Flue Liner Considerations  

The choice of  flues need to take into account many considerations.Flue temperature inside the chimney- What temperature the flue is designed to withstand.

Heat resistance and thermal stresses.

Acid resistance - Acid will build up in the flue and some flues are better at resisting acid build up than others.

Shape and size of the flue - This will be determined by building regulations.

Most modern flue liner systems are insulated to preserve the flue gases temperature and have been time-tested to resist the higher temperatures effectively thus reducing significantly the risk of soot fires in the chimney. These fires will prove the sternest test for flue liners as they burn at the highest temperatures a flue will encounter. A flue will be put through thermal stresses every time it is heated by the fire. In essence the flue will be forced to expand when at it's hottest and contract when colder. The weak point in a flue lining is the joints inside the chimney, so if at all possible try and by one who section of flue to help prevent the problem. In addition using one piece of flexible flue will stop soot accumulating in corners and edges of joints.

In liquid fuel, such as oil and gas, the gases generally are heated at lower temperatures and soot in the chimney is not so much of a problem. However, this creates a different problem as the gases cool quicker and often in the flue. This causes acid to build up in the chimney which can eat away at the flue lining so look at the acid resistance of each flue before buying.

The troubles with flues could have little to do with the chimney, building or appliances. Close by trees or adjoining tall constructions can change the wind flow with the effect of causing turbulence across the flue terminal on top of the chimney or worse still allow the gases to blow back down the flue and into the building. This can be established if you witness irregular whiffs of smoke in the room.

Building Regulations

The laws for the design and manufacture of chimneys in England and Wales are given in Part J: 2002 Edition - Combustion appliances and fuel storage systems.

In Scotland, the prerequisites are in Part F of the Building Standards.

In Northern Ireland the requirements are in Technical Booklet L, Building Regulations (Northern Ireland) 1990.

The rules state the common necessities for appliances and chimneys. These are unambiguous and frank requirements, including sufficient air draw, combustion gas safe emission and building fire protection.

Other requirements in England and Wales are abiding by a checklist outlining how the manufacture of the flue liner and chimney ought to be accomplished.

Document J gives details of the lowest flue sizes accepted for different building and appliance sizes. It is crucial to use the right size flue. If it is too small then the flue will not draw properly and won't take e the smoke and gasses away from the building. If the flue is too large the draw can be disturbed leading to tar and acid build up which can shorten the life cycle of the flue liner.