Principles of Construction

Principles of Construction

Incomplete Work

1) FLUE - The flue is the void or passageway through which the

products of combustion are removed from the fire to the outside.

2) CHIMNEY - A chimney is the structure surrounding one or more

separate flues.

3) FLUE PIPE - A flue pipe is a single skin metal pipe used to

connect a fire or appliance to a chimney.

4) FLUE LINER - The flue liner is the material used to form the flue

within the chimney. Flue liners can be of fire clay, refractory

quality concrete or metal (usually high grade stainless steel).

How a flue works.

A flue is basically a column of hot air and gases, which is lighter

than an equivalent column of cold air outside.

Flues should ideally be vertical. If an offset is necessary, it should

be as near vertical in angle as possible. 30 degrees from the vertical

is the recommended maximum. 45 degrees bends are really too steep,

although permitted in some circumstances.

Flues should be insulated to keep the gases warmer therefore improving

the 'draw' and the clearance of smoke from the fireplace or appliance.

Flue Functions.

For most wood and coal fires the flue has two jobs to do:

1) To clear the products of combustion from the fire and to

discharge them outside the building.

2) To create a flow of air through the burning fire bed to provide

sufficient oxygen for the efficient combustion of the fuel (this

second purpose is often overlooked.)

For most gas fires however only 1) above is essential. It is generally

not desirable for the flue to pull air through the burner. Hence most

open-flued gas fires are fitted with some form of draught breaker or

diverter. (This reduces flue pull and ensures any down draught does

not enter the combustion chamber and blow the flame out.)

Hearth: This is basically the floor of the fireplace where the grate