Carbon Monoxide Alarm Going Off

A carbon monoxide alarm activation is a life-safety emergency. Do not assume it's a false alarm. Carbon monoxide is colorless, odorless, and can cause unconsciousness or death in minutes at high levels. HVAC equipment — gas furnaces, water heaters, generators, gas ranges — is the most common indoor source. Here's exactly what to do right now, then what likely caused it.

Most Likely Causes

1. Cracked heat exchanger in a gas furnace

The most common HVAC-related CO source. When the heat exchanger cracks, combustion gases (including CO) that should vent up the chimney instead leak into the supply air stream and get blown throughout the house. Age of furnace, thermal fatigue, and rust are the usual causes. Requires flue gas analyzer testing to confirm.

2. Blocked or backdrafting flue

If the flue is blocked by a bird nest, collapsed section, ice buildup, or is backdrafting due to a pressure imbalance in the home, combustion products including CO can spill into the space instead of venting outside.

3. Improper combustion air supply

Furnaces need adequate combustion air. If the furnace is in a small closet without proper air openings, or if a bathroom exhaust fan or range hood is creating negative pressure, combustion can go incomplete and produce CO.

4. Water heater or gas appliance issue

The CO source might not be the furnace — gas water heaters, gas ranges, gas fireplaces, and generators (especially if a generator is running in an attached garage) are all potential sources. Any gas-burning appliance that's malfunctioning can produce CO.

5. Dying CO detector (last check, not first)

CO detectors have a 5-7 year lifespan. After that, sensor drift can cause false alarms. However, never assume a false alarm without evacuating first and testing with professional equipment. The cost of being wrong is fatal.

Try These Steps Before You Call

• 1. Get everyone outside immediately — people and pets. Do not stop to gather belongings.
• 2. Call 911 if anyone is showing symptoms: headache, dizziness, nausea, confusion, weakness, chest pain, or loss of consciousness. Firefighters have professional CO meters and can test the air.
• 3. If no symptoms, call your gas utility from outside (Atmos Energy: 866-322-8667). They will dispatch a response team with detection equipment.
• 4. Do not re-enter the home until emergency responders declare it safe.
• 5. Once safe, call us to inspect the HVAC system with a calibrated flue gas analyzer. We test for CO at supply registers, inspect the heat exchanger for cracks, verify flue integrity, and check combustion air adequacy.
• 6. Replace any CO detector older than 5-7 years (check the manufacture date on the back).
• 7. Do not restart the furnace until it has been professionally inspected and cleared. Use portable electric heat in the interim if needed.

Other Common Heating Problems

See also: AC problems