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Information on Cowls


There are hundreds of cowls on the market, and choosing the correct one for your chimney can be a minefield. Installing an incorrect cowl can restrict the chimney’s efficiency and make it unsafe for use. There are many different functions for a chimney cowl, depending on the type of heating appliance being used. I have included below a list of the types of cowl that I come across most often while I’m out sweeping chimneys. Some are gas cowls, some are solid fuel cowls and others are ventilation only cowls.

Ventilation Only Cowls

The most commonly seen cowl on chimneys that are not being used are ridge cowls. These cowls stop birds nesting in the chimney and rain from entering the flue. This kind of cowl will allow airflow through the chimney in order to prevent the problems with damp that you may experience if you close the top of flue completely. When you cap a chimney completely, you aren’t allowing it to breathe, which can cause a buildup of unwanted moisture.

Builders generally put ridge cowls on all chimneys, even if solid fuel is going to be used in the fireplace. This is usually because they don’t have the information about which cowls are suitable for which kinds of appliance. Installing a ridge cowl for use with solid fuels increases the risk of a chimney fire, which can affect your insurance policy.

The second most commonly seen kind of cowl is a mushroom cowl. This by far the best type to put on a redundant chimney as it is the best watertight cowl available. They allow the chimney to breathe just enough to stop damp problems in the chimney breast, and they will also prevent animals such as birds and squirrels making a home of your chimney.

Bird Guard Cowls

These cowls are usually put on chimneys to stop birds or squirrels nesting in them. There are hundreds on the market at the moment, so my advice is to aim at spending at least £50 on one to ensure that it’s of decent quality. If you feel you need further advice, then please don’t hesitate to ask me by giving me a call or submitting an enquiry form.

Anti Downdraft Cowls

If your chimney is prone to downdraft (sometimes known as blow back), then this is the ideal cowl type for you. Downdraft can be caused by a number of factors:

-The chimney may need sweeping.

-Factors external to the chimney may be causing it (e.g tall trees outside your house).

-Your house may have been built in an area prone to high winds or strong wind direction changes. This often results in the wind hitting the chimney pot and pushing the smoke back down the flue into the property.

There are two types of cowls you can use to prevent downdraft. The first is a static anti downdraft cowl, which will stop wind blowing down the chimney. A second option is a rotary cowl, which spins on the chimney pot to serve the same function

Gas Cowls

When a gas appliance is being used, I would always recommend that a cowl is fitted to the chimney pot in order to stop the birds nesting in the flue. If a bird nests in your chimney and the fire is being used, then the carbon monoxide will not be released out through the roof, and will instead be redirected into the property. This increases the risk of carbon monoxide poisoning. If your chimney does not have a cowl, then you should ensure that you have it swept every year as a preventative measure.

As I have been in the chimney cleaning business in and around Burgess Hill, Horsham, Worthing, Eastbourne, Crawley etc (see “areas covered” for full details), I have seen a great many different types of cowls. If you need any advice on the matter, then please don’t hesitate to ask me.n please don’t hesitate to ask me.