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Carbon Monoxide and Your Furnace: What to Do When the Alarm Sounds
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If the alarm is sounding right now
- Get outside. The NFPA says: if you hear the alarm, get outside immediately, then call the fire department. Do not go back inside unless the firefighters say it is safe.
- Check on everyone. Madison Fire asks whether anyone feels dizzy, sick or has flu-like symptoms. If yes, evacuate and call 911. The best first treatment for CO exposure is fresh air, then a doctor.
- Call 911 or the fire department from outside (NFPA, Madison Fire).
- Later, have a qualified heating contractor or your gas utility check the system (Madison Fire).
Madison Fire also lists a path for when nobody has symptoms: turn off gas appliances, open doors and windows, then call the gas utility or a qualified contractor. Our view: if you are unsure, leave and call 911. Leaving costs nothing.
Why a furnace can make CO
The NFPA says malfunctioning or improperly vented fireplaces, furnaces and generators can produce carbon monoxide, and that you cannot see or smell it. The CPSC lists home heating equipment among the sources and says poisoning is possible from poor maintenance, blocked venting or misuse.
Symptoms
The CDC lists headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion, often flu-like, and says people who are asleep may die before showing symptoms. The CPSC lists headache, dizziness, weakness, nausea, vomiting, sleepiness and confusion.
Alarms
| Question | What the sources say |
|---|---|
| Where? | On every level of the home and outside sleeping areas (CPSC, NFPA, CDC says near every sleeping area). |
| Which kind? | Battery-operated, or plug-in with battery backup. Interconnected alarms are best, so when one sounds they all sound (CPSC). |
| How often to test? | Push the test button each month (NFPA). CPSC: test monthly. |
| Batteries and age | CPSC: replace batteries every year, or choose sealed 10-year batteries. CDC: check batteries when you change the clocks and replace detectors per the maker's instructions or every 5 years. The two differ, so follow the label on your alarm. |
Sources: NFPA, CPSC, CDC. UL 2034 and listing marks are on your alarm's package; we did not open a source that explains them, so read the label.
Prevention
- The CDC says to have heating systems and other gas, oil or coal appliances serviced by a qualified technician every year. The CPSC and ENERGY STAR say the same about professional inspection.
- Never run a generator inside a home or garage, even with doors open. Run it outdoors at least 20 feet away (CPSC; Ready.gov gives the same distance).
- Never heat the house with a gas stovetop or oven (Ready.gov).
No carbon monoxide alarm yet?
CPSC and the NFPA say to have alarms on every level and outside sleeping areas. Look for a UL listing and read the label.
CO and your furnaceSee carbon monoxide alarmsAlarm went off and you're outside?
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When to call an HVAC technicianFind a licensed HVAC pro near youCommon questions
Can a furnace cause carbon monoxide poisoning?
Yes. The NFPA says malfunctioning or improperly vented furnaces can produce carbon monoxide. The CPSC says poisoning can come from poor maintenance, blocked venting or misuse.
What should I do first when my CO alarm goes off?
Get outside right away and call the fire department or 911. The NFPA says not to go back inside unless firefighters say it is safe.
Where should CO alarms go?
The CPSC says on every level of the home and outside sleeping areas.