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Why Do Wood Burning Masonry Chimneys need a Liner?

Chimney LinerIn the 1950s, the number of chimney and house fires in the United States began to significantly decline. One of the leading reasons is that chimney liners or flue liners had become standard in new homes. Chimney liners are an important safety feature for homes with a wood burning fireplace or wood stove. When a chimney liner is in good condition it protects the connecting walls, ceilings and roof from catching fire from overheating or from sparks that might slip through cracks in the masonry. It also helps your chimney to expel combustion materials more effectively.

Chimneys—which act as an exit for smoke, soot and other combustion byproducts—work best when their interior is smooth, straight and warm. A chimney liner covers the rough walls inside your chimney creating a smoother passage to expel combustion byproducts. It also protects the chimney’s masonry from the buildup of soot and creosote (a flammable substance that collects in chimneys). Insulated chimney liners help further by increasing the flue temperature so that a better draft is produced to expels combustion byproducts more quickly.

Today, a chimney liner is usually put in when the chimney is constructed but it can also be installed after construction. If you have a home that was built in the 1940s or earlier, it is likely that your chimney is not lined. It is wise to have a liner put in if you plan to use your chimney. The lifetime of a chimney line depends on the material used. Some can last for many decades without needing to be replaced. It is important to have a professional chimney sweep annually inspect your chimney liner to ensure that it is not damaged or degraded. Damage to your chimney’s liner can put your home at risk.

There are three different kinds of chimney liners that you can choose from if you are constructing a new home or repairing an existing chimney: clay tile liner, cast-in-place liner and metal flue liner. Each one has different benefits.

Clay Tile Liner

Since the early 1900s, clay tile liners have been used in chimneys. They continue to be used today because of their durability. Clay tiles can withstand extremely high temperatures and perform equally well no matter what fuel you prefer to burn. When installed correctly, a clay tile liner can last for up to 50 year.

They are frequently installed when the chimney is constructed because the material costs for clay tile liners are relatively low. The cost of adding a clay tile liner later is significantly higher because it is a labor intensive process especially if your chimney has “off-sets.”  Fixing an existing clay tile liner is equally costly and challenging.

The difficult task of installing or repairing a clay tile liner requires the expertise of a chimney professional. Improperly installing a clay tile liner with spaces or gaps between tiles can affect the draft of your chimney, let in moisture that damages your chimney’s masonry and leave your home at more risk of catching fire. In order to replace a clay tile liner that is damaged, the old liner must be removed by chipping it out with specialized tools. The walls of your chimney may have to be broken at different intervals to take out the old flue lining and install the new one. If your chimney is crooked or has offsets the tiles will need to be specially cut to fit into your flue correctly, adding to the labor costs significantly. For non-standard chimneys that are uniquely shaped, it is best to choose an alternative lining that is more flexible.

Cast-In Place Liner

Cast-In place liners are similar to clay tile liners in that they have an equally long lifetime, are extremely durable and require professional installation. The mortar used for cast-in place liners can withstand harmful gases and extremely high temperatures. It also provides excellent insulation for chimneys which helps fires to burn cleaner, reducing the buildup of creosote. The process for installing a cast-in place liner requires specialized equipment and a thorough understanding of chimney anatomy.

A cast-in place liner is made by pouring mortar down the chimney with a bladder or vibrating bell-shaped pieces that shapes the opening. A novice might accidentally seal up the chimney or not create a wide enough passageway. A cast-in place liner is typically less expensive than installing a new clay tile liner.

This liner is an excellent option for pre-existing chimneys that do not have a liner or have a clay tile liner that’s in disrepair. Since cast-in place liners increase the structural integrity of chimneys in poor condition, they are also the preferred choice for older or historic homes. Installing a cast-in place liner can allow you to continue using a fireplace with damaged masonry and can re-enforce the original chimney of a historic home.

Metal Flue Liner

Metal Flue LinerOf the three kinds of lining, metal flue liners are the most affordable and versatile. They are usually made of stainless steel. Metal liners come in a large variety of shapes and alloys. They are a great option for unlined chimneys and as a replacement liner, especially for non-standard chimneys that are uniquely shaped or have many off-sets.

There are two types of metal liners: rigid and flexible. Rigid liners do not bend. They are suitable for straight chimneys. Flexible liners are bendable, making them perfect for chimneys that usually would be difficult to put a lining in. Another benefit of installing a flexible metal lining is that they allow less creosote and other combustion byproducts to build up. This happens because they expand and contract as the temperatures within the flue changes, knocking off buildup in the process.  Whether you choose a rigid or flexible metal liner, it is wise to insulate it because insulation increases the temperature within your flue which produces a better draft and gets rid of damaging condensation.

Corrosion is a common problem with metal flue liners over time. To help prevent early corrosion, it is important to consult your chimney professional to determine what metal alloy would be the best choice for you depending on your preferred fuel choice. He or she can also let you know what shape and type of liner will be a good fit for your chimney.

Now that you know more about flue liners, you can understand why chimney professionals emphasize the importance of having a chimney liner and getting it regularly inspected. This guide will help you If you are debating the pros and cons of the different kinds of chimney liners. If you have additional questions or would like to have your chimney lining inspected, contact a chimney professional.

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