Chimneys Are Made to Protect You
A chimney is a structure made of masonry or metal, which surrounds and supports a flue or multiple flues that vent products of combustion from gas, oil, or solid fuel appliances or fireplaces. The flue, then, is the inner part of the chimney, the part that actually contains and vents the products of combustion. Flues can be made of clay tile, as in the case of most masonry chimneys, or of metal, as in the case of prefabricated or manufactured chimneys.
Think of a chimney and the flue within it as a structure built to protect you. That is an important function of all chimneys no matter what kind of appliance or fireplace they serve.
Again, the main purpose of a chimney is to vent the products of combustion from your home. That function is crucial because the products of combustion contain hazardous and noxious gasses. One of the hazardous gasses your chimney needs to remove from your home is carbon monoxide.
Carbon monoxide is a colorless, odorless, tasteless gas that can cause serious illness or death when it is present in sufficient amounts. It is responsible for hundreds of deaths and countless illnesses every year in homes across America. In many cases carbon monoxide in the home originates in a furnace or other burning appliance and finds its way into the house due to inadequate venting.
What causes inadequate venting? There are several possibilities. One is that the flue has become blocked. The blockage can come from debris falling into the chimney due to a deteriorating masonry chimney, or, it may be the result of nests built there by animals or birds. Carbon monoxide can also seep into the house through cracks or holes in flues and chimneys that moisture, chemical residue, or chimney fires have created.
The other important function of chimneys, especially those serving solid fuel burning appliances like wood stoves or fireplaces, is to keep excessive heat from combustible materials that surround the chimney. Heat or flames from a chimney fire can escape through cracks in the clay flue liner or through damaged or missing mortar joints of a chimney. They can then ignite surrounding combustible framing members of a house.
Chimney fires occur within the structure of the chimney itself. They happen when hot flue gasses or cinders ignite creosote accumulated on the walls of an unclean chimney flue. Creosote is a natural byproduct of burning wood. It is highly flammable and will accumulate on the inner walls of the flue under certain burning conditions.
Even without the occurrence of a chimney fire, framing members surrounding a chimney can have their molecular structure altered and become more flammable when exposed to excessive heat over long periods of time. This process is known as pyrolasis. Once wood is sufficiently pyrolized it can ignite at relatively low temperatures and becomes a significant fire hazard.
So, you see, a well structured chimney and flue are designed to offer protection to your family and home from both the dangers of noxious gasses such as Carbon Monoxide, and from the high levels of heat present in the flue gasses of solid fuel burning appliances and fireplaces. But, like all structures, they must receive regular inspections and maintenance in order to maintain their integrity and to continue doing their job.
How To Maintain a Properly Functioning Chimney
It is easy to understand from the information above why it is strongly recommended that all flues and chimneys in use should receive annual inspections and cleaning if neccessary. In fact, you may want to consider more frequent inspections for chimneys and flues that receive heavy use, especially those venting hotter flue gasses that contain creosote and soot produced by solid fuel burning (meaning wood or coal) fires.
A proper inspection of your chimney by a qualified chimney professional should include a thorough examination of the external structure to look for signs of deterioration or weakness. Exterior staining due to flue gasses seeping through the chimney structure, broken or spalled bricks, and deterioration of mortar joints are all signs that your chimney may need repair.
A proper evaluation should also include a visual inspection of the flue inside the chimney. Ideally, that internal inspection should be done with a video inspection device - a special camera lowered down the flue. Such devices allow chimney professionals to detect even small cracks in the chimney liner that may not be seen by the naked eye. According to the National Fire Protection Agency code, cracked chimney liners constitute a significant safety hazard and must be replaced.
All connections from the burning appliance to the chimney should also be thoroughly inspected.
If the inspections described above indicate the possibility of a chimney deficiency, then a more thorough inspection of the chimney and the structural members surrounding it may be required.
However, regular annual inspections by a qualified chimney professional should go a long way towards heading off serious chimney problems and the need for expensive repairs.
It is important to note, for an inspection to yield the best results, the flues to be inspected will need to be cleaned first. Otherwise, soot, creosote, or other residue might mask physical problems with the flue or flue liner.
What You Can Do Between Inspections To Keep Your Chimney Operating Properly
Make sure you have working carbon monoxide detectors in your home and check them regularly. They should be located in the sleeping areas of your home and preferably on each floor. Carbon monoxide detectors can alert you to possible problems within the venting systems of your furnace and gas hot water heater and keep you from prolonged exposure to even low levels of carbon monoxide.
When using wood burning appliances avoid banking the fires and closing the dampers in order to prolong burning. Slower, cooler burning wood fires are the primary contributor of creosote accumulation in a flue. Be certain to burn wood that has been properly aged. Burning green wood also contributes to creosote accumulation.
Whenever possible burn your wood fires hot. Hotter flue gasses prevent the condensation of creosote and pass more quickly through the chimney. They are therefore useful in preventing the accumulation of creosote in the flue. (If you are using a wood stove, be sure to have a stove thermometer in place so you can avoid overfiring your stove.)
It is a good idea to treat your firewood with a compound that will help keep creosote from accumulating in your flue. You can ask your chimney professional for his or her recommendation as there are several compounds on the market created for this purpose.
Make periodic visual inspections of the external portions of your chimney and any connections between burning appliances and your flue. Even cursory visual inspections can alert you to problems like connectors that have come loose or a chimney that is deteriorating.
By having your chimney inspected by a qualified professional on a regular basis and following the simple principles for proper operation of your burning appliances, you should enjoy years of trouble-free operation of your chimneys and flues.