Carbon monoxide (CO) is a gas you cannot see, smell or taste. It comes from burning fuel, including natural gas and propane. A gas furnace that is working right sends its exhaust safely outside. A furnace with a problem can let CO into your home. According to the U.S. Consumer Product Safety Commission (CPSC), more than 200 people in the U.S. die every year from accidental non-fire CO poisoning linked to consumer products.
This is the time of year to take it seriously, before the furnace runs every day.
Which homes are at risk?
Any home with a fuel-burning appliance: a gas or propane furnace, gas water heater, gas range, gas fireplace or an attached garage. Heat pumps and electric furnaces do not burn fuel, so they do not make CO. Many all-electric homes still have a gas water heater or fireplace, so CO alarms make sense there too.
How a furnace can leak CO
- A cracked heat exchanger. The heat exchanger keeps combustion gases separate from the air you breathe. Cracks develop with age and overheating.
- A blocked or disconnected vent pipe. Bird nests, debris, or a pipe that has come apart can send exhaust back into the house.
- Poor combustion. Dirty burners or the wrong gas pressure can produce more CO.
Warning signs at the furnace
- A yellow or flickering flame instead of a steady blue one
- Soot or scorch marks around the furnace or vent
- Rust or water streaks on the vent pipe
- A furnace that shuts itself off often
- A CO alarm that sounds, even once
Symptoms of CO exposure
The CPSC lists headache, dizziness, weakness, nausea, vomiting, sleepiness and confusion. It can feel like the flu without a fever. A clue is when several people in the house, or pets, feel sick at the same time and feel better after leaving home.
If your CO alarm sounds
- Get everyone outside to fresh air right away.
- Call 911 from outside.
- Do not go back in until responders say it is safe.
- Do not use the furnace again until it has been inspected and repaired.
Where to put CO alarms
The CPSC recommends battery-operated CO alarms, or alarms with battery backup, on every level of the home and outside sleeping areas. Test them monthly. Alarms have an end-of-life date printed on them. Replace them by that date.
Smell gas? That is different
Natural gas has a rotten egg smell added so you can detect leaks. CO has no smell at all. If you smell gas, do not flip switches or use your phone inside. Leave the house and call your gas utility or 911 from outside.
Why a yearly furnace check matters
A furnace tune-up is the best time to catch CO risks early. A good inspection looks at the burners and flame, the heat exchanger, the vent pipe and draft, and safety switches. If your furnace is more than 15 years old, or you have never had it checked, now is a good time. Learn about our furnace maintenance and our fall HVAC checklist.
Call North Alabama Heating & A/C at (256) 534-2941. We have served Huntsville, Madison and North Alabama since 1977, Monday to Saturday, 7 AM to 7 PM.
Quick answers
Can a furnace leak carbon monoxide?
Yes. A gas or propane furnace can leak CO if the heat exchanger is cracked, the vent pipe is blocked or disconnected, or the burners are not burning cleanly. A yearly inspection and working CO alarms are the best protection.
What are the signs of carbon monoxide from a furnace?
Look for a yellow or flickering flame, soot around the furnace, rust or water on the vent pipe, and a furnace that shuts off often. People may have headaches, dizziness or nausea that improve away from home. A CO alarm is the only reliable way to know.
Do heat pumps produce carbon monoxide?
No. Heat pumps and electric furnaces do not burn fuel, so they do not produce carbon monoxide. Other gas appliances in the home still can, so CO alarms are still a good idea.
