Can Your Fireplace Cause Carbon Monoxide Poisoning? | Widen Chicago

Carbon monoxide is a colorless, odorless, deadly gas produced whenever fuel—wood, gas, or other combustibles—burns incompletely. In a properly functioning fireplace, combustion gases exit through the chimney to the outdoors. But when ventilation is compromised, CO accumulates indoors.

Here's what happens in a normal, safe fireplace:

• Fuel burns in the firebox
• Hot combustion gases rise naturally (or are pushed by fans in gas fireplaces)
• Gases exit safely through the chimney and vent to the outside air
• Fresh air is drawn in to replace the exiting gases, maintaining safe oxygen levels inside

When this ventilation chain breaks—due to a blocked chimney, cracked flue, missing chimney cap, or closed damper—CO begins to accumulate inside your home. Even small concentrations can be dangerous over time, particularly for children, elderly individuals, and people with respiratory or cardiac conditions.

Wood-Burning Fireplaces

Traditional wood-burning fireplaces are the highest risk for CO issues. Several factors make them vulnerable:

• Incomplete combustion: Wood doesn't always burn completely, especially with damp wood or poor airflow
• Creosote buildup: Wood combustion produces creosote, a sticky, flammable residue that accumulates inside the chimney and restricts airflow
• Blockages: Aging mortar, animal nests, debris, and structural deterioration commonly block wood-burning chimney flues
• Older construction: Many Chicago homes have wood-burning fireplaces installed decades ago in chimneys that have never been modernized

Chicago's harsh winters mean high fireplace usage, compounding the risk. Older homes with century-old chimneys are particularly vulnerable.

Gas Fireplaces

Modern gas fireplaces are safer than wood-burning units because they burn more completely and produce less CO. However, they're not risk-free:

• Faulty seals or cracks in the firebox or venting pipes leak CO
• Blocked vents or exhaust pipes prevent gases from exiting
• Improper installation or maintenance increases danger
• Older gas fireplace units may not meet current safety standards

Electric Fireplaces

Electric fireplaces cannot produce carbon monoxide. They use electric resistance heating or forced hot air without any combustion process. If CO poisoning is your primary safety concern, electric fireplaces eliminate that specific risk entirely.

CO poisoning symptoms mimic flu and other common illnesses, which is why it's called the "silent killer." Early recognition is critical:

Mild to Moderate Exposure

• Headache (frontal area pressure)
• Dizziness or lightheadedness
• Nausea and vomiting
• Fatigue and weakness
• Shortness of breath
• Confusion or difficulty concentrating

Severe Exposure

• Loss of consciousness
• Seizures
• Cardiac arrest
• Death

If you suspect CO poisoning: Leave the home immediately and go to fresh air. Call 911 from outside. Do not re-enter until emergency personnel confirm the home is safe. Even if symptoms seem mild, seek medical evaluation—CO can cause permanent brain and heart damage.

Blocked or Restricted Chimneys

A blocked flue is the most common cause of dangerous CO accumulation. Blockages occur from:

• Creosote buildup in wood-burning chimneys (layers of flammable residue)
• Bird nests, leaves, or animal debris entering through open tops
• Crumbling mortar joints or brick deterioration (especially in 50+ year old chimneys)
• Missing or damaged chimney caps

Cracked or Damaged Flues

The flue (the interior passage of the chimney) is where combustion gases travel. Cracks allow CO to seep into walls and adjacent rooms before reaching the outside. Chicago's freeze-thaw cycles accelerate flue deterioration.

Closed Dampers During Fireplace Use

Never, under any circumstances, close the damper while your fireplace is in use or has hot coals. The damper is a metal plate that closes the chimney opening. When closed during fires, it traps CO and other combustion gases inside your home. Wait until all coals are completely cool and ash is cold before closing the damper.

Negative Pressure in the Home

Modern homes are built tightly sealed for energy efficiency. HVAC systems, exhaust fans, and dryers create negative pressure that can reverse the natural draft in chimneys, forcing gases back into living spaces.

1. Schedule Annual Chimney Inspections

The NFPA mandates annual inspection and cleaning for all chimneys, fireplaces, and venting systems. A professional chimney inspector:

• Visually examines the interior and exterior flue
• Detects cracks, deterioration, and blockages
• Measures creosote buildup
• Identifies draft problems
• Documents findings to protect your family and home

Schedule a professional chimney inspection with Widen Chicago before the heating season begins. Don't skip this—it's the single most important prevention step.

2. Keep Chimneys Clean

Professional chimney cleaning removes creosote buildup, nesting materials, and debris. How often do you need cleaning? Read our guide on chimney cleaning frequency. Most Chicago homes using wood-burning fireplaces need cleaning 1-2 times annually.

3. Install and Maintain Chimney Caps

A missing chimney cap is an open invitation for animals, rain, and debris to enter the flue. Caps prevent:

• Bird and squirrel nests (major blockage cause)
• Rainwater entry (causes deterioration)
• Debris accumulation
• Downdrafts during high winds

Caps should be inspected annually and replaced if damaged.

4. Ensure Proper Ventilation

Your home needs a supply of fresh air to replace gases exiting through the chimney. In tightly sealed homes:

• Slightly crack a window near the fireplace when in use
• Don't block HVAC returns or vents
• Have a professional evaluate your home's air balance

5. Install Carbon Monoxide Detectors

CO detectors are your last line of defense. Install them:

• On every level of your home
• In hallways near sleeping areas
• Within 10 feet of fireplaces or other appliances that produce heat/combustion
• In multi-story homes, include both ground and upper floors

Check detectors monthly, replace batteries twice yearly, and replace the unit itself every 5-7 years. Many CO detectors have expiration dates printed on them.

6. Never Use Your Fireplace as a Heating Source

Fireplaces are inefficient and can actually lose heat. Prolonged operation (especially with inadequate ventilation in heating mode) increases CO risk. Use fireplaces for occasional warmth and ambiance, not primary heating.

7. Avoid Common Dangerous Practices

• Don't close the damper with hot coals or fire
• Don't burn treated wood, plastic, or wet wood
• Don't use your fireplace if you suspect a blockage or damage
• Don't ignore CO detector alarms

1. Evacuate immediately. Get everyone outside to fresh air.
2. Call 911 from outside the home.
3. Don't re-enter the home until emergency responders confirm it's safe.
4. Get medical attention even if symptoms are mild.
5. Contact a professional chimney service to inspect and repair the problem before using the fireplace again.