Wood burning or gas log fireplaces are a common feature in many homes. In the past, fireplaces and wood burning stoves were the only source of heat in the home, whereas today they are primarily used a design feature, which can lead to their operation and maintenance as being an afterthought. Yet today with the rising price of heating oil, natural gas and propane, many residents may be more likely to rely on alternative heat sources like fireplaces and stoves to supplement the heating systems in their homes during the heating season. Flues and vents for other combustion equipment such as boilers, furnaces, and gas or oil-fired hot water heaters should be inspected along with chimneys.
The National Fire Protection Association (NFPA) estimates that chimneys and chimney connectors are the direct cause of nearly 40% of all home heating fires. Failure to clean the chimney is a contributing factor in 64% of these fires. As the use of alternate heat sources grows these figures are likely to rise as well. Clogged chimneys or vents are also a contributing factor in many carbon monoxide poisonings as well.
The two basic purposes of chimneys and vents are to create a draft for proper combustion and to provide a pathway for the safe removal of combustion byproducts to the exterior of the building. Some problems with draft can occur if the chimney is too short or if it is placed in an area where prevailing wind patterns caused by the roof lines of the house hinder the natural draft of the chimney.
Masonry and prefabricated metal chimneys are the most common chimneys used to vent fireplaces in a home. A less common type of chimney is the single wall metal “smokestack” used on some wood stoves.
What are the Hazards?
Chimney fires and accidental carbon monoxide (CO) poisonings are the predominant hazards associated with chimneys and vents.
Burning wood or other solid fuels in a fireplace or stove produces smoke, water vapor, gases and unburned wood particles. If wood is not burned at the proper temperature the combustion byproducts can condense on the sides of the chimney as they cool and form creosote which is a dark, tarry residue. Creosote is a highly combustible material and can ignite in the presence of hot flue gases that will in turn provide the fuel for a chimney fire. Depending on the condition of your chimney, the fire can find its way through cracks in the mortar and gaps in the clay liner and ignite framing around the chimney.
Natural gas and propane are common fuels for fireplaces with gas log sets, which come in blue or yellow flame and vented or unvented configurations. Yellow flame logs require venting while blue flame logs may be approved for use without a venting system. The yellow flame log sets produce a very realistic and attractive fire, and will often be mistaken for a real wood fire. The heat output from a yellow flame log set will be similar to the heat output from a comparable sized wood fire. Yellow flame, often referred to as "vented" gas logs generate soot and carbon which is deposited in the chimney. These deposits require chimney cleaning just like a real wood fireplace does.
Blue flame log sets are designed to provide much more heat output than a yellow flame log set. While the blue flame log sets are generally not as attractive as the yellow flame, they burn hotter and cleaner. A special type of blue flame log is the "unvented" or "vent free" gas log. Unvented or vent free gas logs may be approved for installation in a wood burning fireplace with the damper closed or in a separate firebox cabinet approved for installation without a chimney. There have been some questions raised recently about the effects vent free gas logs may have on the indoor air quality of a home when the logs are burned for prolonged periods.
CO is a combustion byproduct produced through incomplete burning of carbon based fuels such as wood, natural or liquefied petroleum gas or propane. A build up of CO can happen when a fuel burning appliance malfunctions or there is a leak or blockage in the vent for the appliance. A build up of CO within a building can lead to an accidental carbon monoxide poisoning.
Chimney and Vent Inspections
All fireplaces, chimneys and vents should undergo an annual inspection by a certified chimney sweep. The chimney sweep should then perform any needed cleaning, maintenance or repairs based of the inspection results. The NFPA defines three levels of chimney and vent inspections. The circumstances that give rise to the inspection determine the level of inspection required.
Typical masonry fireplace
A Level 1 inspection is the most common and least invasive inspection and involves examination of the readily accessible areas of the chimney, fireplace and flue to look for obstructions and creosote deposits. This inspection will verify that the chimney is suitable for continued service as installed and under the same conditions.
A Level 2 inspection is required whenever there is a change in the fuel or heat producing appliance connected to the chimney or when installing an additional heat producing appliance. This inspection includes all of the elements of a Level 1 inspection but also verifies proper construction and condition of the accessible portions of the chimney and all enclosed flues. It also verifies proper clearance to combustibles in accessible locations.
A Level 3 inspection is the most comprehensive type of chimney inspection. This inspection is only required after a chimney fire has caused damage to the chimney or the building or if all requirements of a Level 1 or 2 inspection cannot be completed due to lack of access to concealed spaces. This level of inspection may involve removal of building and chimney components to gain access to concealed areas.
Signs of Trouble
A loud roar in the chimney, creosote flakes on the ground, roof or gutter, visible cracks in the chimney, smoke escaping through cracks or into the attic are all signs that a chimney fire has happened or may be burning.
CO is undetectable by the senses because it is odorless, tasteless, and colorless. The initial symptoms of CO poisoning will often mimic those of the flu but without the associated fever. Symptoms may include headache, nausea, dizziness, shortness of breath and fatigue. As the concentration of CO increases in an enclosed space, the symptoms of CO poisoning will appear more quickly and a person may loose consciousness sooner.
CO detectors will detect elevated levels of CO and sound an alarm to alert occupants of a potential poisoning risk. Many newer homes are equipped with CO detectors, but the majority of older homes may not have this safety device installed. Every home that has fuel burning appliances, fireplaces or an attached garage should also have CO detectors installed on every level of the home and in a central location outside each sleeping area.
If you discover that their chimney is on fire, or occupants begin to experience the symptoms of CO poisoning you should evacuate the residence and call the fire department. In multi-residential buildings, you should also activate the building fire alarm or take other steps to alert other building residents.
Older, prefabricated fireplaces may require more attention as their useful life is much shorter than a standard masonry fireplace. Most factory built fireplaces are tested and listed as decorative heating appliances and will not withstand the abuse withstood by masonry fireplaces. Although they are tested to UL standards, severe over-firing and chimney fires will often badly damage these units. Regular yearly maintenance and careful monitoring are required to maintain a safe system. Eventually prefabricated systems can wear out and replacement parts may not be found depending on how old the unit is. At this time, replacement would be necessary.
By inspecting your chimneys, vents, and flues annually, you can determine a cleaning program for your combustion equipment and fireplaces. These measures can reduce the chance of a chimney fire or accidental carbon monoxide poisoning.
Resources
National Fire Protection Association
Chimney Safety Institute of America
IMPORTANT NOTICE - The information presented is based on information from sources believed to be reliable, but is not guaranteed and may not be a complete statement of all available data. Any suggested actions recommended herein are based solely upon an analysis of available industry data and our best judgment. You are encouraged to review all of your proposed plans with licensed professionals before implementing them.
