How to Detect Carbon Monoxide without a Detector

• Black and yellow stains, yellow flames (instead of blue), and blown-out pilot lights in gas appliances can all be signs of a carbon monoxide leak.
• Condensation build-up on windows near gas appliances can also indicate a leak. If you have a fireplace, you might notice smoke build-up, too.
• Watch out for flu-like symptoms that occur specifically around gas appliances. This can be a sign of carbon monoxide poisoning.^[1]

Signs of a Carbon Monoxide Leak

Black or yellow stains around gas boilers, stoves, or fireplaces. Sooty stains or marks around your appliances mean there’s a loose connection and carbon monoxide could be leaking into your home. You may also notice black soot marks on front covers or panels on a gas fireplace.

Smoke buildup when you use your fireplace. If something is blocking your chimney when you burn a fire, the smoke won’t be able to vent out of your home properly. Since smoke can increase the levels of CO in your home, it can become hazardous if you leave the fire to burn. Even when you aren’t burning a fire, a clean chimney will have an upward draft you can feel when you open the flue. If you can’t feel a draft, it’s another warning sign that CO levels could build up.

Yellow flames on gas appliances. When you use a gas appliance, you’ll normally see blue flames which means all the gas is burning properly. If you see yellow or orange flames, or if burners aren’t fully igniting, it means there’s an issue with the gas and carbon monoxide could build up.

Pilot lights blowing out frequently. Pilot lights are small flames on furnaces, gas stoves, and water heaters that are always burning to help prevent gas leaks in your home. If you notice that your pilot light doesn’t stay lit or it flickers, it could mean CO has built up in the air around it. If the pilot light flame is blue, it could also be a sign that it’s not burning gas properly and CO is accumulating in the air.

Condensation buildup on windows near gas appliances. If you notice water droplets on the insides of the windows in a room with a gas appliance, it could mean that it’s not venting outside properly and CO is building up in your home.

What are the symptoms of carbon monoxide poisoning?

Mild CO poisoning has symptoms similar to the flu or food poisoning. When carbon monoxide levels are 50 parts per million (ppm), you’ll start to experience flu-like symptoms. You can tell if you have CO poisoning instead of the flu if you don’t have a fever when you have symptoms. If you feel any of the following symptoms, get to fresh air immediately and contact your doctor so they can treat your CO poisoning. Tension headache Dizziness or vertigo Fatigue or tiredness Confusion Difficulty breathing or shortness of breath Chest pains Stomach pains, nausea, or vomiting Loss of consciousness

Multiple people in your household will experience the same symptoms. You’ll notice everyone else you live with, including pets, getting sick around the same time if there’s carbon monoxide accumulating inside. If the symptoms were caused by the flu, one person would get sick before spreading it to someone else. People who spend more time indoors will be the most affected by the symptoms of CO poisoning.

Your symptoms will go away when you’re not near a CO leak. Since the carbon monoxide only builds up in enclosed spaces, you might notice your symptoms disappear when you’re not at home. Once you come back, the same symptoms will return.

Preventing Carbon Monoxide Buildup

Install carbon monoxide detectors throughout your home. Choose carbon monoxide detectors that are battery-powered or have a battery backup in case of a power outage, and get at least 1 for each story of your home. Since CO is slightly lighter than air, install the detectors 5 ft (1.5 m) above the floor and within 10 feet (3.0 m) of any bedroom so you can hear the alarm. Put the CO detector at least 15 feet (4.6 m) away from your kitchen or any other cooking appliances. Check or replace the batteries twice a year. After 5–7 years, replace the entire detector unit. When an alarm goes off, quickly leave and get to fresh air and check if you’re experiencing symptoms. Contact emergency services or your utility company to find the source of the leak or what caused the alarm to go off. It usually takes 60–90 minutes for CO detectors to go off when carbon monoxide levels are above 50 ppm. If there are extreme or deadly levels above 330 ppm, then the detector will go off within 2–3 minutes of exposure.

Have gas- or oil-burning appliances inspected annually. Hire a qualified appliance technician to look at all of your appliances that could potentially leak carbon monoxide, such as your oven, furnace, ventilation system, or water heater. They’ll be able to address any leaks or problems so that you stay safe when you use your appliances.

Clean your fireplace and chimney each year. Since soot can build up inside and prevent proper ventilation, take the time to clean your chimney. If you don’t feel comfortable cleaning your chimney by yourself, hire a professional service to come to clean it out for you to ensure the job gets done correctly. Whenever you use your fireplace, make sure you open the flue and wait to close it until the ashes feel cool so smoke can escape.

Open your garage door before you start your vehicle. Your vehicle’s exhaust also creates carbon monoxide and it can build up to dangerous levels in your garage. Keep your garage door open to let air flow through and back your car out into the driveway if you leave it idling so there’s no chance of CO accumulating inside.

Use gas appliances for their intended purposes only. Avoid using a gas stove, oven, or dryer to heat a room since it increases the risk of CO exposure and buildup.

Avoid using unvented gas appliances in enclosed spaces. Camping stoves and generators burn gas for power, but they don’t have exhaust vents to guide carbon monoxide outside. Only use these appliances outdoors or in a well-ventilated space with open windows so the carbon monoxide can properly dissipate without building up. Never use an unvented gas appliance anywhere where someone is sleeping. Avoid using unvented gas appliances for longer than 4 hours at a time.