Your chimney sweep might tell you that your chimney is fine and doesn't need lining but your Stove Specialist will tell you that it does. Who is right? Well, the sweep may well be correct and your chimney is sound, but wrong in saying that it doesn't need lining. Stoves have special requirements which mean that no self-respecting Hetas registered installer will install into an unlined flue without a very good reason.

Hetas and all manufacturers of quality stoves recommend that the flue serving a multi-fuel or woodburning stove should be lined as part of the installation process. There are warranty and house insurance issues with not lining and Hetas could deem an un-lined installation to be "Substandard"

The traditional British chimney was designed for open fires, not stoves. Open fires are very inefficient and send huge amounts of heat up the chimney; thouroughly heating the flue right to the top, ensuring a vigorous flue-pull.

Stoves, due to their much higher efficiency, emit only a tenth of the waste heat up the chimney. This means that the upper regions of the flue are not heated sufficiently, or at all, and cause a variety of problems:

• The flue will be "lazy", not wanting to pull, resulting in a stove which can be difficult to light, burns badly and blackens the glass.
• Smoke can spill back into the room when lighting and refuelling.
• The moisture in the flue-gasses can condense on the flue wall and, combining with tars in the flue-gasses, create creosote which runs back down the flue into the fireplace and/or on to the stove leaving a black, stinking residue which can not be removed.
• Worse, the tar can line the chimney with a hard, glassy surface impervious to sweeping. If ignited, this can burn for days. This tar can soak right through the masonary of the chimney, often seen as a black stripe up the outside of older houses, marking the route of the flue (see example). If a chimney fire occurs, this tar expands to six times it's original volume, opening up the structure and exposing ceiling and roof timbers to the fire. Houses burn down as a result!
• Small leaks in the flue, which would be unimportant with an open fire, can be sufficient to cool the flue gasses near the top of the flue enough to cause a "cold plug" stopping further upward motion. When this happens, the stove can continue smouldering but venting the carbon monoxide laden fumes directly into the room with possibly lethal results. Many people express surprise that wood or coal gives off carbon monoxide. It is a carbon based fuel, gives off many times more carbon monoxide than the equivalent gas fire and doesn't have the sophisticated carbon monoxide detection facility of a modern gas fire.

It might seem to be an un-necessary expense on something you will never see but try imagining standing in the burned-out shell of your home or at the grave-side of a loved one and you will understand why a conscientious stove specialist will insist on lining your flue.