Are you curious about Baxi’s twin flue system?

Many of my customers come to me asking about the advantages of a twin flue, as Baxi is the only big brand domestic boiler manufacturer to offer this system – it’s one of their main USPs.

And having installed countless Baxi boilers over the years, I know first-hand what a difference it can make – especially in situations which might otherwise be awkward.

If you’re not sure you need a twin flue, or want to find out what it actually means, you’re in luck; I’m going to explain all in this blog post.

What is a twin flue?

Normally, a standard flue can run vertically and terminate through the roof, or it can run horizontally with a standard flue kit (100mm diameter) up to 10 metres.

A larger diameter flue kit (125mm) can run up to 20 metres – or with a twin flue pipe (80/80mm), it could run a distance of up to 15 metres.

As a twin flue system is only 80mm in diameter, it can be fitted in ceiling voids if, say, you want to locate your boiler in an internal cupboard. This is a huge advantage, as most ceiling voids cannot accommodate a 125mm flue duct and brackets.

What does it mean for you?

Baxi’s twin flue system essentially gives you more options when it comes to choosing a new location for your new boiler.

You could have the potential to have a boiler installed long distances from an outside wall – in places where it might otherwise be impossible to fit a premium brand boiler such as Vaillant or Worcester Bosch.

We’ve fitted Baxi twin flues twice in the past year, in situations where it was the only financially viable solution. It also meant the work could be completed in just one day.

Also, in one instance, keeping the boiler in the same location and supplying and fitting the long flue worked out £1000 cheaper than an alternative company who wanted to relocate the boiler.

Do you need a twin flue?

All boilers come naked (not in a calendar girl sort of way), and the flue size your boiler needs will be dictated by the route it needs to take to exit the roof or wall.

This means your Gas Safe registered heating engineer will have to calculate how many flue extensions, bends and brackets are required. Also, when fitting a twin flue system this may be concealed in a ceiling or void, so joinery work or decoration will be another cost factor involved.

TIP: Always make sure you ask your engineer how much extra damage or decoration will be needed before making your final decision.

Remember, if your boiler is in a hall cupboard and the flue passes through the ceiling in the hall and bedroom, your engineer will have to cut hatches into the ceiling to fit the flue pipe. Inspection hatches will also have to be installed in the ceiling at joints for service inspections and testing.


If you’re wondering whether Baxi’s twin flue system could make a boiler installation easier in your home, this blog may be able to help explain the situations where this type of flue may be necessary or desired.

A twin flue could potentially allow you to install your boiler much further away from an outside wall, or give you more options when it comes to choosing a new location for your boiler.

In order to find out if you need a twin flue, your chosen heating engineer will first need to calculate how many flue extensions, bends and brackets are needed for your boiler. You may also have to factor in joinery work or decoration in the overall costs.

Would a twin flue make life easier for you?