Carbon monoxide, often referred to as "CO," is a colorless, odorless gas emitted from appliances that burn fossil fuels like wood, natural gas, oil, propane, kerosene, and coal. This gas can originate from any kind of fuel combustion. It's important to distinguish between carbon monoxide (CO) and carbon dioxide (CO2), which is what we exhale when we breathe. Interestingly, this process is reversed in plants, which absorb carbon dioxide and release oxygen.

Understanding the risks associated with carbon monoxide and how carbon monoxide detectors work can help protect you and your home. Unfortunately, there’s a large level of confusion related to this dangerous gas and the tools that detect it. This leads to people thinking they’re protected when they’re really not, and many others have unwarranted fears that can turn expensive.

It's important to note that detecting or testing for carbon monoxide falls beyond the scope of a standard home inspection; however, home inspectors are required to note whether carbon monoxide and smoke detectors are present during a home inspection.

Carbon Monoxide is a Serious Health Risk


Carbon monoxide poses a significant health risk because when inhaled, it binds with the hemoglobin in the blood that normally carries oxygen, forming carboxyhemoglobin (COHb). This process blocks the essential delivery of oxygen to the body's vital organs, including the brain. A key indicator of carbon monoxide poisoning could be if you notice that several or all members of your household, including pets, are experiencing symptoms like the flu, including dizziness, nausea, headaches, tiredness, vomiting, and confusion. One of the risks associated with CO poisoning is the gradual onset of these symptoms, making them hard to detect promptly. Experiencing a loss of consciousness is a sign of severe, high-level exposure to carbon monoxide. Alarmingly, if carbon monoxide poisoning occurs while sleeping, there is a risk of not waking up. The after-effects of exposure to this gas can result in serious health issues, such as brain and heart damage, or even be fatal.

Homes equipped with fireplaces, furnaces, gas water heaters, gas stoves/ovens, boilers, and similar appliances could pose a risk of carbon monoxide poisoning to those living there. Additionally, even homes without these appliances but with an attached garage might be at risk due to car exhaust fumes infiltrating the living spaces. Carbon monoxide exposure is a serious health hazard for both humans and animals. The Center for Disease Control (CDC) reports that annually, over 400 Americans succumb to carbon monoxide poisoning not associated with fires, with more than 20,000 emergency room visits and over 4,000 hospitalizations. The Environmental Protection Agency (EPA) identifies carbon monoxide as the leading cause of fatal poisonings in the U.S. Understanding and recognizing the symptoms of CO poisoning is essential for everyone's safety.

For many homeowners, it has become second nature to simply disconnect their alarm when it goes off. You should never do this as it can result in dire consequences. Instead, try to pinpoint the source of carbon monoxide. If it's an appliance, turn it off and allow your home to air out. You can reset your CO detector to see if the issue persists, but you should never unplug or disconnect it. If you can’t find the source, call 911 to have your local fire department check it out.

CO Detectors Don’t Detect Natural Gas

While there are adverse health effects from carbon monoxide and natural gas, it’s important to recognize that these aren’t the same substances. CO is a byproduct – natural gas is not. Because of their differences, a carbon monoxide detector will not typically alarm for natural gas. Unfortunately for homeowners and families, both these gases can lead to suffocation and fires – although the risk of fire is much higher with natural gas, making it a good investment for detectors that monitor both carbon monoxide and natural gas.

Carbon Monoxide is Odorless

While having multipurpose detectors is ideal, it’s important to recognize why most detection devices check for carbon monoxide and not natural gas. Even though natural gas is far more combustible, companies add mercaptan to help identify leaks. Mercaptan is a harmless chemical, but whenever it hits your nose, you’ll recognize the smell of rotten eggs almost immediately. Carbon monoxide is odorless, so you won’t typically have any sensory warning about its presence.

Carbon Monoxide Comes from Multiple Sources

People often believe that they’re at no risk of carbon monoxide poisoning unless they have certain gas appliances. This is a common misconception that can lead to delayed response when a situation is becoming an emergency. Common sources of carbon monoxide include:

  • Kerosene heaters
  • Furnaces
  • Dryers
  • Lawn mowers
  • Stoves
  • Gas ranges
  • Fireplaces or other wood-burning devices
  • Grills or other charcoal-burning devices
  • Portable generators
  • Vehicles idling in garages

Around 60 percent of unintentional CO deaths are linked to motor vehicle exhaust – something everyone encounters regardless of their appliances. Due to the variety of carbon monoxide sources, you’ll encounter at home, it’s never a bad idea to have a professional home inspection performed to pinpoint potential dangers.

Appliances like fireplaces, furnaces, boilers, and non-electric water heaters should have their exhaust directed either to a chimney or directly outside. If these appliances use a chimney, it's critical to have it professionally cleaned and inspected every year. Many homeowners overlook this annual maintenance, not realizing that blockages from leaves, debris, or animal nests in chimneys can cause exhaust gases to back into the home, often leading to carbon monoxide poisoning.

There are vent-free gas and propane fireplaces available. These don't need an exhaust vent as they are designed to completely burn the fuel and are equipped with an oxygen depletion sensor to monitor air quality. However, there have been instances where these sensors fail. Hence, homeowners should be advised against using vent-free appliances indoors, and some states even prohibit them. These appliances often instruct users to open a window for adequate air, but this advice is commonly ignored.

For fireplaces, make sure the damper is open before use. If you have a gas or propane fireplace with a pilot light and a damper, a clip should be installed to prevent complete closure of the damper, as CO can accumulate from a pilot light in an unventilated space. Also, use cleaning solvents like paint thinner only outdoors, as they can sometimes produce CO.

Additionally, never use generators or grills inside your home, basement or garage. Always operate them outdoors in well-ventilated areas. Likewise, only run vehicles in a garage with the door open and avoid using gas or propone stoves or ovens as heating sources.

Ensuring appliances like your furnace and water heater have enough combustion air is vital. Home inspectors commonly find improperly enclosed appliances in basements, which can lead to oxygen depletion and increased fire risk, especially if combustible items are stored nearby. If you're finishing a basement, always start with a permit and ensure the utility room is adequately sized to operate your appliances safely, with proper vents for airflow.

Finally, attached garages should have a fire-separation wall (or 'firewall') between them and living spaces. This not only slows the spread of fire, but also helps prevent CO from seeping from the garage into living areas. Seal any gaps where wiring, ductwork, or plumbing goes through these walls or ceilings, and avoid heating registers in the garage to prevent fire or CO from entering the home through the ducts.

Not All Alarms Require 911

While you should always call 911 in an emergency, the Belvidere Fire Department in Illinois points out that this isn’t always necessary every time your CO detector goes off. If no one in the home is experiencing flu-like symptoms such as dizziness, nausea or headaches, the risk of serious exposure isn’t that high.

In these situations, they recommend turning off all gas-burning equipment and appliances. The area should be properly ventilated and the alarm reset. An inspector can examine these appliances and determine which is causing the problem. If anyone in your family is experiencing flu-like symptoms, you should evacuate immediately and call 911.

A Silent Alarm Doesn’t Mean You’re Safe

Once you ventilate your home, the high levels of gas that set off your carbon monoxide detector may no longer be present. This may remain the case even if you turn back on the appliances that potentially set it off in the first place. Just because the alarm doesn’t immediately go off, doesn’t mean the risk is gone.

The fact is that carbon monoxide can occasionally take time to build up to unsafe levels. Additionally, a problem with an appliance may be infrequent and only create the high concentration of CO in a home intermittently. This means you should never assume your detection device was malfunctioning simply because it doesn’t immediately go off again.

If you can’t pinpoint why your detector went off, this is another situation where you shouldn’t be afraid to call 911. Emergency services typically receive over 80,000 non-fire carbon monoxide calls yearly, so you should never view your concern as an inconvenience – they’re used to these calls!

Carbon Monoxide Can Cause Fires


While suffocation is the biggest concern linked to carbon monoxide exposure, it’s important to understand that CO can also cause fires. It is a combustible gas with a Lower Explosive Limit (LEL) of 12.5 percent - which is the lowest concentration of a gas in the air to cause fire. Propane's LEL is only 2.2 percent. Even considering the low risk of combustion, this is yet another reason why nearly every structure needs carbon monoxide detectors. It also explains why turning off all gas-burning appliances when CO is detected is imperative.

There are Areas that Don’t Need Detectors

It’s recommended – and required in some states – that a carbon monoxide detector be placed in every bedroom of a house. Two-story homes should have a detection device on each floor, and one should also be placed at the top of basement stairs.

There are also a few spots where CO detectors shouldn’t be placed, including:

  • Areas with extreme temperatures (e.g. unfinished attics, unconditioned crawl spaces)
  • Kitchens
  • Garages
  • Furnace rooms
  • Areas that are humid, greasy, dirty or dusty
  • In direct sunlight
  • In outlets with obstructions (e.g. curtains)
  • Near turbulent air that could blow CO away from detector (e.g. fans, heating vents)

Each of these areas could result in false alarms due to temporary normal buildups of CO (e.g., in a garage) or prevent your detection device from doing its job. Avoid these spots and read the instructions for your carbon monoxide detector carefully to ensure your safety.

Alarms Could Indicate an Unidentified Fire

Carbon monoxide is a significant danger in house fires. If part of your home is ablaze, it’s likely that you don’t need a CO detector to warn you of the hazard. In some situations, though, a carbon monoxide alarm could indicate a small ongoing fire that you may not know is happening. This is a serious danger with chimney fires. They often don't have enough fuel or air to be immediately detectable or dramatic. Basement and garage fires also have a high likelihood of not being detected before serious damage can occur. Unfortunately, unidentified fires can still cause serious structural damage and pose a risk of carbon monoxide exposure that’s difficult to pinpoint.

Winter Presents Even More Danger

Winter spans from December to March, and this is when the most significant dangers related to carbon monoxide exist. On average, half of reported CO incidents during the year occur between November and February. January is the worst month for carbon monoxide incidents, with December coming in at a close second.

The reasoning being is gas-powered furnaces see increased usage during winter months. Additionally, people are more likely to incorrectly use appliances as heating sources, including propane stoves, portable generators and grills, if a power outage occurs. This makes it imperative to ensure all gas-burning equipment is in proper working order and used appropriately.

How Carbon Monoxide Detectors Work

Carbon monoxide detectors operate by detecting the gas produced from the incomplete burning of carbon-containing materials - unlike smoke detectors which only identify smoke particles through the use of light beams. CO detectors are crucial for enclosed areas that can trap the gas and allow it to buildup.

CO detectors don't immediately sound an alarm upon detecting CO. Industry standards stipulate that they must alarm within 60 to 240 minutes at a concentration of 70 ppm, within 10 to 50 minutes at 150 ppm, and within 4 to 15 minutes at 400 ppm.

Carbon monoxide exposure is measured in parts per million (ppm). The Occupational Safety and Health Administration (OSHA) sets a maximum allowable exposure of 35 ppm over 8 hours. Exposure to 200 ppm for 2 hours can cause symptoms like fatigue, headaches, nausea, and dizziness, while 800 ppm for the same duration can lead to unconsciousness or even death. Exposure to over 1,000 ppm for 20 minutes or less can be fatal. It's crucial to act quickly if exposed to carbon monoxide.

Every home should be equipped with at least one carbon monoxide (CO) detector. It's important to avoid placing CO detectors near ceiling fans, the high points of cathedral ceilings, or close to exterior doors and windows, as these locations can hinder the detector's ability to sense dangerous exhaust gases. CO detectors typically have a lifespan of 5 to 7 years, though some newer models are designed to last 10 years, as indicated on their packaging. These newer units will emit a beeping sound to alert when they reach the end of their service life. For older models, homeowners need to be aware of when to replace them.

The sensor in a CO detector, like that in smoke detectors, has a limited lifespan. An old CO or smoke detector with new batteries might not provide effective protection if its sensor can no longer detect CO or smoke. When in doubt, it's safer to replace both CO and smoke detectors. Ensure you follow the installation and testing guidelines provided on the packaging of your CO and smoke detectors for your safety.

Commonly, when people "test" their CO and smoke detectors, they are merely checking the power source. Pressing the "test" button only confirms the unit has power, not its ability to detect high levels of carbon monoxide or smoke. To truly test these detectors, they need to be exposed to actual CO or smoke.

For professional help determining whether your home is armed and protected from carbon monoxide, contact a WIN Home Inspection expert near you today. You can also reach us at (800) 309-6753 or