Chimney cowls and terminals. “Part one”.
Over the past few years we have come across a vast array of chimney cowls and terminals. Some are factory made and others of the home made variety. A professionally made cowl or terminal is designed with a specific use in mind and should only be used for that use.
One of the most commonly misused terminals is the Bonnet Insert or Half Round terminal as it is sometimes known.
See picture (1) below: Bonnet Insert
The Bonnet Insert terminal is for ventilating a chimney flue which is NOT IN USE and under no circumstances should it be left in-situ when using an open fire, wood burning stove or gas fire. Sometimes the Bonnet Insert can be mistaken for the Chimney Pot Directional Terminal which is a one piece terracotta chimney pot which to the untrained eye does look very similar.
See picture (2) below: Chimney Pot Directional Terminal. DFE
The difference between these two illustrated terminals is that the bonnet insert in picture (1) sits inside the top of an ordinary chimney pot forming a two piece system and the chimney pot directional terminal is of a one piece system which sits on the top of your chimney stack and is kept in place via flaunching as is an ordinary standard chimney pot.
As the bonnet Insert terminal sits inside the standard chimney pot it reduces the internal diameter size of the pot itself and forms a restrictive ridge internally which in turn leads to an area where the likes of creosote and tar can accumulate as smoke reaches the coldest part of your chimney flue system if used. The lowness of the bonnet insert’s hood also captures the creosote and tars and this will, in time, become totally blocked if not removed. It is impossible for the professional chimney sweep to clean a chimney thoroughly with a bonnet insert terminal in-situ and if your sweep tells you differently it may be wise for you to seek the services of another! If you compare the two terminals shown above you will notice the difference in designs. The chimney pot directional terminal DFE has an almost round exit on either side and the height of the terminals hood is a lot higher than that of the bonnet insert therefore eliminating tar and creosote build-up and also allows the chimney sweep total access to go through the system and he is able to keep it totally clear with regular sweeping. The chimney pot directional terminal DFE if installed correctly also helps to reduce the ingress of the elements such as rain and snow which can cause problems to the chimney flue itself. In picture (3) you will see what we mean by the tar /creosote build-up in the bonnet insert terminal
In our next blog will be continuing with some more terminals and then going onto cowls and bird guards.
Clive at Clive Scott Chimney Sweeps