What Makes a Chimney Fire?
Snuggling up to a wood stove or pellet stove at this time of year is so comforting until you start to worry about having a chimney fire. So how can they be prevented? First of all, chimney fires are very preventable because a clean chimney does not catch on fire. The easiest way to have a clean chimney is to have it cleaned annually by a certified chimney specialist or chimney sweep.
Once you have a clean chimney, the next step is to keep it clean. Chimneys become “dirty” when wood products do not burn completely. Products of incomplete combustion include: smoke, water vapor, gases, hydrocarbons, tar and other assorted materials which create a product called creosote. The creosote is a by-product of incomplete combustion. In order to have complete combustion or to burn your fuel cleanly, there are several factors to consider.
In order to burn your fuel completely, whether it is wood or a wood product like pellets, your fire needs a good source of oxygen. Oxygen will increase the intensity of the fire which burns hotter, faster and more completely. Creosote is not produced with a clean burning fire. However, there is a negative side to a hot and fast fire. You need to be certain to contain the fire inside your stove or fireplace. If you want to add oxygen to your wood stove fire to improve the burning process, the easiest way to do this is to leave the door open. Again though, you must also remember the fire needs to be contained and therefore it is highly recommended that you use a screen to cover the door. Screen coverings are always recommended for fireplaces.
Another way to add oxygen to the stove and fire without the risk of leaving the doors open is to keep the air inlet on your wood stove free of any debris. If ashes build up and block the air inlet, the fire will burn slower and cooler resulting with a buildup of incomplete combustion products like creosote and carbon monoxide.
“Seasoned” hard firewood or hardwood pellets burn more completely. It is important to not only use wood that has been cut for months but to have it “seasoned”. Seasoning wood is a phrase that means to ensure its dryness. Wood which has been split open to improve the drying process is more likely to burn cleaner than unsplit or whole pieces of wood. Wood which was cut a year ago is more likely to be drier than wood more recently cut. Wood stored in the sunshine with air circulating around it, is more likely to be drier than wood stacked or piled in a shady damp area.
Hardwood trees make better firewood than soft wood trees. Some hardwood trees are: oak, ash or maple. Softwood trees include pine, poplar and any of the evergreen variety. Birch is a very good fire wood if it is split open, seasoned for 6 months to a year and then burned. If birch is left longer than a year, it has a tenancy to accumulate moisture and deteriorate. This results in less BTU’s or British Thermal Heating units. Hardwoods produce the most BTU’s and are considered the best wood fuel source.
Finally, an important reminder to prevent a chimney fire is to never burn cardboard boxes, trash or other debris in your fireplace or woodstove. These wood products have other chemicals contained within them and the result is more creosote byproducts when they are burned.
In New England, burning wood as a home heating fuel is very common and most people do it very successfully. If you decide you will be burning a wood or a pellet stove, please remember to keep combustibles at least 36 inches away from the stove (or follow the stove’s manufacturers instructions) and dispose of your ashes properly. Ashes should only be stored in metal cans. They should be covered with a metal lid until they are cool. If you have any concerns about your wood stove and its installation, members of Milton Fire-Rescue are willing to complete a wood stove inspection. Unfortunately, only professional chimney sweeps are equipped to inspect your chimneys.
For further information on chimney fires and wood burning, there are multiple websites with more information. Check out NH’s Department of Safety at: http://www.nh.gov/safety/divisions/firesafety/index.html or FEMA’s website: http://www.usfa.fema.gov/downloads/pdf/publications/l-97.pdf
How do you know if you have a chimney fire?
If you ask a homeowner what was happening before they called 911 to report a chimney fire, the typical response is that they heard a roaring sound like a train or low flying airplane. With these types of chimney fires, you may see flames or sparks coming from the chimney. Other signs may include heavy dense smoke or smell within the home. These are serious active fires and getting everyone out of the home is your top priority.
A slower burning chimney fire is not as dramatic but still serious if not extinguished before it becomes an active free burning structure fire. Sometimes a small slow fire happens in the chimney and it puts itself out due to a lack of oxygen or fuel to burn. You will know you once had a chimney fire if you see “puffy or honeycombed creosote” when you have your chimney cleaned. Other signs include: cracked or collapsed flue tiles, a discolored or missing chimney cap, creosote flakes and pieces found on the roof or ground, cracks in the masonry of the chimney or if you see smoke escaping through joints of the chimney. (Cushman Insurance Group, www.cushmaninsure.com, 2015)
If you suspect you have had a chimney fire, you should have your chimney inspected by a reputable chimney sweep company before you burn again. If you fear the cost of hiring an inspection, you may want to consider the expense of losing your home to a structure fire. Chimney fires do not stay just in the chimney if they have the oxygen and fuel that they need. Chimney fires are dangerous and should not be taken lightly. If you suspect you have a chimney fire, call 911. The sooner you call, the quicker it can be determined if you have a problem. A thermal imaging camera will aid the fire department in the location and seriousness of the heat source. There is no fee associated with calling the Milton Fire-Rescue department. Please do not hesitate to call for help or assistance.