Do I need a chimney liner for my wood burner?

If you have an existing chimney and you are planning a wood burner, you will almost certainly hear the question of lining come up. Some people are told they must line, others that they do not need to. Both can be right, because the answer depends on the chimney.

This guide explains what a liner does, when one is likely to be needed, the main types of system, and how an installer checks the chimney before deciding.

What does a chimney liner do?

A chimney liner is a continuous tube running inside your chimney from the stove to the top of the stack. It gives the smoke and gases from the stove a sound, sealed path out of the house.

A good liner helps in several ways:

• it stops fumes, including carbon monoxide, leaking through cracks in old brickwork or mortar into rooms or roof spaces
• it gives the flue a smooth, consistent bore, which helps the stove draw properly
• it can be sized to suit the stove, as many stoves are designed for a flue of a particular diameter
• it keeps flue gases warmer, which reduces condensation and tar deposits

Does every chimney need a liner?

No. There is no blanket rule that every stove must have a liner. What the regulations require is that the chimney is safe and suitable for the appliance connected to it.

As HETAS puts it, your installer must satisfy themselves that the chimney has no defects and is suitable for its intended use. If there is any risk that the chimney could leak fumes into the house, it must be lined.

In practice, many chimneys do end up being lined, especially in older houses.

When a liner is likely to be needed

HETAS notes that chimneys built before 1965 often need a modern lining. Common reasons include:

• the chimney has lost its integrity over time, with cracked or eroded mortar
• tar or condensation is seeping through the brickwork, often seen as brown staining on chimney breasts
• the flue walls are rough or damaged, which slows the draught
• the flue is too large for the stove. HETAS points out that flues over 200mm, particularly those with voids, can affect how a stove performs
• the chimney was previously lined for gas, and that liner is not suitable for solid fuel

Plenty of North East homes have chimneys well over a century old. Many were built for open coal fires and have seen decades of use, so their condition can vary a great deal even between neighbouring houses.

How the chimney is checked

Before deciding whether to line, an installer needs to know what condition the chimney is in. Approved Document J says that when a flue is being brought back into use, the flue and chimney should be checked and, if necessary, altered so that they meet the requirements.

Checks typically include:

• A visual inspection of the chimney breast, loft space and stack, looking for cracks, staining or damage
• Sweeping to remove soot and deposits. Approved Document J says flues should be swept before relining
• A smoke test, where smoke is introduced into the flue to see whether it draws properly and whether it escapes anywhere it should not, such as into a bedroom or the loft
• A check of the flue size and route, including bends, offsets and whether the flue is shared

A chimney that fails a smoke test cannot be used as it is. Lining is often the most practical way to make it safe.

Types of liner

There are several ways to line a chimney. HETAS notes there are quite a few systems available, and that flexible stainless steel is the most popular.

Flexible stainless steel liners

A flexible liner is a corrugated stainless steel tube lowered down the chimney from the top. It is connected to the stove at the bottom and finished with a terminal or cowl on the chimney pot. Because it flexes, it can follow most bends and offsets.

Liners come in different grades and diameters, and the right one depends on the stove, the fuel and the manufacturer's instructions. Approved Document J says flexible liners should only be used to reline an existing chimney, not as the primary liner of a new one, and should carry the correct designation under the relevant British Standard.

Rigid and other systems

Other options include rigid stainless steel sections for straight runs, and pumice or concrete liner systems. Some systems are cast in place inside the chimney. These are less common for a standard stove installation, and whether they are suitable depends on the chimney's shape, size and condition.

Insulation

Some installations also need insulation around the liner, for example where a chimney is on an outside wall or the stack is very exposed. Insulation keeps flue gases warm, which helps the stove draw and reduces condensation.

You can read more about our chimney liner and flue work on our services pages.

Lining and Building Regulations

Fitting a new liner alongside a stove is part of the notifiable work. It must either be carried out by an installer registered with a competent person scheme, who can self-certify it, or be approved through your council's Building Control team.

Once the stove and liner are in, the installation should be commissioned. This includes checks such as smoke, spillage and flue draught tests with the stove lit, to confirm the system is working safely. A permanent notice plate should be fitted with key details of the flue and appliance, and a carbon monoxide alarm must be fitted in the room where the stove is installed.

Looking after your liner

A liner needs care like any flue:

• burn dry, seasoned wood. Wet wood produces tar and condensation that shorten a liner's life
• have the chimney swept regularly, ideally before the heating season starts
• follow the stove manufacturer's guidance on running temperatures
• keep your carbon monoxide alarm tested and replace it when it reaches the end of its life

Not sure if your chimney needs lining?

The only way to know for certain is to have the chimney checked. If you would like us to take a look as part of a site assessment, you can request a quote and we will follow up with a written quote setting out what your chimney needs.