Why Does Smoke Blow Back Down a Chimney?

Chimneys are meant to be uncomplicated contraptions! Smoke and noxious gasses go up and away from your house. The only thing that should come down a chimney is Santa Claus. Simple and straightforward, right?

So why is smoke blowing back down your chimney – and what can you do to prevent this from recurring?

Cold Night: Smoky House?

Nothing is more comforting and cozy than a warm fire on a cold day. When chimneys and heating sources are functioning properly, this is exactly what you will enjoy. The simple explanation is that the warm air from the heat source (i.e. the fire in the stove) rises up through the chimney flue. This is called the draft. A good draft pulls smoke and combustion byproducts (e.g. carbon monoxide) up and out of the home while replacing it with cooler air from outside. This creates a cycle that essentially feeds the fire – fire eats oxygen! – while continuing to move smoke and gasses out.

When smoke blows back down the chimney… There is something wrong. You get that smoky effect, which may be fine if you’re into 2000s-era clubs but is not so pleasant in your home. Not only that, it can create a safety and health hazard. If you can smell the smoke, then you are breathing it in – along with carbon monoxide, volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons, and other pollutants and irritants.

Smoke blowing back down the chimney is a risky and potentially very dangerous situation. Why is this happening?

5 Reasons Smoke Blows Back Down a Chimney – and What to Do

1. The Damper Is Closed

The damper controls the airflow to your firebox. While it can take a little experimentation, learning how to operate the damper allows you to control how fast and hot your fire burns. This way, you can optimize how much wood you use and what your ambient temperature is. That said, the damper needs to be wide open when you light a fire. If the damper is closed, it blocks the path smoke and gasses need to exit the chimney. There is nowhere for it to go but back down into your home.

Again, keep your damper completely open when you light a fire and whenever the doors of the stove are open (e.g. when you are putting in more wood). Do not close it completely unless the stove is off and cold. When you want to control temperature and wood burn, you can adjust it to a partially open position.

2. Your Wood is “Green”

Green means your wood hasn’t had a chance to dry properly. Well-seasoned firewood – which has been left to dry for about 12 months to remove virtually all moisture – ensures a good burn. If the wood is green, it may create a thicker, more abundant smoke that your flue may not be able to handle. This will cause “back-puffing,” or smoke coming back down the chimney.

Make sure you purchase well-seasoned wood. You’ll burn less and enjoy a much more consistent, safe heat.

3. You Have a Blockage

Assuming your damper is open when you start a fire or open the doors of your wood burning appliance, smoke blowing back down may mean that your chimney has a blockage. This could be a build up of creosote or a bird’s nest, for example. In either case, smoke and gasses do not have a clear path out of the chimney and will be forced back down. Regular chimney cleaning and maintenance is essential in preventing this problem (and many others!).

4. Your Home Is Too Well Insulated

Who knew that would be a problem! The fact is that today’s houses are much better insulated than those built prior to about the 1970s. Advances such as spray foam insulation, weather sealed windows, and house wrap create very tight homes that are much more efficient. The issue, though, is that there may not be enough makeup air to allow the wood stove/fireplace to draw properly.

Makeup air is the new air that replaces the air that exits through the chimney. It must be balanced so you have neutral indoor air pressure. The point is, your house may be so tight that it isn’t delivering adequate makeup air. To correct this, you could either open a downstairs window… which isn’t appealing in the middle of winter… or install a chimney fan or powered makeup air kit to your HVAC system or exhaust system. Our team is happy to assess the situation and help you find the solution that works for you.

5. The Weather Outside is Frightful

Extreme cold or wind and cross drafting can cause smoke to blow back down your chimney. For example, when it’s frigid and you have a cold, unused flue, it can fill up with high density air that blocks the path smoke needs to travel up the chimney. It is important to preheat your chimney before your first fire of the season. Learn how with our post, “The Right Way to Light a Fire: Surefire Ways to Stay Warm, Cozy, and Safe.”

Strong winds can also cause “dynamic window loading.” Basically, when wind is gusting on one side of the house, it creates a high pressure zone there and a low pressure zone on the other side. Remember, chimneys don’t like unequal pressure! Again, you can open a window on the windy side of your home or install an outside air kit on the negative pressure side.

Ask the Experts

If you are experiencing a smoky house when using your wood-burning appliance, contact the experts. You don’t want to jeopardize the health and wellbeing of your household or put your home at risk. Brick + Ember will discuss your situation, determine the cause(s) of smoke infiltration, and develop a viable strategy to correct the issue.

Don’t wait! Contact Brick + Ember now.