Carbon monoxide is colorless, odorless, and genuinely dangerous, which is exactly why a working detector matters more than any of your other senses when it comes to furnace safety. Here's what causes it, the symptoms to watch for, and exactly what to do if it happens.
If your carbon monoxide detector is alarming right now: leave the house immediately, get everyone into fresh air, and call emergency services from outside. Don't stop to investigate the source yourself.
A working carbon monoxide detector is the only reliable way to catch this hazard early.
What Causes Carbon Monoxide From a Furnace
Carbon monoxide is a byproduct of incomplete combustion. In a properly working furnace, it's produced in small amounts and safely vented outside through the flue. Problems arise when that venting system fails, or when the heat exchanger develops a crack that lets exhaust gases mix with the air circulating through your home.
Common Causes to Be Aware Of
A blocked or damaged flue, a cracked heat exchanger, improper combustion from a dirty burner, or inadequate ventilation around the furnace itself can all contribute to elevated carbon monoxide levels. None of these are things a homeowner can reliably diagnose without testing equipment.
Symptoms of Carbon Monoxide Exposure
Early symptoms can feel a lot like the flu: headache, dizziness, nausea, and fatigue. Because these symptoms are easy to dismiss, a detector is genuinely the only reliable warning system — by the time symptoms are obvious to everyone in the house, exposure levels may already be significant.
Why Detectors Matter More Than Your Nose
Unlike natural gas, which has an odor additive specifically so leaks are noticeable, carbon monoxide has none. This is why fire safety guidelines recommend a carbon monoxide detector on every level of your home, particularly near sleeping areas, rather than relying on smell or symptoms to catch a leak.
What to Do If Your Detector Alarms
Treat every alarm as real until proven otherwise. Get everyone, including pets, outside into fresh air right away, and call emergency services from outside the home rather than staying to investigate. Don't go back inside until authorities or a qualified technician confirm it's safe.
After the Alarm: Don't Skip the Inspection
Even if the alarm turns out to be a false one, or levels return to normal, have the furnace professionally inspected before running it again. A full combustion safety inspection confirms whether it's actually safe to restart, rather than just hoping the reading was a fluke.
Carbon Monoxide Safety at a Glance
Here's a quick summary to keep handy.
| Situation | What to Do |
|---|---|
| Detector alarms | Leave immediately, call emergency services from outside |
| Flu-like symptoms with no other cause | Leave the house and seek fresh air |
| No detector installed | Install one on every level, especially near bedrooms |
| After any alarm event | Have the furnace professionally inspected before restarting |
Furnova Furnace Repair, the area's expert service provider, includes a combustion safety check on every service visit, since this is one hazard that's never worth leaving to chance.
Carbon monoxide safety isn't something to handle reactively. A working detector, paired with regular furnace maintenance, is by far the most effective way to prevent this from ever becoming an emergency in the first place.