Chimney Basics: What Is A Chimney Flue?

Chimney Basics: What Is A Chimney Flue?

Flue Vs Chimney

A flue is the channel inside a chimney that allows the gas from a heating appliance or a fireplace to safely exit the home. A flue is commonly made from terra cotta clay or a stainless steel liner. To safely exhaust the toxic gas out of the home, the terra cotta clay flue must not have any cracks or missing mortar between the joints and a stainless steel liner must not have any holes or large gaps at the pipe seams. There can be multiple flues inside a chimney to allow different appliances to safely exhaust out of the home. Considering this information, the saying that Santa comes down the chimney is incorrect, it is actually the flue!

A chimney is the actual structure that houses the flue which prevents heat transfer from the flue to nearby combustible material. A chimney is commonly constructed from bricks, blocks or stones. When a clay chimney flue is installed in a brick chimney there must be a minimum of a 1/2" clearance from the clay to the interior brick chimney. The space between the flue and the chimney must not be filled with anything. Stainless steel chimney flues can touch the inside walls of the chimney depending on the type of appliance. When installing a stainless steel flue inside a brick chimney, the flue liner must be wrapped with insulation which will make the chimney zero clearance and free to be in contact with nearby combustible material.

What Does A Flue Do?

A chimney flue allows the exhaust gas from a heating appliance or a fireplace to safely exit the chimney. A flue ensures that no carbon monoxide leaks out of the chimney from a heating appliance. Bricks are porous and not a suitable flue. A good flue will not be porous and corrode easily. The flue should run all the way up the chimney and either be directly connected to the heating appliance or properly sealed for a fireplace. A proper size flue will also make sure the heating appliance or a fireplace has a good draft ensuring optimal performance.

Does A Flue Need Maintenance?

The flue must be cleaned and inspected regularly to ensure optimal performance and safety. Creosote is the byproduct of burning wood in a fireplace of a wood stove and will build up on the wall of the flue. It is very important to clean the flue regularly to prevent the creosote from causing a chimney fire. If creosote builds up in the chimney too much, it will cause the flue to be restricted. A restricted flue will cause smoke to roll out of the front of a wood stove or a fireplace. This will make your home very smoky and the odor will be unbearable.

The chimney should also be inspected annually. Old clay flues tend to crack over time from a small chimney fire or from the home settling. A crack in a flue can cause carbon monoxide to leak out the flue and potentially in your home if the chimney also has cracks. Creosote can also be liquid form and leak through flue cracks. Over time this could combust and cause the home to catch fire. A chimney cleaning brush or SootEater is good to have for a fireplace, wood stove or any other heating appliance. A chimney inspection will tell you if your chimney is in good condition or not. You can also run a camera inside the chimney and look for any cracks or missing mortar joints between the flues. If you do have a crack in the flue, then it is time to reline the chimney.

Installing a stainless steel chimney liner in your chimney is the best way to reline a cracked chimney flue. The 316Ti stainless steel liner is an all fuel liner that is great for any heating appliance or fireplace. The stainless steel chimney flue liner is rated for a max temperature of 2100 degree Fahrenheit and can withstand small chimney fires without harming it. The stainless steel flue liners are available in Round, Oval, Rectangle and Square shapes depending on the current size and shape of your chimney. The flue liners are air and water tight to ensure the safety of the heating appliance or the fireplace. The stainless steel flue liner is a lifetime solution for replacing a cracked clay flue tile. Rockford Chimney Supply allows you to customize the chimney liner kit to your needs, providing many shapes and sizes.

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Our 316Ti flexible chimney liner and chimney liner components have passed the rigorous testing at the Underwriters Laboratories with best in class status and are UL Listed. So if you are looking for UL listed chimney liner sold directly to homeowners, then look no further than Rockford Chimney

Customer Testimonials

Back in July you gave me excellent advice re. sizing/purchasing a flue liner for the chimney associated with my wood stove. I'd like to thank you once agai... More

—AE Northfield, MN

A few weeks ago I ordered a chimney liner system for my fireplace insert. Your salesman recommended the liner system plus the insulating blanket. I just wa... More

—AH Happy customer

Just got around to installing my new smooth flexible liner and deluxe terra cotta cap (wow). The quality of your product is second to none. Very pleased an... More

—B.B. from Massachusetts

Thanks so much for the great tech service from Dennis, very knowledgable, friendly and proffessional.Your website is the best, beats your competition by fa... More

—Bill in Knoxville

Sue and Dennis, I received the final part of my order yesterday (the chimney cap that actually fits over the chimney chase). It looks wonderfu... More


Hello, I was shopping for an fireplace insert and called RCS to ask why they were so much cheaper than my local guy, the reply was " we sell thousand of th... More

—Chris, PA.