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Chimney Liner Sizing Guide

Chimney Liner Sizing Guide

Perhaps you’ve just bought a new fire or stove, or you’re experiencing venting problems with your chimney, or maybe you haven’t had your chimney inspected in years. These are just a few of the reasons why you might need to buy a new chimney liner. But do you know what size chimney liner you require? Read our chimney liner sizing guide to find out now.

What is a chimney liner and why do you need one?

Before we dive into the details of different chimney liner sizes, we’ll first of all establish what a chimney is, what it does and why it’s important to have one.

A chimney liner (also referred to as a flue liner) is basically a long pipe or conduit made of metal (although ceramic and other materials are sometimes used) that is installed inside of a chimney to do three things:

  • Contain smoke and combustibles.
  • To safely channel the smoke and combustibles out of your home.
  • To protect the walls of your chimney from corrosion and damage.

Flue liners are recommended by installers, as they not only help draw away smoke and combustibles from your appliance, but they can improve its performance and safety too.

It is recommended that you buy and install a new chimney liner whenever you buy a new stove or fire - you want to ensure that you have a chimney liner which is compatible with your new appliance.

Another consideration is the lifespan of your current chimney liner. Good quality stainless steel liners will generally last between 15 and 20 years. If you’re not sure how old your current chimney liner is, replace it.

If you’re unsure if you need a new chimney liner, contact your local chimney sweep or chimney inspector who will be able to tell you.

Picking the correct grade chimney liner

Shop Now: 6” Super Flex Gas Chimney Flue Liner.

Not only will you need to select the correct size chimney liner, but you will need to select the correct grade chimney liner.

What grade liner you will need will be determined by what type of appliance you will be attaching it to.

Gas chimney liners

If you are installing a new gas appliance then you’ll need to install a gas-specific liner. These are often referred to as single skin liners or 316 grade.

Gas liners differ from other types of chimney liners as they are only single ply, making them lighter and less expensive. Using a liner with a gas fire will help channel away exhaust fumes and prevent potentially harmful carbon monoxide leaks.

You must never use single skin gas flue liners with wood or multi fuel burning appliances.

Multi fuel liners

If you are installing a multi fuel appliance - that burns wood, coal or other forms of solid fuel - then you will require a multi fuel liner. These liners are often referred to as twin skin liners or 904 grade.

Multi fuel liners are manufactured from overlapping strips of high grade stainless steel to create a smooth, sealed flue way. Thanks to their twin skin construction multi-fuel liners are able to handle the much higher temperatures (and harsher combustibles) that come from burning wood, coal and other solid fuels.

Picking the correct diameter chimney liner for your appliance

Shop Now:7” 904/904 Super Flex Chimney Flue Liner Full Fitting Kit.

Once you’ve determined which grade liner you need, you should next look at what diameter you will need.

The diameter of your chimney liner will be determined by the heat output and/or the size of the connector collar of your appliance.

What diameter chimney liner should I use for multi fuel appliances?

For multi-fuel burning appliances, the size of the chimney liner will be determined by the heat output of the appliance. For example, if you have purchased a wood burning stove with a heat output of up to 20kW you will require a chimney liner that is at least 6” in diameter.

For multi-fuel appliances with much higher heat outputs, you can purchase flue liners as big as 7”, 8” and 9” inches in diameter.

If you have purchased a DEFRA approved stove or appliance, then you may use a 5” diameter flue liner.

Note - Your appliance may have a smaller collar than your required chimney liner. For example, your appliance may have a 5” inch connector collar while you need to use a 6” inch chimney liner. If this is the case, simply purchase a connector which will allow you to easily connect your appliance to your chimney liner.

What diameter chimney liner should I use for gas appliances?

Gas appliances generally use 5” or 6” inch chimney liners. The size of liner that you need for your gas appliance is usually determined by the size of the connector collar on the appliance. For example, if you have a 6” inch connector collar on your gas fire, then you’ll need to buy a 6” inch chimney liner.

Many gas appliances will come with information on what size and grade chimney liners they are compatible with.

As the British Flue & Chimney Manufacturers Association (BFCMA) puts it:

“It is important to match the internal diameter of the flue with the outlet on the appliance. It should never be less than the outlet diameter of the appliance. The appliance manufacturer’s chimney sizing recommendations should always be followed.”

Picking the correct length chimney liner for your appliance

Once you’ve determined the grade and diameter of your chimney liner, you will need to select the length.

The easiest way to determine what length chimney liner you will need to buy is to enlist the help of your nearest chimney sweep. A chimney sweep will usually combine the measurement of your chimney and a chimney clean in one job - so, you can get better value for money. Although, you should tell the chimney sweep that you want them to measure the chimney before they start cleaning it.

A chimney liner must stretch the entire height of the chimney - from the connection on the appliance, to the top of the chimney, so getting an accurate measurement is important.

If you’re in any doubt, it’s safer to order your chimney liner a bit longer than you need. It can always be cut down. If your chimney liner is too short, you cannot connect two separate liners together. This is dangerous and will lead to problems in the future.

Here at Trade Price Flues, you can order our chimney liners by the metre, so you can get the exact length you need to fit your chimney.

If you’re looking for a chimney liner for your appliance, explore the huge range at Trade Price Flues now.

If you’d like some free advice about chimney liners then contact us or use our live chat (you’ll find it on the bottom right of this screen) and we’ll be happy to provide you with our expert advice.

More buying guides and advice you might like...


How Do You Fit a Chimney Liner? | Does My Chimney Need a Liner? |
Do You Need a Chimney Cowl on Your Chimney?

29th Mar 2021 Trade Price Flues

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