Flues are pipes or ducts which carry waste gasses away from a building to the air outside. This can be caused by two possible mechanisms
- the exhaust gasses are hot and rise naturally up the flue by convection (as with a wood burning stove or conventional gas fire)
- the gasses are expelled mechanically by a fan (as with balanced flue gas boilers)
With balanced flue boilers there are clear limitations and instructions which come with the boiler concerning how the flue should be installed. The maximum length of flue varies considerably from model to model. Some need to be positioned so that the flue goes directly through the wall to the outside while others can have several metres of flue which allow the boiler or heater to be positioned on an internal wall.
In the case of convection driven appliances there is a whole range of materials and configurations which are possible. The main considerations are covered in the Building Regulations, part J. These include:
- masonry chimneys and the types of flue liner they require. (also covers change of use, for instance if you are splitting a building into two flats)
- flueblock chimneys
- connections for flue pipes
- repairing and reusing flues This includes testing old flues and types of liner
- factory made metal chimneys
- running factory made chimneys through combustible areas such as floors and ceilings, cupboards etc
- bends in flues
- openings for inspection and cleaning
- low level flues near boundaries
- sealing gaps around fireplaces
- testing, responsibility and notice plates
