Carbon Monoxide: The Silent Killer

Carbon monoxide (also abbreviated “CO”) is an odorless, colorless gas that comes from fossil fuel burning (wood/pellet, natural gas, oil, propane, kerosene, coal, etc.) appliances. It can be produced when burning any fuel. Carbon monoxide (CO) and carbon dioxide (CO₂) are different. When you breath out, you are exhaling carbon dioxide (CO₂). Incidentally, plants inhale carbon dioxide and exhale oxygen.

If your home has a fireplace, a furnace, a non-electric water heater, a non-electric stove/oven, a boiler, etc., the occupants are potentially in danger of carbon monoxide poisoning. Even if your home has none of these appliances, but has an attached garage, there is still a potential carbon monoxide danger due to vehicle exhaust from the garage entering the home. Carbon monoxide exposure can injure or kill humans and animals. According to the Center for Disease Control (CDC), “Each year, more than 400 Americans die from unintentional CO poisoning not linked to fires, more than 20,000 visit the emergency room, and more than 4,000 are hospitalized.” Other resources put these annual numbers much higher. According to the Environmental Protection Agency (EPA), carbon monoxide (CO) is the most common cause of poisoning death in the US. CO poisoning is a real issue that everyone needs to be familiar with and should be able to recognize the symptoms.

Keep in mind that the detection of or testing for carbon monoxide (CO) is well outside the scope of a home inspection. The Standard of Practice of ASHI (the American Society of Home Inspectors), however, requires home inspectors to report on the presence or absence of installed carbon monoxide (CO) detectors and smoke detectors as part of a home inspection. If possible, I try to determine the year of manufacturer of installed CO and smoke detectors and I recommend older units be replaced. In my home inspection travels, I regularly find smoke and carbon monoxide detectors that are very old and should have been placed years (and sometimes decades) ago.

Carbon monoxide poisoning mimics many of the same symptoms of the flu: dizziness, nausea, headache, fatigue, vomiting, confusion, etc. The warning signs can be very slow to be noticed which is one of the dangers. A loss of consciousness indicates a severe exposure (high concentration) to CO. If you are sleeping and are poisoned by CO, you may never wake up. The complications of CO exposure can lead to brain damage, heart damage, or death.

Carbon monoxide (CO) is a health hazard because, once it’s inhaled, it combines with the oxygen carrying hemoglobin in the blood to form carboxyhemoglobin (COHb). Your red blood cells have an easier time carrying carbon monoxide than oxygen, so exposure to CO makes the oxygen levels in your bloodstream diminish. This prevents needed oxygen from getting to your body’s organs, such as your brain. If multiple members or pets in your home are exhibiting flu-like symptoms (such as nausea, shortness of breath, headache, and/or weakness), this is a clue that carbon monoxide poisoning may be the culprit. Exposure to CO can also cause death. Get outside to fresh air immediately and call 911. The fire department is prepared to determine the cause/source of the issue. The cause of the CO problem needs to be repaired before anyone can safely go back into the home.

How Do I Protect My Family?

All homes should have, at least, one carbon monoxide (CO) detector installed. The 2018 IRC (International Residential Code) requires CO detectors to be installed outside sleeping areas (the code uses the term “sleeping areas” for bedroom). The code requirement goes back many years. CO detectors (like smoke detectors) should never be installed near ceiling fans, near peaks on cathedral ceilings or near exterior doors or windows since these can prevent the detector from properly detecting dangerous exhaust gases in the air. Older CO detectors generally need to be replaced every 5~7 years, although most newer CO detectors being manufactured today have a 10 year life expectancy. This information would be clearly noted on the unit’s packaging. When these newer units have reached 10 years of service life, they will beep to indicate that it is time to replace them. For older units, it is up to the homeowner to know when to replace them.

The sensor inside the CO detector (just like smoke detectors) has a relatively short life span; an old CO or smoke detector with brand new batteries likely won’t provide any useful protection if the sensor can no longer detect CO or smoke. If in doubt, replace your home’s CO and smoke detectors to be safe. Follow the instructions on your CO and smoke detector’s packaging regarding installation locations, testing procedures, when to replace, etc.

When most people think they are “testing” their CO and smoke detectors, they are actually only testing the unit’s power source. In other words, pressing the “test” button only confirms that the unit is powered, not that it will necessarily detect high levels of carbon monoxide or smoke in your home. You would need a source of CO near the detector to actually test it for its function. The same goes for smoke detectors. You would really only know if your smoke detector “works” by putting a source of smoke near its sensor and awaiting for the alarm to go off. Smoke and CO detectors have a small amount of a radioactive element inside that decays naturally over time. When the interior sensor is no longer good, the detector is just a piece of plastic and metal with no helpful function.

Carbon monoxide exposure is generally measured in terms of parts per million (aka ppm). Parts per million (or PPM) is a unit of measure. A CO exposure to 35 ppm over 8 hours is the maximum exposure allowed by OSHA (Occupational Safety and Health Administration). Just 2 hours of exposure to CO at 200 ppm can lead to fatigue, headaches, nausea, and dizziness. 2 hours of CO exposure at 800 ppm can lead to unconsciousness or death. Over 1,000 ppm CO exposure for 20 minutes or less can lead to death. As you can see, it is critical that if you are exposed to carbon monoxide that you act quickly.

Carbon monoxide detectors won’t alarm immediately if detecting CO. Industry standards require that they must alarm within 60~240 minutes when a carbon monoxide concentration of 70 ppm is detected. They must alarm within 10~50 minutes when a concentration of 150 ppm is detected, and within 4~15 minutes when a concentration of 400 ppm is detected.

The below photos show plug-in style and wall/ceiling mounted carbon monoxide (CO) detectors.

Keep in mind that the detection or testing for carbon monoxide is outside the scope and standard of practice of a home inspection. However, a home inspection should include reporting on the presence or absence of a carbon monoxide detector(s) in the inspected property. If no CO alarm is found within the home, or if an installed unit is more than 7 years old, installing a new carbon monoxide detector(s) is always recommended.

How Do I Help Prevent CO Poisoning?

First, as noted above, installed CO detectors in your home and replace them as needed. Next, make sure that all fossil fuel burning appliances are professionally and properly installed and regularly maintained. Furnaces, non-electric water heaters, and boilers should be serviced annually by a qualified HVAC professional or licensed plumber. Doing this helps ensure these appliances are installed and operating properly and are safe to use.

Fireplaces, furnaces, boilers, non-electric water heaters, etc. need to vent their exhaust gases into a chimney or be direct-vented to the exterior. If any of these appliances vents into a chimney, the chimney should be professionally cleaned/inspected annually. From my experience, most homeowners never have their chimneys cleaned as they don’t think this maintenance is needed. Leaves, debris, and animal nests can block a chimney and force the appliances’ exhaust gases to backup into the home. This is a common cause of CO injuries and deaths. Once your chimney has been professionally cleaned/inspected, a rain cap should be installed on top to prevent future leaves/debris and animals from entering and potentially blocking your chimney.

Vent-free gas and propane (LP) fireplaces do exist; I run across them from time to time in my home inspection travels. These units don’t have an exhaust vent (no connection into a chimney) and are designed to fully burn the fuel. These units have an oxygen depletion sensor which is supposed to detect if the room’s air lacks oxygen due to high CO levels. I’ve heard of instances of these sensors failing, so I don’t recommend vent-free appliances inside the home. Some states forbid vent-free fireplaces altogether. Vent-free appliance manuals tell the user to open a window in the room that the appliance is located to ensure sufficient combustion air, although virtually no home owners read or heed this warning.

Next, never operate things like generators or grills inside the home, basement, or garage. They need to be used outside in a well-ventilated area. Also, only operate vehicles in a garage with the garage door fully open. Never use a gas or LP stove/oven to heat your home.

If you have a fireplace, ensure that the damper is open before starting the fireplace. If the fireplace is gas or LP and has a running pilot light and your fireplace has a damper, a special clip should be installed to ensure that the damper can not be fully closed. Carbon monoxide can fill your home simply due to a running pilot light with no ventilation (closed fireplace damper). Cleaning solvents (such as paint thinner) should only be mixed or used outdoors as they can also produce CO in some cases.

Ensuring that your furnace, water heater, etc. have sufficient combustion air is critical. I find many home owners finish their basements without permits and then wall around the portion of the basement where a furnace and/or non-electric water heater are located. These appliances need sufficient oxygen to properly and safely operate. Modern building standards stipulate the minimum size of a room where fossil fuel appliances are installed and how much fresh air the room must have. This sizing is based upon the type and BTU ratings of the appliances in the room. Over many years inspecting homes, I’ve seen numerous instances of homeowners tightly closing off furnaces and water heaters with drywall and then also storing things like boxes, paint cans, and other combustible items in these small rooms. If the stored items don’t starve the appliances for oxygen, they can readily catch fire if a fossil-fuel burning appliance were to malfunction. If finishing a basement, start by getting a permit, as this is generally required in almost all cases nowadays in our area. Then ensure the utility room (where the furnace, water heater, etc. are located) is large enough to ensure proper appliance operation and combustion air, that this room’s walls have proper upper and lower vents to ensure needed air flow, and don’t stored items near the appliances.

Attached garages are required to have fire-separation (also commonly called a ‘firewall’). Properly installed mudded and taped drywall should separate the garage from living spaces and attics. One purpose of the fire-separation is to help slow a garage fire’s quick spread into the home, but another is to help prevent garage carbon monoxide from entering living space. Any place where wiring, ductwork, or plumbing penetrates garage walls or ceilings, these areas should be properly sealed. There should be no heating registers in the garage since a fire or carbon monoxide can readily get into living space via the ductwork, even if the register is closed.

Pulldown ladders should not be installed in attached garages as they compromise the fire-separation and are not air tight to the garage attic space. If there is an access panel to a garage attic, the panel cover should also be a fire-rated material, such as drywall. Plywood, OSB, particle board, etc. are not fire-rated and will burn in the event of a garage fire. Some areas of the country even require self-closing garage mandoors into living space; this prevents a door from the garage from being accidentally left open where a fire or carbon monoxide can enter the home. To my knowledge, no cities or townships in our area require self-closing garage mandoors, however.

Preventing carbon monoxide poisoning is fairly easy to do when home owners use common sense and have, at least, one CO detector in their home. There are still many people unfamiliar with the risks, the symptoms, and the causes, however. As you can see, it is critical that if you are exposed to carbon monoxide that you act quickly. This means moving to fresh exterior air and calling 911. Minutes can be the difference.

Also, read my related smoke detector article.

Matthew Steger is a Certified Level 1 Infrared Thermographer, an ASHI Certified Inspector (ACI), and an electrical engineer. He can be reached at matthew@thehomeinspectorsnotebook.com. No article, or portion thereof, may be reproduced or copied without prior written consent of Matthew Steger.