We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

What is a Double Flue?

Mary McMahon
Updated: May 17, 2024

A double flue is a set of two flues which are routed out of a structure together. These types of flues are sometimes inserted into existing chimneys, and in other cases, a chimney may be designed from the start with the intent of being a double flue. For an example of what this type of flue looks like, a perusal of photographs of large mansion houses may provide some examples, as many of these structures use double flue designs to minimize the number of holes in a roof, and as a result chimney pots are often seen in pairs which emerge from the same chimney.

There are a number of reasons to use a double flue. In cases where multiple fireplaces, woodstoves, or other heating devices are attached to the same chimney, that chimney may not be able to generate enough draw to handle all of these attachments. As a result, lighting a fire upstairs might cause smoke to belch out downstairs. In these cases, enclosing a double flue inside the chimney allows for two fireplaces to be on separate flues. The design also makes it possible to cap one flue to prevent drafts when a room is closed off without impairing the function of another device connected to that chimney.

A double flue can also be used when two different types of fuel-burning devices are attached to the same chimney. For instance, someone might use a double fuel to vent an oil heater and a gas stove through the same chimney. Since different fuels combust at different temperatures, leading to differences in the temperatures of the flue gases they produce, it may be necessary to use separate flues to get an appropriate draft, or for safety reasons.

New double flue construction is popular because it provides people with flexibility and some additional options. The separate flues can be used to vent a wide variety of fuel-burning devices, and if a flue becomes unnecessary, it can be capped to minimize drafts, and uncovered later in the event that someone wants to use it.

Some special code restrictions apply to a double flue design, for safety reasons. When designing this type of flue, it's important to use a heating specialist who is familiar with flue design and the relevant codes to confirm that the flue will work efficiently while complying with the law. In the case of a modification to an existing chimney to create a dual flue, a heating professional can help the modification go smoothly and as painlessly as possible.

About Mechanics is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a About Mechanics researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

Learn more
About Mechanics, in your inbox

Our latest articles, guides, and more, delivered daily.

About Mechanics, in your inbox

Our latest articles, guides, and more, delivered daily.