LINING OLD CHIMNEYS

The most appealing focal point in any room must be the fireplace. Be it an open fire, closed stove or solid fuel effect gas fire, the leaping flames and glowing coals are the real heart of the home.

However, for any fire to work successfully, it must be connected to a sound chimney and correctly sized flue. The functions of a chimney are to safely remove the products of combustion from the fireplace or appliance to outside without causing danger to the occupants of the house or risk setting the house itself on fire.

A chimney works because hot air rises. Factors such as running the appliance at a very slow rate or cold air leaking into the flue will cool the gases down and affect the performance of the chimney. To keep the flue gases warm, consideration must be given to the insulation value of the lining system chosen. In houses built since the introduction of the 1965 Building Regulations, all flues have to be built with liners during their construction. This is usually done with clay liners, which should last the life of the building. However, in houses built prior to 1965 lining was less common.

Flues were usually “parged” (rendered) on the inside with lime mortar. This parging suffers attack from acids and tars produced during combustion and gradually deteriorates. The flue is then in poor condition, often leaking fumes or tars into the walls or other parts of the building. Sadly, many houses built since 1965 also suffer similar problems due to badly installed flue liners and need further attention.

DEFINITIONS

Before proceeding further, it is important to understand the terms used when talking about chimneys. These are briefly as follows:

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 flues.

3. FLUE LINER – The flue liner is the material used to form the flue or flues within a chimney.

REASONS FOR LINING

There are a number of reasons why an old chimney may need lining. These can be summarised as follows:

1) The flue is leaking smoke and fumes into other rooms or parts of the building.
2) Condensates or tar are seeping through the chimney walls causing staining either inside or outside the building (a common problem with wood burning stoves).
3) The flue is much too large for the type of fire or appliance being used.
4) The flue is too cold, particularly if on an outside wall, and is consequently not drawing properly.
5) If the chimney was built since 1965, but with the liners installed the wrong way up (regrettably this is quite a common occurrence!) tar and condensate leakage may occur.
6) The old flue surface is eroded and rough causing frictional resistance to the flow of the flue gases and resulting in poor updraft.
7) When a new gas fire is installed to an unlined chimney, lining should be considered if the old parging is crumbling with mortar debris continually falling onto the hearth, or if there is evidence of condensation. (see BS5440 pt. 1 -4. 1 .9.).

Click on the ‘Technical Guide’ tab in this link to find more detailed information on:

METHODS OF LINING
RIGID REFRACTORY LINERS
PUMPED REFRACTORY CONCRETE
RIGID METAL LINERS
FLEXIBLE METAL LINERS
INSULATION
FLUE SIZING
CHIMNEY TERMINATION

NOTE: Any person carrying out work to a gas appliance installation, which includes work to flues and chimney terminations, must be registered with CORGI. This is a legal requirement of the Gas Safety (Installation & Use) regulations 1984 (1990 amendment).