Chimneys are a home feature with a long and practical history. A chimney is a ventilation structure that is designed of clay, masonry or metal. Its purpose is to direct the toxic smoke and/or gases that are produced by a fireplace, stove, incinerator, furnace or boiler away from the areas where people live and work. An architectural structure, chimneys tend to be vertical — or nearly vertical — in order to allow the smoke and gases to flow unimpeded.

Two Primary Types of Chimneys

In spite of how different chimneys can look compared to one another, they tend to fall into one of two categories: traditional masonry or prefabricated.

  • Traditional masonry chimney

A traditional masonry chimney is made of either stone or brick. It typically consists of three parts: the firebox, flue and crown. The firebox is where the wood burns while the flue is the air shaft that leads from the firebox to the roof.

This type of chimney usually features a crown at its top. Its purpose is to both prevent damage from the elements like water and to deter animals like squirrels and birds from gaining entrance to the chimney‘s flue.

  • Prefabricated chimney

A prefabricated chimney consists of a cap and a firebox like a traditional chimney, but its ventilation system is different. Instead of the toxic gasses and smoke exiting the firebox through the flue, they are vented using a simple pipe.

What is a Chimney Damper?

Regardless of whether a chimney is a traditional masonry design or prefabricated, all types have a damper. This is a movable metal plate that allows for control of the flow of gasses, heat and smoke from the structure to the outside.

When the damper is in the open position, smoke, gasses and heat are allowed to exit from the house. With the damper closed, the temperature inside is retained. Some examples of when the damper might remain closed are those times in the winter when the fireplace is not being used or during the summer months.

There are two types of dampers that are typically in use in today’s chimneys: a throat damper and a top-sealing damper. Using a handle to operate it, a throat damper is installed above the firebox.

A top-sealing damper, in contrast, is mounted at the flue’s top. A chain that extends down through the chimney itself is used to open and close this type of damper. Because it seals the top of the chimney, a top-sealing damper also keeps unwanted things out like debris, rain and animals.

What is a Chimney or Flue Liner?

A chimney or flue liner is designed to prevent combustible materials and substances from overheating. It is also installed to help improve the chimney‘s resistance to the corrosion that is usually the result of burning wood.

There are three primary types of chimney or flue liners: clay tiles, stainless steel or aluminum and cast-in-place

  • Clay tile flue liner

A flue liner made of clay tiles is the most commonly used type in masonry chimneys. Though they tend to be inexpensive, a clay tile flue liner often cracks due to the intense heat from the fire. When this occurs, these cracks need to be repaired as soon as possible. Their presence means that toxic gasses are able to enter the dwelling.

  • Stainless steel or aluminum flue liner

A flue liner that is designed of either aluminum or stainless steel is a popular choice — particularly for those people who own an older home. This is because this type of chimney liner is able to be easily installed in chimneys even when there is already an existing liner.

  • Cast-in-place flue liner

A cast-in-place flue liner is made of concrete that is resistant to heat. This product is applied to the walls of the existing flue or chimney. Though this type of flue liner is highly effective, because of the labor involved in installing them, it tends to be more expensive than other types of chimney liners.

Why Should an Existing Chimney be Lined?

The chimney is designed to work together with the fireplace to provide a safe, effective and efficient manner of heating a home. Though some states mandate that a flue liner is required, there may be exceptions for existing structures. In addition, there are a number of states that do not require the installation of a chimney liner.

However, there are three key reasons why lining an existing chimney is a wise idea:

1. Reduce further chimney damage

Lining a chimney means that it is receiving a layer of support. Because the combustible materials leave behind byproducts that are caustic, they can result in a chemical reaction. Over time, these chemicals can damage the brick and mortar that hold the chimney together. The result is that the chimney‘s very structural integrity is at stake.

A chimney liner that is made of stainless steel or aluminum, for example, provides a barrier between the chimney materials and the caustic chemicals that can damage them. This helps to protect the chimneyfrom further damage.

2. Ensures safe venting of toxic materials

Carbon monoxide is one of the many toxic substances that are released by a fire. This tasteless, colorless and odorless gas infects the bloodstream and causes symptoms such as confusion, headaches, nausea and dizziness.

Prolonged exposure can lead to brain damage and even death. Each year, more than 400 Americans die as a result of unintentional carbon monoxide poisoning.

Installing a chimney liner helps ensure that poisonous gases are properly vented outside of the home. If a home is older, or the homeowner is unsure if it has a flue liner, it’s a good idea to get the chimneyinspected.

3. Boost chimney efficiency

A flue liner helps improve the chimney‘s efficiency. If it is unable to draw the gasses and smoke through it because it is too large or too small, the chimney will be less efficient. A chimney flue that has holes or other imperfections will also have a difficult time pushing these materials out. Using a flue liner that is the right size allows your chimney to work more efficiently as a conduit for the removal of these harmful substances.

Preventing Chimney Fires

Creosote is a highly-flammable substance that can build up within a chimney‘s flue unless the chimney is cleaned on a regular basis. Because a chimney fire can reach temperatures as high as 2,000 degrees Fahrenheit, they often have the ability to extend outside the chimney itself.

Even though chimneys are built to withstand high temperatures, the structure of the home and the chimney itself can become so damaged by a fire that chimney repair is necessary. In some cases, an entire replacement of the chimney is required in order for it to be safe to operate in the future.

Although a chimney is often not thought of in terms of maintenance, it’s important that homeowners have these structures cleaned and inspected at least annually. Not only will doing so help pinpoint any potential issues that might need to be addressed, but it can also increase efficiency and help prevent a damaging fire. When choosing a company to perform this service, look for one that has proven experience and expertise.