Cowls and Terminals
The terminal or top of your chimney is a very important part of the system. Terminals include things like pots, cowls, birdguards etc, sometimes it is necessary to fit a guard or cowl if the chimney suffers from downdraught or draw problems. A ‘Cowl’ is an anti-downdraught device, which can be used to reduce wind blowing straight down your chimney, or to prevent birds or rain entering.
Downdraught or cold air coming down the chimney can be due to a variety of reasons and will need investigation and sometimes experimentation to find the best solution. It may only occur with a wind in a certain direction, or may be caused by chimney height, terminal position or design, building design, proximity to other structures, chimney temperature, flue insulation, internal building layout and air extractors or due to a local pressure zone.
Most commonly downdraught is caused by a chimney that is either not high enough or where there are high buildings or trees nearby that affect the wind currents around the chimney. A rotary type cowl may solve the problem but only if the problem occurs when it is windy. If the appliance smokes, but only when the wind blows in a certain direction, then a cowl which reduces wind from a certain direction may be the answer.
If there is any chance that smokeless fuel will be used, any guard or terminal must be made of stainless steel for longevity.
Many terminals are not fitted properly and prevent sweeping through the pot or risk being dislodged. They must have secure fittings that clamp to the outside of the pot and be made of materials that will resist weather, corrosion and the knocks from the sweep rotating the brush inside cowl to clean it.
If the chimney has inadequate draught or draw, the options are relining with an appropriate sized liner for the appliance, increasing the chimney length, increasing internal ventilation or installing a chimney fan (last resort).