Proper construction of chimneys and flues is crucial to maintaining the safety of wood-burning fireplaces in homes.
A chimney is the part of a fireplace system that connects the actual opening to the outside. Runs through the chimney and can be in masonry or metal. Often one is made from stacks of round or square terracotta tubes or round metal tubes. The purpose of the chimney is to release smoke and gases from the fire to the outside.
If connected to a freestanding fireplace, the chimney sometimes includes a chimney thimble. This is a tube sleeve, usually of metal, that connects the pipe coming out of the fireplace to the chimney opening. It often has a damping mechanism, usually a piece of metal that fits inside or just below it, which can be opened or closed. The purpose of a damper is to prevent heat loss when a fireplace is not in use. Opening a damper when the fire is burning should allow smoke to rise up the chimney.
The fireplace duct is designed to safely release smoke to the outside.
If smoke starts to fill the room when the fire is lit, instead of going up the chimney, the register should be checked to make sure it is open. If it is, there are other common causes of a fireplace not working properly. One that is easy to fix is a blocked chimney, usually due to a bird’s nest, wasp, or other animal. Having a chimney sweep to remove the nest alleviates the problem. Sometimes a chimney cap is useful to prevent animals from nesting inside a chimney.
Another situation that can create a smoke problem is that the fireplace chimney must be primed or preheated. Sometimes a cold chimney doesn’t draw smoke. To solve this problem, a piece of rolled-up newspaper can be lit and held as far into the chimney as possible, beyond the damper. This may need to be done more than once to heat the air properly. This entire process is known as priming.
Another potential problem in the flue of a fireplace is the buildup of creosote – a sticky tar-like substance – which can build up due to incomplete burning of wood. It is important to regularly clean the chimney flue, which is used frequently, so that creosote does not accumulate inside. If this substance is not removed, it can catch fire, causing a dangerous chimney fire.