Carbon Monoxide and Furnace Safety

If your CO alarm sounds

Never assume a sounding alarm is a false alarm. Treat every activation as real until responders confirm otherwise.

1. Get everyone, including pets, outside to fresh air immediately.
2. Call 911 or your gas utility from outside the home.
3. Do not re-enter until emergency responders say it is safe.
4. Seek medical attention if anyone has headache, dizziness, nausea, confusion or weakness.
5. Have the combustion appliances professionally inspected before the system is used again.

Recognizing the symptoms

Carbon monoxide exposure produces symptoms that mimic the flu: headache, dizziness, nausea, fatigue, shortness of breath and confusion — but without a fever. A pattern worth paying attention to is symptoms that improve when you leave the house and return when you come back, or multiple household members feeling unwell at the same time.

Infants, older adults, pregnant people and anyone with heart or respiratory conditions are more vulnerable.

Furnace-related causes

• A cracked or corroded heat exchanger allowing exhaust into the air stream
• A blocked, disconnected or deteriorated vent pipe
• Inadequate combustion air supply in a tightly sealed space
• Improper venting or installation errors
• A bypassed pressure switch allowing operation with a blocked vent
• Backdrafting caused by strong exhaust fans depressurizing the home
• Incomplete combustion from dirty burners or incorrect gas pressure

Alarm placement and maintenance

Combination smoke and CO alarms are convenient, but confirm the CO sensor's expiration date separately. Many homeowners are surprised to learn an alarm that still chirps and lights up may have an expired sensor.

• Install alarms on every level of the home, including the basement
• Place an alarm near each sleeping area so it will wake occupants
• Follow the manufacturer's instructions for mounting height and clearances
• Keep alarms away from immediate proximity to combustion appliances to avoid nuisance activations
• Test monthly and replace batteries as recommended
• Replace the alarm itself at the end of its rated service life — sensors expire

Prevention through maintenance

Annual professional service that includes heat exchanger inspection, venting verification and combustion assessment is the practical prevention strategy. Add the homeowner habits that keep airflow healthy — filter changes, clear returns and open registers — because chronic overheating is a leading contributor to heat exchanger failure. See furnace maintenance and the winter furnace checklist.

Other CO sources in the home

Furnaces get the attention, but water heaters, gas ranges, fireplaces, wood stoves, generators and vehicles idling in attached garages all produce carbon monoxide. Never run a generator or a vehicle in an attached garage, even with the door open, and never use a stove, oven or outdoor grill as a heat source indoors. This applies especially during a no-heat emergency.