Throughout history, fire has been crucial to human existence. Primitive people relied on fire to cook their food, keep them warm and provide light. Although we no longer depend on fire in quite the same way, images of children around campfires
and holiday gatherings around an open fireplace abound. Our use of fire has changed over the centuries, so too have fireplaces and heating appliances that contain the fire and make it useful. One thing that has not changed is that the performance of the fireplace remains dependent upon proper construction and effective maintenance.

Annual chimney inspections by a qualified professional are recommended to help prevent chimney fires and carbon monoxide intrusion. This article will provide you with a better understanding of these dangers and the steps that a CSIA Certified Chimney Sweep will take to determine (and address) the root cause of those issues.

PREVENTING CHIMNEY FIRES

At the most basic level, fireplaces and stoves are designed to safely contain
fires, while providing heat for a home, regardless of fuel type. The chimneys
that serve them have the job of expelling the by-products of combustion – the substances produced when fuel burns. These include smoke, water vapor, gases, unburned wood particles, hydrocarbon, tar fog and assorted minerals. As these substances exit the fireplace, wood stove or furnace 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. Whichever form it takes, creosote is highly combustible. If it builds up in sufficient quantities – and the internal
flue temperature is high enough – the result could be a 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 may be restricted by closing the glass doors, failing to open the damper wide enough, and

the lack of sufficient make-up air to move heated smoke up the chimney rapidly (the longer the smoke’s “residence time” in the flue, the more likely is it that creosote will form). A wood stove’s air supply can be limited by closing down the stove damper or air inlets too soon or too much. Burning unseasoned wood – because so much energy is used initially just to drive off the water trapped in the cells of the logs– keeps the resulting smoke cooler than if seasoned wood is used. In the case of wood stoves, overloading the firebox with wood in an attempt to get a longer burn time also contributes to creosote buildup.

HOW CHIMNEY FIRES HURT CHIMNEYS

Masonry Chimneys

When a chimney fire occurs in a masonry chimney – whether the flue is an older, unlined type or 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, thermal shock occurs and

tiles crack and mortar is displaced, which provides a pathway for flames to reach
the combustible wood frame of the house. This event is extremely dangerous. Call 911 immediately.

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. Most tests require the chimney to withstand flue temperatures up to 2100°F – without sustaining damage. Under chimney fire conditions, damage to these systems may still occur. When factory-built metal chimneys are damaged by a chimney fire, they should no longer be used and must be replaced.

SPECIAL EFFECTS ON WOOD STOVES

Wood stoves are made to contain hot fires. The connector pipes that run from the stove to the chimney are another matter. They cannot withstand the high temperatures produced during a chimney fire and can warp, buckle and even separate from the vibrations created by air turbulence during a fire. If damaged by a chimney fire, they must be replaced.

PREVENTING CARBON MONOXIDE INTRUSION

When most homeowners think of fireplaces or furnaces, it is natural that they think solely of wood burning appliances. Considering
the risks involved when gas or oil systems are neglected - and
the benefits that accrue when they are properly maintained - homeowners would do well to have those chimneys checked annually.

In the United States, numerous agencies and organizations now recognize the importance of annual heating system inspection and maintenance in preventing carbon monoxide poisoning. The U.S.

Consumer Product Safety Commission, the U.S. Environmental Protection Agency, the National Fire Protection Association, and the American Lung Association are some of the organizations that now encourage regular maintenance of home heating systems and their chimneys in order to keep carbon monoxide at bay.

A well-tuned furnace or boiler – connected to a venting system or flue that is correctly-sized, structurally-sound, clean and free of blockages – will operate efficiently and produce a warm and comfortable home.

Consumer confidence in the convenience and safety of today’s home heating systems is usually well-placed. The oil and gas heating industries have achieved impressive safety records. Nonetheless, over 200 people across the nation are known to die each year from carbon monoxide poisoning caused by problems in the venting
of toxic gases produced by their home heating systems. This is according to statistics compiled by the U.S. Consumer Product Safety Commission. Other agencies estimate actual numbers at between 2,000 and 4,000.

In addition, around 10,000 cases of carbon monoxide-related “injuries” are diagnosed each year. Because the symptoms of prolonged, low-level carbon monoxide poisoning mimic the symptoms of common winter ailments (headaches, nausea, dizziness, fatigue and even seasonal depression), many cases are not detected until permanent, subtle damage to the brain, heart and other organs and tissues has occurred. The difficulty of diagnosis also means the number of people affected may be even higher.