler flue? 
Older boilers have square boiler flues and boilers less than 15 years old are likely to have a round boiler flue. We like to know what shape your boiler flue is as it helps us gauge the age and style of your current heating system as well as the size of the gas pipe being used. A square flue usually means an older system with a small 15mm gas pipe. A gas upgrade to a 22mm gas pipe would be needed to meet modern Gas Safe regulations.

Important boiler flue safety
Gas Safe advise that you have your boiler serviced annually by a qualified Gas Safe Registered engineer to make sure that your boiler and flue are in safe, working order and running efficiently. If you have any cause for concern, or are worried about carbon monoxide, get in touch with us as soon as possible so we can check things out.

It is worth noting that the NHS record 60 deaths from accidental carbon monoxide poisoning in England and Wales each year. With this in mind, its good to be aware of what the symptoms of carbon monoxide poisoning are, as they’re not always obvious and can be similar to symptoms of food poisoning and flu.

What are carbon monoxide poising symptoms?
A tension-type headache is the most common symptom of mild carbon monoxide poisoning. Other symptoms include:

  • Dizziness
  • Feeling and being sick
  • Firedness and confusion
  • Stomach pain
  • Shortness of breath and difficulty breathing

Call us immediately on 0191 289 3464 if you’re worried about carbon monoxide exposure in your home and seek advice from your GP.

We fit new boilers and of course new flues. Get a fixed price new boiler quote now, or drop us a message today to book an appointment with a boiler installation expert.

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