If your house has a brick or block chimney for a fireplace or woodstove, it might be a good idea to check the "Clean Out" for debris. Chimney creosote, as well as leaves, sticks, or even birds can fall down the flue and cause blockage.
Sometimes, if you don't have a chimney cap and screen, birds will fall into the flue and end up down at the bottom. Birds have been known to perch at the top of a chimney flue to keep warm and then, when they are overcome by the fumes, they fall down the chimney.
Investing in a good chimney flue rain cap with a screen can help prevent this from happening. However, creosote will still build up in the chimney from burning solid fuel such as wood. It is a good idea to have your chimney inspected and cleaned yearly by a certified chimney sweep.
Blockage in a chimney can cause deadly exhaust gases to enter the house and even cause fires.