|
Everyone enjoys the warmth and ambiance of a crackling fire during the cold winter chills. However, when the fire escapes the compartment in which it is supposed to be contained, it no longer holds its romantic appeal. Fires caused by supplemental wood heating units are one of the major fire problems we experience at the St. Peters Fire Protection District. There are several types of wood heating appliances in use. Types of Woodburning Appliances First, and most common, is the open face fireplace. The fireplace usually has the firebox visible with either glass doors or a mesh screen over the opening. There is usually little control over the amount of air flowing into these units. Another common type is the woodburning stove. This is some sort of metal box with tight sealing doors and dampers in which the air flow to the fire can be controlled. This unit is usually found in living rooms and family rooms or other living spaces. The woodburning furnace is not as popular but there are still many in use. This is a device similar to the woodburning stove but it hooks up to your home's regular furnace and ductwork to distribute the heat. These are usually installed in the basement adjacent to the furnace. Typical Installations The typical construction/installation of most fireplaces consists of a double wall firebox venting into a double or triple wall Class A flue. For the sake of appearance, the flue is usually surrounded by a chase constructed of studs and exterior covering. Woodburning stoves may have a similar chase around the flue pipe, but the stove is left in the open. Some flues and fireplaces consist of all masonry construction. Sometimes just the flue is masonry and the woodburning appliance is vented into it. There are many combinations of construction. During the installation process, extreme care must be given to following the instructions. Proper fit and compatibility of all components must be maintained. Building and fire codes, as well as manufacturer's recommendations must be followed. It is best if such a project is left to the professionals for installation, either during the original construction of the house or later remodeling. A mistake could be very dangerous. The proper permits and inspections during the installation must be obtained. Fire Dangers Keeping and maintaining a woodburning appliance in your home is like keeping any other dangerous item. The safety is in how you install it, Use it, maintain it and respect it. Some of the common problems with these devices are detailed here. - Burning wood in open face fireplaces has been known to "pop" embers outward onto combustibles, such as carpeting. Be certain to have some protective doors or a screen to deflect the flying embers. A proper installation will also have a sufficient non-combustible hearth area to catch them.
- The heat of a fire can radiate through the air with sufficient energy to start a fire if a combustible item is too close. Generally, combustibles should be no nearer than 36 inches, but the further away the better.
- Improper clearances during installation can cause, through the heat of usage over the course of years, the ignition temperature of the surrounding wood structures to reduce through a process known as "pyrolysis." The wood can eventually ignite at an unusually low temperature, in a hidden space behind your wall or in the flue chase. You won't know it until the fire breaks out.
- Bird nests in the flue can ignite and extend to your house. In the spring, birds build nests up in high places; trees, utility poles, houses and, of course, chimney flues. The eggs hatch and the birds abandon the nest through the summer. During the first cold snap in the fall, everyone lights up the first fire of the season. If the flue has not been checked, a hot ember can be carried up the thermal column in the flue and land in the flammable nesting material. The burning nest can either burn out harmlessly or fall onto your roof or into the combustible chase, or through an opening in your attic, causing a major fire. The solution is to have the flue checked prior to the first fire of the season.
- Creosote is an oily substance found in wood. It is found in abundance in freshly cut wood. That is why it is recommended to age the wood for about a year or so before burning it. In a hot burning fire, the creosote oil is burned more readily and the oily vapors rise out of the firebox on the thermal column. If you have a woodburning stove, the type with dampers that can be turned way down for minimal air flow which is good for those "all night burns," this creosote problem becomes most prevelant. Typically, with a well damped fire, the flue gasses are very "cool" by comparison. Therefore, the flue doesn't get as hot. The oily creosote vapors condense on the inside of the flue pipe, much like water vapor condenses on a cool glass of iced tea on a humid summer Day. Those vapors then build up heavy creosote deposits which can burn with great intensity.
With woodburning stoves normally having very low flue gas temperatures and thus the high creosote buildup, they must be maintained on a more frequent basis than fireplaces. Typically, the flue should be cleaned and checked monthly, although how often depends on the frequency of use and how hot the flue gasses are kept. A rule of thumb is that it should be attended to after every cord of wood burned, or monthly. Any time the creosote builds up to about 1/8 to 1/4 inch it should be cleaned. A creosote flue fire is unmistakable and frightening. It rumbles and roars as the very hot flue fire demands lots of air. The vent pipe may glow a dull red. Flames may shoot from the chimney on top of your roof, much like an afterburner on a jet. If this happens, immediately close the firebox and dampers to suffocate the fire. Get out of the house immediately and call the fire department. Do not become complacent with your woodburning appliance. If not properly cared for, it can become dangerous.
|
