How does my chimney work? Your chimney, explained

Lucky enough to have a working fireplace? Whenever the weather turns brisk and cool, it’s fun to warm up in front of a roaring fire. But have you ever asked yourself – how does my chimney work? Odds are that you haven’t, but you should!

Asking the question: How does my chimney work?

How does my chimney work

Any heat source that burns fuel has a chimney

Chimneys are designed to remove byproduct gases, like carbon dioxide, from the air. We all think of “fireplace” when we hear “chimney,” but any heat source that burns fuel (wood, oil, gas, coal) requires a chimney.

If you have a gas furnace, for example, it has a chimney. That chimney works in the same way as the one on your wood-burning fireplace.

What is the stack effect?

How does your chimney work? It all starts with airflow. As with a roof system, airflow is the cornerstone to a functional chimney.

Warm air – like smoke – should rise up and out of your chimney as part of the stack effect. This is the same principal that allows warm, moist air to escape your attic through ridge vents with the help of eave vents to properly vent your attic space.

In the case of a chimney, this rising warm is called the draft. A functional chimney will have a strong draft that pulls gases and smoke out of the home through the chimney. A poor chimney draft can put out a flame or leave a room full of cold or contaminated air.

The 4 primary factors that affect chimney draft

How does my chimney work

Air pressure is the weight of the atmospheric pressure exerted onto earth. When air pressure in a home is in balance, air is flowing into the home at the same rate that it is flowing out of the home.

Lighter, warmer air is able to rise up and out of your chimney and is replaced by heavier, cooler air. This fresh, cooler air enters your home via tiny gaps around windows, doors, trim, etc.

NOT ALL AIRFLOW IN A HOME IS BAD!

While you may think that these gaps should be sealed, that’s not quite the case. If a home is sealed too tightly, or if too much air is being vented out, then negative air pressure is realized.

  • When the air pressure in a home is negative, a fire may not burn, or a gas furnace may not work properly.
  • On the flip side, too many air leaks in a home can cause the home itself to act like a chimney. Your house will suck warm air up and push it out through the top of your home. This creates energy inefficiency, which you will see in your energy bills!

What if my furnace or fireplace isn’t working right?

If you are asking “how does my chimney work?” it may be because, well, it’s not.

An air pressure issue could be to blame. William B. Hussel, president of The Chimney Doctors, offers an easy way to test for sufficient airflow in your home using an open door or window and your fireplace.

  • If you find that your airflow is insufficient, a fresh air intake can be added. This helps feed your fire with fresh air and corrects air pressure imbalances. Your local chimney sweep company or HVAC pro can help you identify and correct the causes of unbalanced air pressure in your home.
  • An improperly sized flue is one of the most common reasons for chimney dysfunction. The flue is the opening in the chimney that allows the hot gases to escape.The flue is often hidden behind the masonry that surrounds it.Old flues were often made of brick or stone. Today, it’s common to line a flue with metal, clay or ceramic conduit that can withstand the intense heat from burning fuel.These materials prevent heat from transferring to the main structure while their smooth surfaces inhibit the buildup of byproducts—both properties aid in preventing chimney fires.

How does my chimney work

  • Flue liners also increase efficiency and performance. An appropriately-sized flue should be one inch wide for every 10 square inches of fireplace opening. This 10:1 ratio enables air to travel at the perfect velocity through the flue.
  • If the flue is too big for the fireplace, too much air will exit the chimney and you will lose heat. If the flue is too small, then air cannot exit the chimney fast enough and you may find yourself in a smoke-filled room.

Taller chimneys produce a stronger draft

According to Woodheat.org, taller chimneys produce a stronger draft. What does “tall” mean?

  • The chimney should be at least 15 feet tall from the base of the fireplace (or insert) to the top of the chimney.
  • The top of the chimney should extend at least 3 feet beyond the point at which it penetrates the roof.
  • If your chimney is within 10 feet (horizontally) of another building or obstruction, then the height of your chimney should be extended to be at least 2 feet taller than that barrier.

Extending the height of your chimney serves two main purposes:

  1. Wind-induced downdraft is reduced
  2. Minimizes the likelihood of hot sparks or embers landing on rooftop

Creating a sufficient draft

Finally, to create a sufficient draft, your chimney must be free from obstructions and damage.

The tight, safe space of a chimney coupled with the added warmth from your home makes a great place for birds and squirrels to nest and store food.

Bats and chimney swifts favor the dark, vertical space that chimneys provide.

Flotsam or fowl, these obstructions prevent air from flowing out of the chimney and can create a fire hazard.

Fortunately, the solution is affordable: a chimney cap is a great way to prevent foreign objects from jamming up your chimney. They also prevent water from entering and can contain hot sparks that might have otherwise landed on your roof.

Get inspected!

How does my chimney work

Annual chimney inspections are another great way to prevent damage and maintain the safety of your chimney. The CSIA categorizes chimney inspections into 3 different levels. Choose the level that best suits your needs based on the CSIA descriptions.

So know you know the answers in case anyone ever asks you, “how does my chimney work?” And we have one more answer – for the time you realize you need a new roof.

Long Roofing now serves the Charlotte, North Carolina, Harrisburg, Pennsylvania and Richmond, Virginia metro areas.

If you need a roof replacement, you need a roofer that understands every roof is unique. Roof replacement is affected by the objects on your roof like your chimney. We will work with you to put together a roofing package that you can live with – including our 50-year warranty.

We bring trust and peace of mind to every Long Roofing roof. Contact Long Roofing at 1-866-328-1187 or visit us online to get a price, schedule a free, in-home consultation or find answers to any home roofing questions.

Long Fence & Home also provides roofing, windows and doors in the Washington, D.C. metro area.

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