The Advantages of Twin Flue Boilers

Twin flue boilers are perfect for installations that demand flexibility above all else, especially when a traditional concentric flue just won’t cut it. You can really take the stress out of a situation with twin flue boilers, giving you more choice when siting boilers in tricky commercial or domestic settings.

The key advantage for your installation if you opt for a twin flue boiler — especially when tackling more unusual central heating jobs — is a longer flue run. This gives you more options whether you’re fitting combi boilers in homes or something larger in a commercial setting, removing the need to flue them concentrically through the nearest external wall or roof.

In this blog post we’ll explain why these flexible types of gas boiler flues could be just the ticket for your next installation job.

Explaining the Meaning of a ‘Twin Flue Boiler’

First things first — here’s a brief explanation of how twin flue boilers work and what sets them apart from other types of gas boiler flues.

How Do Concentric Flues Work?

Boilers in most homes use a concentric flue, a pipe within a pipe, as a one-piece system to take care of both the flow of air supply into the appliance and the removal of flue gases out of the appliance.

These flues generally have an overall diameter of 100-150mm and run up to 10 metres, either horizontally or vertically, although the majority of installations won’t run anywhere near as far. Waste gases are channelled away through the inner flue (the boiler waste pipe), while the air used in the combustion process arrives through the outer flue.

Why Twin Flue Boilers are Different

A twin flue boiler system does the same job but with greater flexibility and less compromises, as the air intake and exhaust flue pipes are separate and generally of a smaller diameter than a concentric system. With the flue runs no longer bound together concentrically, you can install a boiler almost anywhere in a building.

In fact, twin flue systems like Keston's System S30 allow you to run the flue vertically or horizontally and extend the flue up to 27m from the boiler, giving you far more flexibility when it comes to siting the appliance.

The Benefits of Flexible Boiler Flue Outlets

With the air intake and the exhaust flue separated, installing a twin flue boiler means there's no longer a need for them to run parallel to each other. They can have different termination points and their runs no longer have to be the same length.

To sum up one of the most useful benefits of a twin flue, your air intake can come from the closest external wall while your combustion pipe can run to a termination point much further away. With a Keston model, the range is up to 27m from where the boiler is sited — almost three times the maximum distance of a concentric flue and much more flexible.

Planning to Install a Boiler in a Basement?

With the help of a twin flue boiler, we can install a boiler in rooms and spaces where it might otherwise have been impossible. Whether you’re working in a basement or a plant room with no external wall, this option is a great choice when you need a long flue run.

If you need a higher output, frame and header kits are available for modular (cascade) boiler installations. Looking at our Keston Heat 2 Cascade as an example, you can count on a maximum output of 330kW.

Does My Boiler Need to Be on an External Wall?

Although boilers in homes will most commonly be fitted on an external wall, meaning the flue can be directed outside quickly and easily, not every installation is that straightforward. Twin flue boilers offer a handy solution when fitting to an external wall just isn’t an option.

These appliances allow you to run the flue either horizontally or vertically, with the air intake and exhaust flue not bound together as they aren’t using a concentric system. So what sort of situations might be suited to using a twin flue boiler?

Installations that Can Benefit with Twin Flue Boilers

Every gas engineer will have their stories of tricky installations, covering everything from colleges to Grade II listed buildings. Relocating the boiler in any building can be an expensive and time-consuming job, whereas using a twin flue boiler to provide additional length is a much simpler and cost-effective solution.

Complying with boiler flue regulations can be another key reason for choosing to use a twin flue boiler. For example, flueing from the nearest possible wall may not be possible if it’s in close proximity to a window or external door. In this case, using a twin flue boiler will allow you to site the appliance in a convenient space while still being able to be compliant with the position of the termination point.

Maybe you’ve been asked to hide the flue to maintain the external appearance of a building, or just need to create an unusual run to accommodate a central heating system. A twin flue boiler is a great option in these circumstances, and many more in between.

Can You Have a Twin Flue Combi Boiler?

When it comes to twin flue boilers, the flexibility on offer doesn’t stop at having the option to site a boiler in different rooms. Depending on the circumstances and the unique needs of each property, you may want to install a system, heat only or combi twin flue boiler. At Keston we offer all three types of appliance, meaning there’s a central heating solution available for every application.

For more information about how a Keston twin flue boiler can make every job easier, head to our page Why Keston?, and you can find in-depth case studies on the Keston news hub.