Chimney fires are caused by buildup of material inside the flue of a chimney. Smoke flowing from the hot firebox of a fireplace into the cooler space of the flue can cause condensation. The moisture from the condensation combined with deposits of unburned material in smoke attach to the sides of the flue as it rises up to leave the chimney. The unburned portions of the wood that float in the smoke and then attach to the walls of the flue are called creosote. Creosote is a substance that can catch fire and burn at remarkably hot temperatures (approximately 2,000 degrees), causing much damage. Statistics suggest that over 22,000 home fires a year are caused by chimney fires.
Creosote builds up when the conditions in the flue of a chimney are too cool, blocked up so not enough air can get in or from burning unseasoned firewood. Unseasoned firewood is damp inside, and moisture is released in the form of smoke from the wood. As it travels up the flue, the smoke combined with the cooler air of the upper flue creates moisture that adheres to the inside of the flue, which can build up and block air flow, or ignite when burning bits of ash fly up the flue. Blocked air flow causes the smoke to stay in the flue longer than necessary, thereby giving the moist smoke time to set on the inside of the flue. Coolness in the flue (not on the top near the outside but in most areas) is a result of over packing the stove or fireplace. This creates condensation and promotes creosote build up.
Fires occurring inside of chimneys made from masonry or factory made cause significant damage. Fires in masonry cause cracking or melting or the mortar which is the substance that holds masonry chimneys together. Fires also cause whatever liner there is inside the chimney to crack and fall apart. Fires in the pre-fabricated chimneys cause buckling and some cracking, and also perhaps loss of rivets. The pre-fabricated chimneys need to be replaced if there is a fire in them, while repair may be able to be made in masonry chimneys.
Types of Fireplaces
Fireplaces are made in many different types. There are traditional fireplaces that are built in to the home right into the wall. These fireplaces have a hearth and a masonry chimney. read more
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