Economics
March 20, 2015
Building Health
April 9, 2015

Trouble with Chimneys?

Many people are choosing to remove unused chimney breasts from their homes to create more usable space. However some people like the idea of keeping the chimney and having an open fire. If you have a fire you need to ensure that the chimney is working properly.

Chimneys operate on the principle that hot air rises because it is less dense than cold air. The hot air in a chimney rises as it is less dense than the air outside the house. The rising hot gas creates a pressure difference called draft which draws combustion air into the appliance and expels the exhaust gas up and out through the chimney top.

Two factors affect the amount of draft produced by a chimney.
1. Heat: the hotter the gases in the chimney compared to the air outside, the stronger the draft.
2. Height: the taller the chimney, the more draft it will produce at a given temperature difference.

Here are some of the problems which are the result of inefficient or deteriorating chimneys.
The fire is not drawing properly – This is often the result of a cold flue or an obstructed flue, or it can arise from a chimney that is too short. Sometimes double glazing and very efficient draught excluders around doors, etc, may prevent an adequate flow of air for the fire and chimney to work correctly.

The fire creates excessive soot – This usually means an inefficient flue. 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.

Mortar/debris falls into the fireplace – Bits of brick or mortar falling down the flue indicate a serious deterioration in the chimney structure. Such degradation normally happens inside the flue but if there is any indication of weakness on the outside of the chimney then attention is necessary.

There are fumes in the rooms – It is normally easy to spot when smoke comes into the room, but fumes are more difficult to detect. When organic materials such as wood or coal are burned they produce carbon monoxide which is poisonous. Look out for smoke stains on walls or carpets which may indicate 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 – Large uninsulated flues require a lot of heat and fuel to make them draw. An insulated flue of the correct size is required to ensure that an adequate draught is created for them to burn as their designers intended. Otherwise they will use too much fuel and the slow moving fumes will also condense into acids which can attack the internal surface of the chimney.

If you are considering opening a chimney that has not been used for some time, please ensure that you get it thoroughly checked.

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