Causes and Sign of Chimney Downdraft and How to Prevent It

smoke rising from the top of a chimney that does not have chimney downdraft issues
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smoke rising from the top of a chimney that does not have chimney downdraft issues

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Chimney downdraft is a serious problem that most homeowners encounter at one point or another. It can cause carbon monoxide detectors to go off, impair breathing, and impact your heating and cooling bills by hundreds of dollars per year.

If your chimney has a downdraft, you need to pay attention to it and develop a solution. Many new homeowners encounter these problems when they buy an older home where the fireplace wasn’t adequately maintained.

This outlines how your chimney works, why downdrafts are problematic, and what it could mean for your health if you don’t properly care for them.

What Makes a Chimney Work?

Your fireplace has a lot of working components above it in the chimney. There’s a smoke shelf, crown, cap, and most importantly, the chimney damper. Your chimney needs a damper to operate properly. It’s operable via a pull chain in your firebox or a small lever above it.

Your damper helps control the flow of smoke and allows it to rise through the flue, up through the cap, and out into the air. Chimneys operate on pressure caused by heat, so when there isn’t enough pressure, they don’t work well.

Downdraft is the number one problem created by improper pressure systems in your chimney. We’ll cover pressure and how to control it in this article.

What is Chimney Downdraft?

Chimney downdraft refers to when smoke no longer travels up the flue the way it’s supposed to. This causes smoke to come back down, or backdraft, into your living room and fill the house with dark smoke.

Sometimes backdraft gets confused with having a drafty fireplace, which is when cold air travels down from the top of your chimney and enters your home.

So what causes smoke to backdraft?

More often than not, it’s the damper. If yours is cracked or broken, you end up with backdraft issues caused by negative pressure building in the top half of your chimney. A strong second to this is the use of a fan that exhausts household air to the outside.

Signs of Chimney Downdraft

The wind comes down through your chimney, right past the damper, and brings those gusts of cold air, but how do you spot a problem before it gets worse?

These are a few signs to look out for:

Soot on Glass

Because of negative pressure systems in the home, a downdraft can send small particles of soot through the air. These typically roll into ordinary dust in the home, but the dark color is very visible on windows. If small soot stains are appearing on your windows, backdraft could be the culprit.

Carbon Monoxide/Smoke Alarms Appearing to Malfunction

If you don’t see an immediate and apparent threat, you might shrug off your smoke alarm. Instead, it could be a sign of low smoke levels entering your home caused by a downdraft.

Eye Irritation

Are your eyes bothering you when you’re near the fireplace, even when it’s off?

This may mean you’ve had a downdraft for a while, and the resulting soot is irritating your eyes.

How to Prevent Chimney Downdraft

Chimney downdraft is preventable with a few simple tips.

Shut Off Exhaust Fans: When your fireplace is in use, turn off your exhaust fans, as they naturally increase negative pressure by pulling air out of the house.

Adjust Your Damper: If your damper is warped, you might need to adjust it slightly to get the right airflow.

Try Opening A Window: This helps with negative pressure by providing potentially another path for air to enter the house instead of rushing down the chimney. Ironically, if two or more windows are open, try closing them. A breeze coming through these and crossing the room could also draw a vacuum in the house.

Check Chimney Height: Your chimney might be too short (especially if it’s an old home). Short chimneys cannot vent properly.

Clean Your Chimney: Soot and burned debris buildup can narrow passageways for the smoke to escape through your flue.

If you don’t have the equipment, time, or the ability to clean your chimney, it’s time to call in the professionals. Priddy Chimney Solutions can inspect your chimney for brick damage, damper wear, and ensure everything is operating the way it should. Annual chimney sweeps are the best method for maintenance.

What Causes a Downdraft?

Downdraft is caused by something called the stack effect, which is when warm air rises, leaving less air closer to the floor. In two-story homes or homes with attics, warm air creates a high-pressure point towards the top of your home.

Lower pressure points will attempt to regulate by pulling in air. Your fireplace is utilizing the air inside the room it’s located in, and in burning through that oxygen, it also creates a small vacuum. This isn’t necessarily bad, as long as there’s more oxygen (room or auxiliary air) to feed the flame.

When there’s not enough oxygen to burn, the low pressure tries to bring air in through the only available path: the chimney. So instead of acting as an exhaust vent, the chimney acts as an air intake.

The force of the air comes down and pulls smoke with it, resulting in a downdraft of smoke coming out into your living room.

Some examples of issues that cause downdrafts are:

Indoor Exhaust Fans: If the range fan in the kitchen or the fan in the bathroom is going, it’s pulling air out and creating that low-pressure system. Related to this are appliances that actively exhaust air to the exterior of the home, e.g. gas- or oil-fired furnaces or water heaters, attic fans, or dryers.

Recessed Lighting: It’s an excellent aesthetic addition to your home, but it’s not airtight. Warm air escapes and creates that negative pressure system.

Fix Your Chimney Downdraft

Chimney downdraft is a serious problem that can render your chimney completely useless. If you’re experiencing this problem or believe your chimney damper is malfunctioning, it’s in your best interest to inspect and potentially repair your chimney damper. When the DIY option doesn’t pan out, you have another option at your disposal.

Professional maintenance for your chimney is the best way to prevent downdrafts and other issues from occurring. Contact Priddy Chimney Solutions today to schedule regular chimney sweeps to clean and maintain everything from the flue to the firebox and beyond.

How can we help?

Our team is available to answer any of your chimney, fireplace, or masonry-related questions.

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