Why Is My Fireplace Smoking?

A smoky fireplace can be a serious inconvenience. The moment smoke starts pouring back into your home, the enjoyment of the evening is gone. You go from relaxing and sipping your favorite beverage to opening windows and trying to figure out what the heck is going on.

Smoke can stain your furniture, drapes, and walls, cause coughing fits and respiratory problems, and – because it contains carbon monoxide – it can make you sick. Of course, when you’re waving away the smoke, you’re not thinking about all that. You’re thinking ‘something’s wrong’ and wondering why you can’t just have a relaxing night by the fire. 😒

Well, you’re right: Something is wrong. It’s not normal for your fireplace to push smoke back into your home. But we can help you figure out what might be going on, so you can fix the problem and once again enjoy the relaxing warmth you hoped your fireplace would provide.

Let’s go over some of the most common causes of a smoky fireplace and what can be done about each.

#1 You’re burning green/wet wood.

Your fireplace is designed to burn dry, properly seasoned wood – wood with a moisture content somewhere between 15 and 25%. Wet or green wood that hasn’t been seasoned will have a moisture content around 40-50%, and that moisture will naturally produce more smoke.

The reason is that when you burn wet wood:

  • Any BTUs produced by the fire will be used to dry the wood.
  • The fire will burn cooler and produce more smoke.
  • The flue gases will be cooler and the flue won’t be adequately warmed.
  • The chimney won’t be able to swiftly move all the smoke up and out of the chimney.

Voila: Smoke problems.

So, how do you know if your firewood has the right moisture content before you use it? The easiest way is to check your firewood using a moisture meter. Many hardware and big box stores carry them, and Amazon, of course, has everything.

Simply split the firewood and use your moisture meter to get a reading. If it’s somewhere between 15 and 25%, you’re good. If not, you’ll need to season the wood or buy your firewood somewhere else.

Check out this quick video for more info + tips on storing firewood.

Want even more? You’ll find everything you need to know about buying, seasoning, and storing firewood in our Ultimate Guide to Firewood right here.

#2 You haven’t properly warmed the flue.

You’ve doubtless heard that hot air rises – well the chimney needs a bit of heat to pull the smoke produced by your fireplace up and out of the chimney. The hotter the flue, the faster the byproducts of combustion (like smoke) can move through it.

The problem is, if the outside air is much cooler than the air in the home, the chimney flue may be cold when you first light a fire. This is especially common with exterior chimneys that don’t have the warmth of the home on every side.

One thing you can do if you have an exterior chimney or think a cold flue may be the problem is prep the flue. You can do this by taking a rolled-up newspaper, lighting the end, and holding it up into the chimney prior to lighting your fire in the fireplace.

Another great way to heat the flue naturally is to build a top-down fire. With a top-down fire, you’re lighting the small bits of tinder and kindle at the top first. Those small bits will burn hotter, and they’ll be closer to the flue – which makes it easy for them to warm the flue before your fire really gets going.

For more info on how to build a top-down fire, including a step-by-step guide and a video explanation, check out The Ultimate Guide to Using Your Fireplace.

Lastly, if you have an exterior chimney, you may want to invest in a top-sealing damper. Traditional dampers are installed down in the throat of the chimney, just above the fireplace. And while they prevent cold air from coming into the home through the fireplace opening, they offer no protection to the flue. A top-sealing damper, on the other hand, protects the chimney and keeps the flue warmer by sealing the chimney up at the top.

#3 You’ve built a fire that’s too big for your fireplace.

Bigger is better, right? Well, not always. In fact, if the fire you’ve built is too big for your fireplace, you won’t have a better fireside experience. You’ll have a lot of smoke.

This is because, if the fire is too big for the fireplace, the chimney won’t be able to move all the byproducts of combustion (including smoke) up and out of the home fast enough.

It’s like when there’s a rush of people trying to get through the same small door – the door can’t accommodate all those people and it wasn’t made to. So, everyone gets held up at the exit. But when the smoke in your chimney and fireplace gets held up, it flows back into the home and cools in the chimney as creosote. Both are bad news.

How big should your fire be? Well, naturally, it depends on your fireplace. But there are some general rules to keep in mind, no matter the size of your fireplace. For example:

  • There should be space between the logs and the walls of your fireplace.
  • Your logs, tinder, and kindle should not extend up past the fireplace opening.
  • You should be able to see the tips of the flames in your fireplace opening once you get the fire going.

If you stick to these general rules, you should be in good shape.

#4 Your chimney liner is the wrong size for your appliance.

If you’ve had smoke problems ever since you relined your chimney or installed a new fireplace or insert, there’s a good chance there’s a sizing issue. We won’t bore you but there’s a magic ratio for determining liner size for each appliance.

If the math was wrong when you had a new liner or appliance installed and the flue liner is too small for the appliance, you’ll have smoke problems. This is because the appliance is producing more smoke and byproducts than the liner can manage to quickly move through the chimney.

The best thing to do is to have a CSIA-Certified Chimney Sweep® evaluate your liner and appliance. They can check for a mismatch and other installation issues and recommend a resolution (like a reline or a smoke guard). Easily find one in your area right here.

#5 You have a chimney blockage.

You’d be surprised what chimney sweeps find in chimneys. Squirrels, birds, raccoons, broken flue tiles, and chunks of creosote are just a few examples. The trouble is that all these can cause dangerous blockages that prevent carbon monoxide and smoke from swiftly exiting the chimney top. That’s why you end up with smoke pouring back into your home.

The best thing to do if you suspect a chimney blockage is to schedule an inspection with a CSIA-Certified Chimney Sweep® and have your chimney cleaned if they confirm a blockage or buildup.

Dirty chimneys and blockages don’t just cause smoke issues – they can also cause chimney fires. So, don’t use your chimney system until the problem’s taken care of.

#6 Your chimney isn’t tall enough to achieve good draft.

Another common cause of smoky fireplaces is an issue with chimney height. To achieve proper draft, your chimney needs to be a specific height, and it should be the highest thing in the vicinity – meaning no other part of the home should be as tall as it is.

If chimney height is behind your smoky fireplace problem, you may be able to resolve the issue by extending the chimney. The added length typically improves draft and increases the pull of air up the chimney, which gets smoke up and out faster.

An experienced chimney sweep should be able to tell if chimney height is the cause of your smoke problems. Find a qualified pro to inspect your system right here.

#7 Stack effect.

When warm air rises to the upper areas of your home, it’s called the stack effect. That trapped air forces its way out – even through very small openings, such as recessed light fixtures and window frames. To make up for that escaping air, replacement air tries to enter in the lower part of the building.

Somewhere in your home, amid all this airflow, is what’s called the Neutral Pressure Plane (NPP). Above this theoretical plane, the air pressure is slightly greater than the outdoor air pressure, and so the inside air tries to force its way out of the house. Below this plane, the air pressure is slightly negative, and the house attempts to draw air in from the outside.

Diagram illustrating the stack effect in a house

Anytime a fireplace or fuel-fired heating appliance (except direct vent) is below the Neutral Pressure Plane, you tend to have smoky fireplace problems.

A common example of this is found in homes with two fireplaces, one below the other. As the upper-level fireplace uses air for combustion and chimney flow, it depressurizes that level slightly, causing air to flow upwards from the lower level. Since the lower-level fireplace is below the Neutral Pressure Plane, it draws air in to replace that air through the chimney.

Typically, the flues for both the upper- and lower-level fireplace exit the chimney close to each other, so the replacement air being pulled into the lower-level chimney often contains some smoke from the fireplace above – hence why you find smoke coming in through your unused fireplace.

If this is the cause of your smoky fireplace, the solution may be to install a top-sealing damper on the lower fireplace flue and keep it closed when the other fireplace is in use.

#8 Wind-loading

Wind-loading is the effect on interior house pressures caused by the wind. When wind strikes a building, it creates high pressure on the side it hits and low pressure on the downwind side. Any open windows or doors on the windward side will help to pressurize the house, increasing chimney draft. But openings on the downwind side (even small openings in the home) will depressurize the house and increase the likelihood of backdrafting in chimneys and vents. Backdrafting is a reversal of airflow in which smoke comes into the house instead of going up the chimney.

If this is the cause of your smoke issues, you may need to install a specialty chimney cap made for high-wind areas. These types of caps work by using the wind to create a partial vacuum. This prevents downdrafts and backdrafting, improving draft and pulling smoke and other byproducts of combustion up and out of the home.

#9 Competing interior mechanical devices

Clothes dryers, kitchen fans, bathroom fans, attic fans, and central vacuums can all create depressurization by removing large volumes of air from the house. This often creates negative pressure in the area of a fireplace, woodstove, or other fuel-fired heating appliance, which makes it difficult for natural draft chimneys to function as intended. As a result, smoke may flow back into your home through your fireplace opening.

Another appliance that can cause smoke issues is the forced-air furnace. These appliances need large volumes of combustion air, just like fireplaces and woodstoves. Unless they are especially equipped to draw air in from outside the house (like direct vent fireplaces, which have both an air intake and an exhaust pipe), operating them can reduce the inside air pressure and cause smoke problems.

If competing interior mechanical devices and inadequate makeup air are behind your smoke issues, there are a variety of mechanical devices on the market that can help provide the necessary replacement air and balance the air pressure needs of your house system.

Have a Smoky Fireplace? Get to the Bottom of the Issue Fast With the Help of a Qualified Pro

Pinpointing the cause of a smoky fireplace isn’t always easy and straightforward. But it can be easy for you – just call on a CSIA-Certified Chimney Sweep®. When you see the CSIA logo, you can be confident that the individual coming out to inspect your chimney system is experienced, educated, trained, and ready to get to the bottom of the issue.

Find a CSIA-Certified Chimney Sweep® in your local area right here. And as always, if you have questions, we’re here to help. Simply reach out to us at office@csia.org or call 317-837-5362.


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