What’s a Flue? Learn the basics about Chimney Ventilation

Many of us know nothing about our chimneys or what they do. We all know that it vents smoke and gases to prevent toxins and carbon monoxide from entering into our homes. Did you know that each appliance in your home should have its own separate flue? So let’s just say your home has one wood stove and a gas or oil furnace. This means your chimney should contain two separate flues. A question that we ask every customer when they call is “How many flues are in your chimney?” a majority of people have no idea. “What’s a flue? “ When burning wood, deposits of ash or creosote can build up on the insides of your chimney and potentially cause a clog. A clog will prevent your chimney from venting properly. If you are also venting your oil or gas stove through that same flue, the fumes from your fuel oil cannot escapee and will back up into your home and put you at risk of carbon monoxide poising.

Basic Terms to Know for Chimney Ventilation


CHIMNEY – a vertical channel or pipe that conducts smoke and combustion gases up from a fire or furnace and typically through the roof of a building.

FLUE – (lining in a masonry chimney)- “A clay, ceramic, or metal conduit installed inside of a chimney, intended to contain the combustion products, direct them to the outside atmosphere, and protect the chimney walls from heat and corrosion.” Although building codes vary from one state or locality to another, the installation of flue lining has been recommended since the early part of this century, and indeed most fire codes now mandate liners

CREOSOTE – Anytime a fireplace is used, creosote is deposited in the chimney lining or flue. Since creosote is highly flammable and probably creates the biggest potential hazard when using a fireplace, it’s wise to try and minimize the amount of buildup that occurs. Failure to remove creosote from the flue can result in a deadly chimney fire, according to the National Fire Protection Association.

CARBON MONOXIDE – (CO) is an odorless, colorless gas often formed in the process of incomplete combustion of organic substances, including fuels. It is dangerous because it interferes with normal oxygen uptake for humans and other living organisms needing oxygen to live.

CO is a gas that can build up to dangerous concentrations indoors when fuel- burning devices are not properly vented, operated, or maintained. Because it has no odor, color or taste, CO cannot be detected by our senses. It is estimated that unintentional CO exposure accounts for an estimated 500 deaths in the United States each year. Poisoning contributes annually to more than 2,000 deaths in the United States. In addition, the US Consumer Product Safety Commission estimates that 8,000 to 15,000 people each year are examined or treated in hospitals for non-fire related CO poisoning. Breathed over long periods of time, low concentrations of CO may also contribute to other illness. Fortunately, simple measures can be taken to prevent CO problems. One such action is the installation of a CO alarm to detect potentially deadly conditions.

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