Chimneys & Fireplace                                  

            

Creosote and Chimney Fires

  • Wood burning fireplaces and wood stoves are designed to safely contain wood-fueled fires while providing a comfortable setting and in some cases heat for a home. The chimneys that serve them have the job of expelling the by-products of combustion — the substances given off when wood burns.

  • As these substances exit the fireplace or wood stove, and flow up into the relatively cooler chimney, condensation occurs. The resulting residue that sticks to the inner walls of the chimney is called creosote. Creosote is black or brown in appearance. It can be crusty and flaky … tar-like, drippy and sticky … or shiny and hardened. Often, all forms will occur in one chimney system.

  • Whatever form it takes, creosote is highly combustible. If it builds up in sufficient quantities — and catches fire inside the chimney flue — the result will be a chimney fire. Although any amount of creosote can burn, sweeps are concerned when creosote builds up in sufficient quantities to sustain a long, hot, destructive chimney fire.

  • Certain conditions encourage the buildup of creosote, restricted air supply, unseasoned wood and cooler-than-normal chimney temperatures are all factors that can accelerate the buildup of creosote on chimney flue walls.     

Air supply

  • The air supply on fireplaces may be restricted by closed glass doors when there is no external air source such as a vent, usually seen in the back or on the side of the firebox, or by failure to open the damper wide enough to move heated smoke up the chimney rapidly (the longer the smoke’s “residence time” in the flue, the more likely it is that creosote will form). A wood stove’s air supply can be limited by closing down the stove damper or air inlets too soon and too much, and by improperly using the stovepipe damper to restrict air movement.                               

Burning unseasoned firewood

  • Because so much energy is used initially just to drive off the water trapped in the cells of the logs – burning green wood keeps the resulting smoke cooler as it moves through the system, than if dried, seasoned wood is used.         

Cool flue temperatures

  • In the case of wood stoves, fully-packed loads of wood (that give large cool fires and eight or 10 hour burn times) contribute to creosote buildup. Condensation of the unburned by-products of combustion also occurs more rapidly in an exterior chimney, for example, than in a chimney that runs through the center of a house and exposes only the upper reaches of the flue to the elements.                                                                                                                        

How Chimney Fires Damage Chimneys

Masonry chimneys

  • When chimney fires occur in masonry chimneys – whether the flues are an older, unlined type or are tile lined to meet current safety codes – the high temperatures at which they burn (around 2000′ F) can “melt” mortar, crack tiles, cause liners to collapse and damage the outer masonry material. Most often, tiles crack and mortar is displaced, which provides a pathway for flames to reach the combustible wood frame of the house. One chimney fire may not harm a home. A second can burn it down. Enough heat can also conduct through a perfectly sound chimney to ignite nearby combustibles.                                                                                                                                                          

Pre-fabricated, factory-built, metal chimneys

  • To be installed in most jurisdictions in the United States, factory-built, metal chimneys that are designed to vent wood burning stoves or pre- fabricated metal fireplaces must pass special tests determined by Underwriter’s Laboratories (U.L.). Under chimney fire conditions, damage to these systems still may occur, usually in the form of buckled or warped seams and joints on the inner liner. When pre-fabricated, factory-built metal chimneys are damaged by a chimney fire, they should no longer be used and must be replaced.                                                                              

Ways to Avoid Chimney Fires

Chimney fires don’t have to happen. Here are some ways to avoid them

  • Use seasoned woods only (dryness is more important than hard wood versus soft wood considerations)bullet Build smaller, hotter fires that burn more completely and produce less smoke.

  • Never burn cardboard boxes, wrapping paper, trash or Christmas trees; these can spark a chimney fire.

  • Install stovepipe thermometers to help monitor flue temperatures where wood stoves are in use, so you can adjust burning practices as needed.

  • Have the chimney inspected and cleaned on a regular basis                                                                                                                         

Chimney Cleaning

How the chimney is cleaned

  • Brushes are used to remove creosote and soot from the firebox, smoke shelf, elbows, and connector pipes. This is done from both outside and inside the house. Occasionally there is creosote buildup that cannot be removed by brushing. Professional chimney sweeps use chemicals to alter the composition of the hardened creosote and turn it into a powdery substance that can be easily removed.                                                                                                               

Chemical vs. mechanical cleaning

  • Chemical chimney cleaning products are available for use by homeowners. The Chimney Safety Institute of America (CSIA) cautions against using these products to replace professional, mechanical cleaning of the chimney. Homeowners should be aware that these products can loosen debris that can fall into hard to reach places in the chimney structure and cause malfunctioning of the chimney. In addition, professional inspection is important because it often reveals hidden problems with the structure of a chimney that would otherwise go unnoticed, and could be potentially hazardous.                                                                                                                                                            

Certification

  • Chimney sweeps can receive national certification through the Chimney Safety Institute of America. In addition, they can be certified at the state level.                                                                                                                                                                  

Chimney repair

A properly functioning chimney has enough draft to pull smoke out of your home and provide enough oxygen for hot, complete burning of wood to occur. It is important that your chimney is the right type and style for your firebox or stove. In addition, it should be installed properly in your home in compliance with building codes and manufacturer instructions. A well-designed system has the following performance characteristics:

  • Fires light easily and burn bright and hot.bullet draft builds quickly.

  • Lighting fires does not cause smoke to fill room.

  • Opening the door does not cause smoke to spill out.

  • When fire is not in use, air flows into the stove and cold air and bad smells do not come out.                                         

Common repairs

The purpose of your chimney is two-fold. It must remove harmful byproducts created when fuel is burned, and it must carry excessive heat away from combustible items near the fire. Besides being cleaned and inspected each year, your chimney will also need occasional repairs to ensure that it is performing these functions properly. Repair work can be done by masons or fireplace professionals.

  • Firebox re-pointing and rebuilding – The firebox is the brick area where you build your fire; loose bricks and degraded mortar should be repaired.

  • Mortar crown repair – The mortar crown is the concrete like surface at the top of your chimney that keeps water out of your flue; a cracked or broken mortar crown should be repaired immediately to avoid serious water damage.

  • Damper repair – A damper closes the flue when you aren’t using the fireplace so heat doesn’t escape through the chimney.

  • Flue repair – The flu is the internal part of the chimney that funnels exhaust from your fireplace to the outside, if it cracks, breaks, or is blocked by debris or creosote build up it is a safety hazard that needs to be repaired.                

Rain Caps

Rain caps with wire mesh around them (spark arrestor) should be installed over the flue to prevent rain water and snow from directly entering the chimney and to keep rodents and birds out.                                                                                                       

A note on carbon monoxide

  • A chimney functions to remove the byproducts of burning fuel. Carbon monoxide is one of these byproducts. It is a colorless, odorless gas that is a serious health hazard. It causes illness and death if it is inhaled in large amounts. For the safety of your family and guests is critical to that your chimney is maintained properly so that carbon monoxide and other harmful fuel byproducts do not enter your home. Annual inspections are important. Also, you should have carbon monoxide detectors installed on each floor of your home, as well as in sleeping areas. Carbon monoxide detectors can let you know if there are possible problems with the venting systems of your furnace, gas hot water heater, or gas stove and will keep you from being harmed from prolonged exposure to low levels of carbon monoxide.                                                                                                                                                                                                                    

Other safety tips

  • Do not bank fires or close dampers to prolong burning.

  • Burn properly aged wood, not green wood.

  • Burn fires hot to minimize creosote buildup.

  • Regularly check the outside parts of your chimney and any connection points for any visible damage.

  • Have your chimney cleaned and inspected annually by a professional.

For more information or to find a Certified Chimney Sweep visit the Chimney Safety Institute of America

Also visit the National Fire Protection Association.                                                                                                                                                                                                

                         Maintenance note                                   

  •  If you use your fireplace regularly, it’s advisable to hire a chimney-sweep  to clean the fireplace and chimney once per year. Debris that builds up inside the chimney can create a serious fire hazard.

  • The safety guidelines set by the National Fire Protection Association call for annual professional inspections of all wood and coal stoves, fireplaces, chimneys, chimney connectors, and all other solid-fueled heating equipment. Follow up cleaning should be done according to inspection results.     

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