WHY SHOULD A CHIMNEY BE LINED
For a stove to work successfully it must be connected to a sound chimney and properly sized flue.
The purpose of a chimney is to remove the products of combustion from the appliance to the outside without causing harm to the occupants or risk of setting the house on fire.
A chimney works on a simple rule hot air rises therefore the flue should be well insulated for this to happen.
Before going any further it is important to understand the terms that are used.
Operating a stove at a low temperature for long periods or cold air leaking into the flue, will cool the flue gases down and affect the performance of the chimney. To keep the flue gases warm, proper thought must be given to the insulation properties of the lining within the chimney.
Before flue liners were ever manufactured flues were usually parged on the inside with mortar. This parging over a period of time would have deteriorated from the corrosive properties within the flue gases, resulting in deteroration and leakage. This can usually be noticed by a sandy-powder like material falling down inside the chimney .That sandy material would be the plaster that has deteriorated over a period of time also the mortar between the bricks will have deteriorated in the same way.
Chimneys are often constructed on the outside of the house and are exposed to the elements. This combined with the fact that there might be no insulation around the flue liners all adds up to a cold flue.
Remembering that stoves are efficient heating appliances and will produce up to 80% of heat from the fuel being used into the room, not like an open fire that can loose up to 75% of the heat. With little heat loss from an efficient stove it becomes understandable how important it becomes to maintain a reasonable flue gas temperature in order to achieve the proper draft.
A properly lined and well insulated flue will produce a safe and efficient appliance. Unlined chimney flues can result in very costly rebuilding of the chimney and/or your home.
REASONS TO LINE
There are a number of reasons why a chimney should be lined or relined: