What size flue liner do I need for a woodburner?

When buying a woodburner, a key consideration is making sure you get the right size flue liner for your stove.

There is no standard size for wood-burning stove flue liners. Different appliances need different sizes of flue liner, so it is important to get the correct flue liner.

Understanding flue liner sizes

Flue liner sizes are usually given in inches. The figure given refers to the diameter of the flue liner. Specifically, it refers to the internal diameter of the flue liner (in other words, the size of the hole, not the size of the liner itself).

Your woodburner, or the woodburner you’re planning to buy, will also have a flue size. If you’re buying or have bought a stove from us, you’ll find this information on the stove flue size on the Specification tab of each product page. This refers to the internal diameter of the collar, which is the flue outlet on the top or rear of the stove.

While flue liner is available to buy in various sizes, including 5-inch, 6-inch, 7-inch, 8-inch and 9-inch, the vast majority of stove installations involve either 5–inch or 6-inch flue liners.

[It is worth remembering at this point the importance of making sure the flue liner you buy is of the correct grade as well as the correct size. Make sure it is either 316 or 904 grade (the two grades of flue liner suitable for use with stoves – 904 is recommended for multi-fuel stoves).

What size flue liner should I buy?

Usually, you will buy the flue liner of the corresponding size to the outlet on your stove. If your woodburner has a 6-inch outlet, you would buy a 6-inch stove liner.

Under the Building Regulations, the minimum flue liner size you can use is 6 inches (150mm). But there are exceptions to this rule.

You can use a 5-inch (125mm) flue liner with a stove that has a 5-inch if either of the following applies:

• You will only be burning smokeless fuel.
• Your stove has DEFRA exempt status for burning wood.

If you want to burn wood in an appliance that has a 5-inch outlet, you will need to install a 6-inch flue liner. There is a range of flue adaptors that will allow you to do that.

You can step up in size as required, but you can’t step down. For instance, you couldn’t do the reverse and attach a 5-inch liner to a 6-inch outlet and pipe. That would prevent gases from being drawn up the flue correctly.

It’s also worth saying that the flue liner you fit should never be less than the minimum stated by the stove manufacturer. If the manufacturer says it needs to be 7 inches, it needs to be at least 7 inches. Check your stove manual for guidance on this.

The other size consideration when buying flue liner is the length. You can find out how to buy the correct length of flue liner for your woodburner in this article.