What is a Chimney?


Chimney may not be a part of your home you consider very often, but the health and function of your fireplace depend on it. Chimneys are complicated structures with many parts that work together to create a good draft and protect your house.Chimney

The key components of a chimney include flues, dampers, and caps. Getting to know the anatomy of your chimney can help you understand why having it inspected annually before firing up the hearth is so important.

Flues are the chimney’s primary passage for smoke, combustion gases, and heat to exit a fireplace or wood stove. Typically, there is one dedicated flue for each fireplace or wood stove, though sometimes multiple flues are contained within a single chimney stack. Flues may be made of terra cotta clay, concrete, or stainless steel.

Chimney flues are carefully sized to match the capacity and height of the fireplace or wood stove in which they are installed. This is done to ensure that the chimney can effectively vent combustion byproducts and toxic gases away from the home. When a flue is improperly sized, it can cause smoke, fumes, and carbon monoxide to back up into the house. This can be prevented by installing a stainless steel flue liner that creates the ideal size chimney flue for each fireplace or wood stove.

In addition to being the main passage for exhaust, flues provide several other vital functions for your chimney. Chimney flues are also the primary means for distributing fire’s heat throughout your home, as well as serving as an effective smoke and gas barrier to prevent the spread of fire, smoke, and toxic fumes.

Because of the concept that heat rises, smoke and combustion gases are designed to leave a fireplace or wood stove through the flue. However, if the flue is partially or fully blocked by soot and creosote, the smoke and gases can’t be vented properly. This often exposes occupants to dangerous carbon monoxide fumes and can even ignite a chimney fire.

During the winter, frigid temperatures and windy weather can be particularly destructive to chimneys. Rain, sleet, and snow accelerate masonry damage, make it difficult to light a fire, and can restrict or block flues.

During the cold months, homeowners often warm up their homes by lighting a fire in the fireplace or wood stove. This can warm up the air inside the fireplace, but if the damper is left open, it can interfere with a chimney’s ability to vent. When a draft is not present, the flue cannot be heated adequately to expel the combustion gases and smoke, so they instead back up into the fireplace.


Chimney dampers allow homeowners to control the flow of air and smoke. When a damper is closed, it keeps conditioned (warmed or cooled) home air from escaping up the chimney, along with carbon monoxide exhaust and smokiness. When the damper is open, it allows conditioned air to enter the fireplace and aids in starting and controlling fires.

It’s important to remember to close the chimney damper when the fireplace isn’t in use, especially during warm weather when a strong updraft can rob your home of valuable energy-efficient air. Leaving it open can also allow pests, debris, and rain to enter the flue and firebox.

Dampers are the primary mechanism for regulating the chimney’s draft, both while a fire is burning and throughout the summer. Without a working damper, a cold draft can rob your home of conditioned air and force your heating system to work harder. A well-maintained damper can help prevent this energy loss, reducing the amount of money your home wastes on energy costs.

There are two primary types of chimney dampers: throat dampers and top-sealing dampers. Throat dampers are installed in the base of the chimney over the firebox and opened by a handle that lifts a large metal plate to essentially create a door between the flue and the firebox. This plate is held in place with a chain or crank attached to the handle and is typically known as a “poker,” “rotary or “pivot.”

A top-sealing damper, on the other hand, is located inside the chimney cap and operates much like a standard fireplace handle. A steel cable stretches from the mounted handle, through the cap, and up to a spring-loaded door in the flue. This type of damper is superior to the throat style because it’s far easier to access and more convenient. Older top-mounted styles feature a long chain as the handle, while more contemporary versions have black handles you simply push or pull to operate.

Since you can’t see a throat damper from the inside of your home, it can be difficult to determine its position. When in doubt, you can always check it by holding a pair of safety glasses over the damper to see into the flue. Many throat dampers will even make a thud noise when pulled or pushed, confirming their opening or closing position.

Chimney Caps

Chimney caps cover the top of a chimney, sealing off the opening to protect it from the outside elements. They keep water, birds and other wildlife, leaves, twigs, and debris from entering the chimney and home. They also help to block moisture from seeping through the chimney into walls, ceilings, and other structures. This moisture damage is a major cause of chimney problems and may require costly repairs later. Chimney caps are available in a wide variety of styles and sizes, making them ideal for many homes. They are most often made from galvanized steel, aluminum, or stainless steel.

The simplest type of chimney cap has a mesh screen that keeps twigs, branches, leaves, and other debris from falling into the flue and blocking it. This screen is usually rated as either 3/4″ or 5/8″ mesh. The difference refers to the size of the holes in the screening, but it has no effect on how well a particular chimney cap works.

Other types of chimney caps have a special hood that fits over the opening to keep rain, snow, and other outdoor weather conditions from entering the chimney and damaging its interior components. Some of these hoods also have a screened opening that allows smoke, gases, and heat to escape the chimney. This prevents cold air from blowing back through the chimney during the winter and can reduce heating costs by up to 25%.

These caps also prevent downdrafts that can pull toxic combustion fumes from the fireplace and into the living area. They also keep sparks from escaping the chimney and accidentally igniting the roof or other flammable materials around the house.

Buffalo’s unique ecology attracts numerous wild animals, including birds and other critters that love to nest in the dark warmth of a chimney. Chimney caps with a wire-mesh screen can keep squirrels, racoons, and other uninvited guests out of the chimney. The same screen also stops birds from attempting to make their way inside the chimney, where they can build nests that are both messy and hazardous to your health. The hood also helps keep sleet, ice, and snow from entering the chimney, preventing them from destroying the damper and liner.


Chimney relining is an important chimney service that improves your home’s safety and efficiency. A flue liner protects the chimney structure from water damage and provides a smooth, relatively seamless surface for chimneys to vent gases. If your chimney does not have a flue liner, it may leak smoke, carbon monoxide, moisture, and creosote into living areas of the home. Additionally, unlined chimneys can easily spark combustible materials in attics, walls, and ceilings that are adjacent to the fireplace.

In general, a chimney needs to be relined at least once in its life cycle and more frequently as a result of normal wear and tear or water damage. Having your chimney relined is one of the best investments you can make for your home, as it will ensure that the chimney is safe to use and that it is performing at its peak level of functionality.

A relined chimney will also increase the efficiency of your home heating system since less energy is lost through the chimney and more of it can be utilized for heat generation inside the house. In addition, a chimney that is lined with a high-quality clay flue tile liner can last for 50 years or more. However, even a well-built chimney that is regularly inspected and cleaned will eventually deteriorate from age and exposure to water, heat, and combustion byproducts.

Typically, the chimney will need to be relined when the old clay flue tile liner is cracked or damaged. A new chimney liner will provide a smooth surface for the venting of toxic gases and will also protect the structural integrity of the chimney.

Another reason for a chimney reline is when a home owner switches fuel types or installs a different type of wood stove or fireplace insert. This can cause a chimney to be improperly sized, and the chimney will need to be relined to match the new appliance.

There are several options for chimney liners, including stainless steel, a resurfaced clay liner, and cast-in-place liners. The relining procedure can usually be completed with minimal intrusion into the chimney. The choice of a chimney liner will be based on the condition of the existing flue tiles and the size of the flue, as well as the type of appliance being vented.