The correct chimney terminal is essential for your appliance/ chimney to work safely and efficiently. There are many types designed for different purposes. One of the most common faults is an incorrect terminal.
A chimney pot is an integral part of any masonry chimney system. Chimney pots have been used in Britain since at least the 13th Century. They are usually made of terracotta and sit on top of a chimney. Chimney pots can be round, square, octagonal, or rectangular but, in all cases, they are open at the bottom, where they attach to the chimney and open or vented at the top.
Purposes of chimney pots
• Increase the speed smoke rises by reducing the size of the outlet – warm air rises so this ‘bottleneck’ can create a jet-like effect.
• The reduction in the size of the opening reduces the entry of rain and downdrafts of air that can prevent the smoke leaving the building.
• Openings in the pot – like louvres and grills – can promote cross-drafts at the top, which also serve to increase the flow of smoke up the chimney.
• Raise the height of a chimney – If the chimney terminates above adjacent buildings or roofs it will perform better. Sometimes the easiest way to raise the height can be to fit a tall pot.
A chimney pot should not be set directly on top of the brickwork but should be bedded into the top of the stack to ensure it has adequate stability in high winds.
A chimney cowl is usually a metal object that is fitted to the chimney pot or flue with the fundamental purpose of improving the performance of the flue.
The main reasons to fit a cowl
• The chimney is affected by ‘down-draught’; this is when air is being forced down the chimney, usually caused by wind flow.
• Birds nesting or entering the chimney – birds love nesting in chimneys and can return even if the nest has been removed.
• Rain entry – rain can cause damp issues or staining in the fireplace.
• Improve draught – the speed of which gasses are evacuated is vital. Some cowls are designed to improve the chimney draught.
• Cap a disused flue – if a fireplace is unused, it is a good idea to cap the top to stop heat loss and birds nesting or entering.
There are a huge selection of chimney pots and cowls, the type of appliance will dictate the type of terminal that can be used. It is important to identify the fuel type of the appliance; most terminals are only suitable for certain fuels.
A professional chimney sweep will be able to diagnose problems and advise any remedial work required to the chimney terminal. To make any changes will involve working at height and hugely affect the performance of the flue, a competent person must undertake this type of work.