Fire is Not Drawing Properly
This is usually the result of a cold or an obstructed flue or it can arise from insufficient height relative to the ridge of the roof or an adjacent building. Large unnecessary voids at the base of the chimney may also stop the fire drawing properly. Sometimes double glazing and very efficient draught excluders around doors, etc, may prevent an adequate flow of air for the fire to work correctly.
This usually means a lazy and inefficient flue although some bituminous coals are particularly prone to this. Such a flue may not be the right diameter for the fire or stove, or may not be satisfactorily insulated so that the fumes do not rise fast enough and therefore create soot deposits. Excessive soot and tar can be a considerable fire hazard, particularly if the chimney structure has deteriorated; or where, on 19th century property for example, floor joists have been built into the stack, when the whole house can be at risk.
Mortar Falling Into The Fireplace
Bits of brick or mortar falling down the flue indicate a serious deterioration in the chimney structure. Such deterioration normally occurs from the inside of the flue but if there is any indication of weakness on the outside of the chimney then attention is obviously necessary.
Fumes In The Room
These may not be easily detected on closed appliances although if, with an open fire, the chimney smokes back into the room they are then obvious. Fumes contain carbon monoxide and are dangerous. Where there are leaks in the chimney the fumes can find their way into upstairs rooms and attics. Sometimes a tell-tale smoke stain around the edge of a carpet shows the presence of fumes.
The Chimney Breast Feels Hot
This means that the chimney has deteriorated and may be dangerous. A hot wall in the room above may be a similar symptom. If stains also appear on the chimney breast this is a sign that tar or acids have condensed and are eating into the chimney mortar and brickwork.
The Fire or Stove Is Using Too Much Fuel