Chimney Backdraft: How to Prevent it in 6 Easy DIY Steps

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Looking at your chimney, you wouldn’t think that a lot of drama is sparked by it. But when there’s a chimney backdraft issue, what seems like a simple part of your home can cause all sorts of stress and worry, especially if the problem doesn’t seem to go away!

Whether this has been happening for a while or is simply something you want to avoid – read on for some expert-advised ways to keep your household healthy, safe, and free from dangerous backdrafts!

What Is Chimney Backdraft and Why Is It So Dangerous?

When air flows down the chimney, it is called a chimney backdraft or downdraft.

Chimneys are designed to create an upward draft to vent out the exhaust gasses produced inside the fireplace. When the draft inside the chimney is reversed, the air moves down into the chimney, causing a lot of problems for homeowners.

One of the main issues of a chimney backdraft is that it brings soot, creosote, ash, and other harmful particles inside your room. These are toxic substances that can cause eye and skin irritation and even lead to various respiratory issues.

A chimney backdraft brings smoke and Carbon Monoxide (CO) with it as well. CO poisoning is a serious issue and should be avoided, as prolonged exposure can cause death. That is why it is essential to install CO detectors to keep yourself and your family safe.

What Causes a Chimney Backdraft?

Various reasons can cause a chimney backdraft, and it is best to consult a certified chimney sweep to find out the cause of fixing it. Here are some of the most common causes of a chimney backdraft:

The Stack Effect

Chimneys work on a simple principle: heat rises.

But in certain conditions, the same principle can cause issues; one such issue is the stack effect.

When the warm air inside a house rises, it creates a higher pressure at the top while a lower pressure is left at the bottom. The fire burning inside your fireplace also uses room air to fulfill its oxygen needs, and this further lowers the air pressure at the bottom (closer to the floor.)

This isn’t a problem if the room has an adequate supply of fresh air. But the lower pressure must be compensated if there’s not enough air.

Since modern homes are airtight, there is no way for the air to enter except for the chimney. So outside air is pulled inside (along with smoke) through the chimney to compensate for the lower pressure. This phenomenon is known as the stack effect.

The stack effect is further worsened if you have other appliances inside your home that are venting out air. Kitchen and bathroom exhaust fans are among the prime examples. Since these appliances vent air out of the house, the pressure is lowered near the floor, and the stack effect increases.

Cold Chimney

If you face a backdraft problem upon igniting a fire inside your fireplace, the most obvious culprit is a cold chimney flue. When the chimney is not in use, the top of the chimney flue (usually made of stainless steel) is colder because of the lower outside temperature.

Since cold air is heavier, it flows downwards and brings smoke and other harmful gasses.

Clogged Chimney

If you’re facing fireplace draft problems, it may be a sign that you need to get your chimney swept by a professional service. If you haven’t had your chimney cleaned in a while, you’ve likely got a clogged chimney that’s causing smoke and back-drafting issues.

Chimney clogging can occur for various reasons, but creosote buildup is the most common. Chimney sweeping will unclog your chimney and eliminate the chimney back-drafting issue. Since creosote is highly flammable, removing creosote will also minimize the possibility of a chimney fire.

Other reasons for chimney clogging include:

  • outside dust
  • debris
  • fallen trees, branches, and leaves
  • small animals such as squirrels or raccoons


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Backdraft in Chimney Warning Signs

To solve any problem, it’s important first to realize that it exists. So if you know the various signs of chimney backdrafting, you can avoid it.

Here are some of the most obvious warning signs of chimney back drafting. If you notice any of these signs, hire a chimney expert to inspect the chimney and resolve the back-drafting issue:

Eye Irritation

Do you sit beside your fireplace, and it irritates your eyes (even when there is no fire burning?) Chimney back-drafting can drag small soot particles inside your room that are not noticeable. These particles can irritate your eyes and even cause various respiratory issues. 


A chimney backdraft brings soot and other combustion materials inside your room. Since these particles are pretty small, they get mixed with dust inside the room. But if the back-drafting issue is persistent, the dark soot particles will start to accumulate on your window panes.

Smoke Alarms Going Off

Back-drafting could be the reason if your smoke alarms or CO detectors seem to go off for no apparent reason. If smoke alarms go off and there appears to be no noticeable smoke or threat, it’s normal for homeowners to shrug it off. But they don’t realize it could be because of small amounts of smoke or CO.

How to Prevent Chimney Backdraft?

A chimney backdraft can bring many issues, including smoke, CO poisoning, and respiratory problems, to name a few. That is why getting it fixed as soon as possible is essential. Here are a few things you can do to prevent chimney backdrafts from occurring:

1. Clean Your Chimney annually 

If no smoke is being exhausted and there is no upward draft inside your chimney, there is a chance that your chimney or fireplace is blocked and can cause smoke to come into your house. In such cases, it’s best to get your chimney swept.

You should clean your chimney regularly, but if the creosote and soot inside your flue are more than 1/8″, it becomes a health and safety risk. In such cases, the NFPA recommends appropriately cleaning and inspecting it before lighting a fire.

Hire a professional chimney sweeping service to inspect and clean your chimney thoroughly. The chimney sweep will also remove creosote, soot, dead animals, and anything blocking your chimney flue.


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2. Increase Chimney Height

It’s possible that your chimney is not designed optimally, or you live in a windy region requiring a taller chimney. In such cases, increasing the height of your chimney solves the back-drafting problem.

For the best possible drafting conditions, your chimney should follow the 3-2-10 rule:

Your chimney needs to be at least 3 ft. taller than its intersection with the roof, and it should also be at least 2 ft. taller than surrounding buildings or trees within 10 ft. of it.

3. Open a Window

If the stack effect is causing chimney back-drafting, open up a window. It helps compensate for the negative pressure created. But if two or more windows are open, the wind crossing the fireplace room could draw a vacuum inside the house. So in such cases, you’d want to close a couple of windows.

4. Exhaust Fans

If you have exhaust fans running inside your kitchen and bathroom, it’s best to shut them off when you want to ignite your fireplace. This helps prevent the exhaust fans from removing the air inside the house and creating negative pressure.

5. Repair Chimney Damper

A broken, wrapped, or damaged damper can hinder proper airflow and cause backdrafting issues. Adjusting your chimney damper can often help. Sometimes, the damper is damaged or wrapped beyond repair due to the heat coming from the fireplace. In such cases, it’s best to replace it.

A top-mount chimney damper is better if you plan on getting a new damper. It provides an airtight seal and doesn’t get wrapped or damaged due to heat because it is installed at the top of your chimney.

6. Chimney Cap Replacement

Chimney cap and spark arrestor clogging is another common cause of chimney backdrafting. Since a chimney cap is installed way up at the top of a chimney, homeowners usually ignore it. Environmental elements, smoke, dust, and debris accumulate over time and clog the cap, restricting the proper flow of air.

To solve this issue, take a cloth and soak it in a detergent or a water/vinegar mixture. Place the soaked cloth over the cap and let it break down the accumulated creosote. Once broken, use a bristle brush to clean off the remnants.

The Takeaway

Chimney backdraft or downdraft is commonly caused by a negative pressure created due to the stack effect. Other reasons include a clogged chimney cap/flue or a wrapped damper. Whatever the reason may be, chimney backdraft is a serious issue and should be prevented to avoid any health risks.

Sometimes the solution is as simple and cheap as cleaning your chimney cap or flue or replacing your chimney damper. Other times it is as expensive as increasing the height of your chimney top.

But before taking any steps, it’s best to consult a chimney expert to resolve the backdraft issue.

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Thomas Green

Thomas has worked in the Chimney & Fireplace field for over 12 years. He is an expert in his trade and loves to help People with their needs. Thomas Write helpful articles so that homeowners can make the most informed decisions about their fireplace and chimney.