Furnace Carbon Monoxide Risk: What Every Minnesota Homeowner Must Know

Carbon monoxide (CO) from a malfunctioning furnace kills approximately 400 Americans every year and hospitalizes thousands more. In Minnesota, where furnaces run for six or more months annually and homes are tightly sealed against cold, the risk is heightened. This guide covers everything you need to know to protect your family.

Why Furnaces Produce Carbon Monoxide

Combustion of natural gas or propane produces CO as a byproduct whenever combustion is incomplete. In a properly operating furnace:

• The heat exchanger completely separates combustion gases from living space air
• Combustion is efficient — very little CO is produced
• All combustion byproducts are safely vented to the outdoors

Problems occur when any of these conditions fail. Common causes of CO leakage from furnaces:

• Cracked heat exchanger — allows combustion gases to mix with supply air (most common serious cause)
• Blocked or restricted flue — prevents exhaust from escaping, causing backdrafting into living space
• Incomplete combustion — yellow/orange flames instead of blue indicate incomplete combustion and elevated CO production
• Improper venting installation — negative pressure in tight homes can pull exhaust back through atmospheric vents
• Oversized furnace short-cycling — rapid on/off cycles prevent complete combustion

CO Symptoms: Know the Warning Signs

Carbon monoxide is odorless and colorless — you cannot detect it without a detector. Symptoms of CO poisoning are often mistaken for flu:

Key warning sign: Symptoms improve when you leave home and return when you're inside. This pattern strongly suggests CO from a home appliance, not illness.

CO Detectors: Minnesota Law and Best Practice

Minnesota law (Statute 299F.50) requires CO alarms in all single-family dwellings and multi-family units with fossil fuel appliances. Required placement:

• On each level of the home that contains a sleeping area
• Within 10 feet of each sleeping room
• In any room with a gas appliance adjacent to a sleeping area

CO detectors have a service life of 5–7 years. Check the manufacture date on the back of any existing detectors — if they're over 7 years old, replace them immediately. The sensors degrade over time even if they don't visually appear damaged.

Best practice beyond code minimums:

• Install a CO detector in the mechanical room near the furnace
• Use combination smoke/CO detectors throughout the home
• Choose detectors with digital CO level readouts rather than simple alarm-only models (so you can see low-level accumulation)

What to Do If Your CO Detector Alarms

1. Evacuate immediately — everyone out, including pets. Don't stop to investigate.
2. Leave the door open as you exit — helps ventilate
3. Do not re-enter for any reason
4. Call 911 from outside or a neighbor's phone
5. Call your gas utility's emergency line
6. Do not return until the fire department has cleared the home and a technician has identified and fixed the source

Annual Furnace Inspection: Your Best Protection

The single most effective way to prevent CO from your furnace is an annual professional inspection that includes:

• Heat exchanger inspection for cracks
• Combustion analysis (CO measurement in flue gases)
• Flue and venting inspection for blockage or damage
• Burner inspection for proper flame color and pattern

If your technician uses a CO analyzer and measures combustion gases as part of the tune-up, you have meaningful data. If they just look and leave, it's a visual inspection — less reassuring. Ask specifically whether combustion analysis is included. See what a proper tune-up includes.

High-Efficiency Furnaces: Lower CO Risk

Modern direct-vent sealed combustion furnaces (all Goodman 96%+ models) have a significant safety advantage: combustion air comes through a dedicated outdoor pipe, and exhaust exits through another. There is no reliance on indoor air for combustion and no shared pathway between combustion gases and indoor air except through the heat exchanger itself. Backdrafting risk is essentially eliminated.

If you have an older 80% AFUE atmospheric furnace in a tightly-sealed home, the risk of backdrafting is real — especially in newer construction. Upgrading to a sealed combustion unit eliminates this pathway entirely.

Replacing an Older Furnace for Safety

If your furnace is over 15 years old, consider proactive replacement rather than waiting for a failure — the risk of heat exchanger cracking increases significantly with age. Furnace Direct offers factory-direct pricing on Goodman sealed combustion furnaces with same-day Minnesota delivery.

Related: Cracked Heat Exchanger Guide | Combustion Air Requirements | Furnace Smell Guide