Carbon monoxide (CO) is often called the silent killer because it is odorless, tasteless, and invisible, making this toxic gas one of the most overlooked dangers in homes. The Centers for Disease Control and Prevention estimates that about 450 people die and 20,000 people are admitted to the emergency room each year as a result of unintentional carbon monoxide poisoning. Both numbers spike during winter months when heating systems are working overtime. To keep you and your family safe, understand the many sources of carbon monoxide in your home, as well as ways to test for carbon monoxide.
Carbon monoxide (CO) poisons humans and other living animals by being absorbed into the bloodstream, where it replaces the oxygen in red blood cells. The result can be severe tissue damage or death. For this reason, CO levels in the home are a very serious issue. Symptoms of carbon monoxide poisoning can be similar to symptoms for influenza and other illnesses, which is why CO poisoning so often goes undetected. Symptoms can include:
- Dull headache
- Nausea or vomiting
- Shortness of breath
- Blurred vision
- Loss of consciousness
A number of signs distinguish carbon monoxide poisoning from the flu. For example, if everyone in the home—including pets—are sick at the same time, carbon monoxide should be considered as the culprit. And if you feel better when leaving the house, it's a signal that the problem may be CO gas. While everyone is prone to carbon monoxide poisoning, infants, the elderly, and those with heart disease, anemia, and breathing problems are more likely to get sick.
Sources of Carbon Monoxide in the Home
Carbon monoxide is produced by gas, oil, coal, charcoal, and wood fuels that have burned incompletely. Carbon monoxide is more common among older furnaces, as well as in HVAC systems and gas water heaters that have not been properly vented. Electric furnaces, electric water heaters, electric ovens, and all other electrically powered devices operating normally do not produce carbon monoxide.
While artificial heating is by no means the only source of carbon monoxide in the home, it is a major contributor. Besides carbon monoxide gas being produced by furnaces improperly installed or vented, it can come from other fuel-fired sources, including but not limited to:
- Gas ranges and stoves
- Gas clothes dryers
- Gas water heaters
- Portable fuel-burning space heaters
- Wood-burning stoves
- Vehicles running in an attached garage
- Charcoal/gas grilles
As a guard against CO poisoning, safety-conscious homeowners may want to own a portable carbon monoxide meter. This is a much different tool that the inexpensive CO detectors that attach to the wall. A CO meter is a portable measuring tool that allows you to pinpoint the source of CO gas in whatever room it originates, providing an accurate measurement of how much gas is present. All portable carbon monoxide meters work differently, so consult manufacturer instructions for details about your own meter.
Equipment / Tools
- Portable carbon monoxide meter
If you and your family are experiencing physical symptoms and suspect the presence of dangerous levels of carbon monoxide in your home, leave the home immediately and call the fire department or a professional on-site air testing company. Open all of the windows and doors and turn off all stoves, your HVAC system, and the water heater.
Prepare the Meter
Turn on the meter with the "ON" button. Let the meter fully power up. Your portable carbon monoxide meter will have some type of zero-point setting to establish a base point. Do this outdoors or in a room that you know is free of carbon monoxide.
Before using the meter, run the diagnostic self-test to calibrate the meter, as directed by the manufacturer's instructions. It may take from three to five minutes to complete the test.
Test the Area of Suspected Carbon Monoxide
Go to the area that you believe has carbon monoxide and run the meter until it reaches at least a 90-percent reading (in many models).
Check the Meter Readings
Carbon monoxide meters will report back to you in various ways: with sounds, lights, or on-screen readings. A 0-1 PPM (parts per million) reading is considered to be a normal background level, with 35 PPM being the OSHA/NIOSH maximum 8-hour exposure limit. If your reading exceeds the normal background level reading, you should consult a service person to inspect the suspect appliance.
Alternative Methods of Testing for Carbon Monoxide Gas
Indoor Air Quality Test
The ultimate and most accurate way to detect the presence of carbon monoxide in the home is with an indoor air quality test. Private companies specialize in performing indoor air quality and improvement tests that include carbon monoxide testing. Some municipal fire departments and utility companies will come to your home and check for carbon monoxide for free or at reduced rates.
The main tool used in these tests is an electronic portable toxic multi-gas monitor. This device differs from the consumer-level carbon monoxide detectors in that it can be calibrated to detect trace carbon monoxide gas from nearly 0 PPM and at increments as small as 1 PPM. In addition to testing for carbon monoxide, most of the private companies will test for other harmful pollutants, such as mold, allergens, radon, formaldehyde, and more.
HVAC Combustion Analysis
If you or the testing company believe that the HVAC system is the source of the carbon monoxide, you can contract with an HVAC company to check your system with a combustion analyzer. A combustion analyzer is an electronic device that tests vented gases coming directly from furnaces to ensure that the ratio of carbon monoxide to oxygen remains within a safe range. A combustion analyzer tests only gases combusted directly from a furnace, not overall air quality. The device tends to be too expensive and limited in use for most do-it-yourselfers to purchase. Many HVAC companies and on-site air quality testing companies do not own combustion analyzers, so check with the company in advance before they come to your house.
Consumer-Level Carbon Monoxide Gas Detectors
The easiest way to see if there is carbon monoxide inside your home is with a carbon monoxide detector (this tool is different from a carbon monoxide meter). In fact, many building codes require a carbon monoxide gas detector. If you do not have carbon monoxide gas detectors in your home, not only are you putting you and your family at risk, but an inspector could also flag you and prevent the sale of your home or condo.
Such off-the-shelf carbon monoxide gas detectors are valuable, but they should be viewed only as passive carbon monoxide detectors. They are not as accurate as portable toxic multi-gas monitors or portable carbon monoxide meters since they typically measure only down to 30 PPM. The aim of these carbon monoxide gas detectors, too, is to act as the last layer of warning to protect individuals in habitable areas such as bedrooms, dining rooms, living areas, and hallways. These carbon monoxide gas detectors are not meant to detect carbon monoxide gas at suspected locations of origins, such as furnace rooms or even in kitchens. In fact, most of these carbon monoxide gas detectors should be installed beyond a radius specified by the detectors' instructions: 5 feet or more beyond cooking appliances and 20 feet or more beyond furnaces, for example.