Carbon Monoxide: The Invisible Furnace Danger
Every winter in Minnesota, furnaces run around the clock—and every winter, carbon monoxide (CO) poisoning sends hundreds of people to emergency rooms. CO is produced when fuel combustion is incomplete. A properly functioning furnace vents all CO outside. A cracked heat exchanger, blocked flue, or failing burner can let CO leak into your living space.
You can't smell it. You can't see it. At low levels it causes headaches and nausea that people mistake for the flu. At high levels it kills within minutes.
How Your Furnace Produces Carbon Monoxide
Natural gas furnaces burn methane to produce heat. Complete combustion yields CO2 and water vapor—both safely vented outside. Incomplete combustion yields carbon monoxide (CO), which is toxic. Incomplete combustion happens when the air-fuel mixture is off, the heat exchanger is cracked, the flue pipe is blocked or disconnected, or burners are dirty or corroded.
The Cracked Heat Exchanger: Biggest CO Risk
The heat exchanger separates combustion gases from your breathing air. A crack lets those combustion gases—including CO—contaminate the air blowing into your home. Heat exchangers crack due to age, overheating from restricted airflow, metal fatigue, and corrosion. Learn more in our guide to cracked heat exchangers: risks, signs, and what to do in Minnesota.
Symptoms of Carbon Monoxide Poisoning
CO poisoning symptoms vary by concentration and exposure time. Low-level chronic exposure causes persistent headaches, fatigue, and slight nausea—often dismissed as a cold or flu. Moderate exposure causes severe headache, drowsiness, and disorientation. High-level acute exposure causes loss of consciousness and can be fatal. A key clue: symptoms improve when you leave the house. If multiple family members feel sick simultaneously in winter, get everyone out immediately and call 911.
CO Detector Requirements in Minnesota
Minnesota law requires CO detectors in all dwellings with fuel-burning appliances. Detectors must be installed within 10 feet of every sleeping area. Even if not legally required, CO detectors are non-negotiable in any Minnesota home with a gas furnace running 6+ months per year.
Where to Place CO Detectors
Place detectors near each sleeping area, on each level of the home, and near the furnace room. Most experts recommend one detector per floor plus one near the mechanical room—typically 3-4 detectors in a two-story Minnesota home.
CO Detector Types and Lifespan
Electrochemical sensors are the most accurate and reliable technology. Look for UL-listed detectors from Kidde or First Alert in the $25-$60 range. CO detectors last 5-7 years—replace them on schedule regardless of whether they've alarmed. A detector that's 8 years old may not respond to a dangerous CO leak.
What to Do When Your CO Alarm Sounds
Get everyone out immediately. Leave the door open to help ventilate the home. Call 911 from outside. Don't re-enter until cleared by emergency responders. Get medical attention if anyone has symptoms. Have the furnace inspected before running it again. Treat every alarm as real until proven otherwise.
Annual Furnace Inspection: Your Best Prevention
CO detectors are your safety net—annual furnace inspection is your prevention. A qualified technician will inspect the heat exchanger for cracks, check flue pipes for blockages, clean burners, test combustion efficiency, and check draft and venting. See our guide to furnace tune-up cost in Minnesota.
Furnace Age and CO Risk
Older furnaces carry higher CO risk. Heat exchangers degrade over time—15-20+ year furnaces have much higher crack risk. If your furnace is 15+ years old, CO risk is a real factor in the replacement decision. A new high-efficiency furnace with sealed combustion dramatically reduces CO risk while cutting heating bills. See our guide to furnace lifespan in Minnesota.
Sealed Combustion Furnaces: Lower CO Risk
Modern high-efficiency furnaces (90%+ AFUE) use sealed combustion—they draw combustion air directly from outside through a PVC pipe. This means combustion air supply can't be depleted in a tight house and depressurization can't backdraft flue gases. Sealed combustion systems are inherently safer than traditional atmospheric furnaces. See our Goodman GMVC96 review.
The Bottom Line on CO Safety
The combination of annual professional maintenance, working CO detectors on every floor, and a modern furnace with sealed combustion gives you layered protection against carbon monoxide. Furnace Direct offers Goodman furnaces direct from the factory with same-day Minneapolis/St. Paul delivery. Browse our Goodman furnace selection.
Related: Minnesota furnace emergency guide | Furnace safety devices explained
Do you know your model number?
Search your exact replacement — or let us match you to the right unit in 60 seconds.
Search by Model
Enter your furnace or AC model number to find your exact factory-direct replacement.
Take the 60-Second Quiz
Answer 4 quick questions and we'll match you to the right furnace for your home and budget.
🏠 Take the 60-Second QuizGet installed pricing on a new system.
Tell us a little about your home and what you're replacing. We'll send real numbers on a Goodman 96% AFUE setup — equipment shipped nationwide, licensed install in select metros. No contractor markup, no obligation.