Why most chimneys need a liner
Chimney liners are strongly recommended when installing a new stove, especially if you are using an old chimney. The chimney must be
checked for condition and suitability and you must also ensure that it is swept before the stove and liner is installed, even if the chimney has never been used. So, why would you need to fit a liner?
There are two main reasons – firstly and most importantly, safety and secondly, to ensure the efficient operation of the stove. This is usually because of the following…
• The chimney is often regarded as the ‘engine’ of the stove. Anything less than a good one will not provide the vital updraught needed to ensure your stove operates safely and efficiently, whilst at the same time helping to minimise the amount of smoke and particulates produced. A correctly fitted flue liner is a major ‘quantifiable’ component in your stove installation reducing, and making it easier to
identify, any potential operational problems or safety issues for the installer, stove dealer, stove manufacturer and chimney sweep.
• An old unlined chimney could leak smoke and deadly invisible carbon monoxide (CO). Leaks occur because of the failure over time of the
mortar bonds and mid-feathers (the dividing brick wall between different chimneys using the same chimney breast) due to acidic condensation from years of coal burning. Flue gases from open fires
are much cooler than those exiting from a stove so these faults may only become apparent once a stove is fitted.
• Without a liner, condensation or creosote, associated with burning wood, could eventually seep through the chimney walls, particularly if
they are made of old or porous brick and / or are jointed with lime mortar, eventually causing unsightly stains on decorative coverings or
exterior render.
• Even houses built since 1965 with clay or concrete chimney liners could suffer from leaks. These type of liners are often poorly installed, either through being fitted the wrong way up or not
receiving an appropriate application of mortar to make a complete seal on each of the many joints. A case of out of sight out of mind. Even though the chimney may not be particularly old, this could still
potentially allow smoke and fumes or unsightly condensation stains to leak through decor, brickwork or rendering.
• Stoves are tested with a 12Pa flue draught and they work best with this updraught. Pre-1965 chimneys which have been built for open fires
will have larger (and often irregular shaped) voids than those best suited for a modern stove and this could reduce the effectiveness of the flue updraught by, for example, making the flue too cold and difficult to warm. This in turn can cool the flue gases towards the top to the point where under certain weather conditions a cold ‘plug’
is created which could cause smoke to enter the room. Problems with cold and difficult to warm chimneys can be exacerbated if the chimney
breast is on an outside wall and / or is subject to a strong prevailing wind.
• Unlike a large uneven chimney void a chimney liner will provide a flue diameter consistent with the stove’s flue outlet as well as a smooth flowing regular inner surface. This will minimise interference to the updraught and help the flue gases to exit quickly without cooling significantly and avoiding the creation of condensation
towards the top of the chimney. When back-filled with vermiculite or sheathed with a purpose-made Insulation wrap a liner will keep flue
gases even hotter. This all helps to improve the stove’s safe operation and to minimise the amount of smoke produced.
