Chimney Pots & Cowls
If you are using your chimney, i.e. you have an open fire or a stove in use, it is essential that your chimney pot and any cowls are fit for purpose. The information below should help you to understand more about the requirements for your chimney pots and cowls.
Chimney Pots and Cowls
Keeping your Chimney Pots and Cowls in good working order is essential to make sure emissions from your fire, like smoke and Carbon Monoxide, can escape your property safely and to make sure the pots and cowls are not at risk of falling off.
There are many types of chimney pots and cowls in all sorts of different shapes and sizes. The general rule for burning solid fuel is that the minimum diameter of a chimney pot opening is 200mm (approx 8 inches). Anything smaller than this is not suitable and any cowl that reduces the opening to below this is also not suitable.
There are a number of cowls that are designed for ventilation only, i.e. they are not for use on working fires. They are some of the cheaper cowls on sale at builders merchants and as such are often put on top of chimney pots that are in use, as the builder or DIY enthusiast is not aware of the dangers.
These cowls restrict the opening of the chimney pot to the extent that emissions from the fire may not be able to escape properly resulting in smoke and Carbon Monoxide coming back into the room.
Examples of cowls that are not to be used on working fires are detailed below in the section called ‘Cowls That Should Not Be Used On Working Fires’. if you have one of these cowls on top of the flue you are using, i.e. the one servicing your fire, you MUST remove it BEFORE using the fire.
Rain caps and anti-downdraught cowls are often used on top of chimney pots and some have wire mesh incorporated into them to stop birds getting in. Where a cowl with mesh is used, the mesh size, i.e. the gap between the mesh wires, must be at least 2cm x 2cm wide to minimise the risk of soot collecting in the mesh and blocking it. Cowls that are designed for gas fires have much smaller mesh or opening sizes and as such soot can easily collect in them and eventually block them.
As always, chimneys that are in use should be swept regularly to remove sort and other debris. If there is a cowl on top, this means the chimney sweep brush will not be able to exit the pot. This is not a problem as long as the brush makes it to the cowl.
Do I Need A Cowl On Top Of My Chimney Pot?
The simple answer is, generally no you don’t. The most important thing to remember is that if you do have one or want one, it MUST be the right type of cowl and there are lots that are not suitable for working fires.
Many people believe that a cowl is required to stop rain from entering the chimney, but most properties in Brighton & Hove don’t have cowls and they are still standing. This is because moisture that falls inside the chimney will evaporate away. However, this does rely on the fact that the other end of the chimney, i.e. the fireplace in your room is open and has not been bricked up.
The flue is the cavity that runs from just above the fireplace, through the chimney breast right to its own dedicated chimney pot. If it is open both ends then air can flow through and this means any moisture that does get in at the top will evaporate away. If it has been completely blocked off, i.e. the fireplace has been completely covered over in some way, then air cannot flow and moisture inside the flue will not evaporate away. instead it will collect, soak into the brickwork inside the flue and eventually cause damp problems.
If you do brick up or close off a fireplace in some way, you MUST leave an air vent in the new wall so some air can still flow.
If you have a stove with a flue lining, you should always have a suitable cowl fitted to stop or minimise moisture from getting in. As the lining is made of steel rather than brick, moisture will run down it and not soak in. The moisture can get all the way to the stove itself and can cause corrosion on the stove and lining.
It is very rare for birds to nest on top of open chimney pots as it is more difficult to build a nest on top of a hole. Most birds nest in amongst chimney pots, on top of the chimney stack. Nesting birds can cause problems by dropping debris down chimney pots. There are some birds however that do nest inside chimneys, most notably Jackdaws. This is more common nearer to the countryside than the seaside.
Cowls That Should Not Be Used On Working Fires
The images below show cowls that are designed for ventilation only, i.e. they are not to be used on working fires. They are some of the cheaper cowls on sale at builders merchants and as such are often put on top of chimney pots that are in use, as the builder or DIY enthusiast is not aware of the dangers.
These cowls restrict the opening of the chimney pot to the extent that emissions from the fire may not be able to escape properly resulting in smoke and Carbon Monoxide coming back into the room. if you have one of these cowls on top of the flue you are using, i.e. the one servicing your fire, you MUST remove it BEFORE using the fire.