Chimney Caps - Advantages and Benefits of a Cap
Why you need one
It's worth bearing in mind that, though it may not be the most convenient one, the chimney is another entrance to your house. And as such, it's not necessarily the preserve of white bearded scarlet coated present bearers: you could have other visitors including birds, bats and - worst case scenario - burglars. Hence chimney caps and cowls are very useful things. Keeping unwanted visitors out of the chimney is not their only advantage.
They prevent downdraught, i.e. wind blowing back into your house and anything undesirable that might accompany it, such as soot. They also shield the top of the chimney from ice and frost, potentially extending the flue's life. They keep out rain. And there are caps which are specially designed to help evacuate fumes and hot air from the chimney - see below. Full caps are also put on chimneys which are no longer in use, and if you're opening up a fireplace after a period of disuse you'll need to check whether the chimney has been capped.
Whether your chimney needs a cap or not will depend on how it's made and what it's made of. There are many kinds of chimney caps: among the more specialist ones are vacuum caps which create a stronger updraught with a sort of 'wind tunnel' effect (electric versions of these are also made); caps with inbuilt dampers to increase the heat efficiency of your fire and caps which also extend the length of your flue. Metal chimneys usually need caps, but with masonry chimneys it is a matter of judgment. There are standard chimney sizes, but it's also possible to get tailor made caps if your chimney is not a standard size.
For some chimneys, a bird guard is more suitable. This is a sturdy wire cage which doesn't have to come off if the chimney is being swept. They don't guard against downdraught, though. As always, the Solid Fuel Association (www.solidfuel.co.uk) and National Fireplace Association (www.nfa.org.uk) websites are good starting points for finding information about these and other fireplace accessories. www.hearth.com also features detailed information about chimney caps and links to manufacturers.