When and Where to Install Carbon Monoxide Detectors

Carbon Monoxide Detector
Jeffrey Coolidge / Getty Images

When should you get carbon monoxide (CO) detectors for your home? Does every home need one? What kind of appliances can cause carbon monoxide poisoning?

The short answer to all of these questions is: When you are burning any type of liquid or solid fuel for heating, cooking, or other uses, you should have CO detectors installed in your home. And because cars and other gas-powered equipment create carbon monoxide, virtually every home should have a CO detector, even if there are no fuel-burning appliances in the house.


This poisonous gas is odorless, colorless, and tasteless, which is what makes it so dangerous. The health concerns occur because when CO enters your lungs, it binds to the hemoglobin of red blood cells, taking the place of oxygen. This leads to oxygen starvation (hypoxia) of the blood cells.

About Carbon Monoxide​

Carbon monoxide is a gas that is present in the air, but it's the presence of high levels—such as those emitted by burning fuel—that can make this gas deadly. Carbon monoxide is a pollutant formed by the combustion of hydrocarbon fuels, including natural gas, propane, wood, coal, and gasoline, among others. All combustion appliances and equipment around the home produce CO gas, no matter how energy-efficient they are.

CO is measured in parts per million, or ppm. Symptoms of CO exposure worsen with longer and higher exposure:

  • 0.5 to 5 ppm: Normal level of CO for homes with combustion appliances.
  • Below 70 ppm: Exposure for 6 to 8 hours can lead to symptoms including headaches and dizziness. People with heart conditions may feel additional symptoms, such as chest pain.
  • 100 ppm: Exposure for two hours or more can cause a headache, fatigue, and nausea.
  • 150 to 200 ppm: Long-term exposure can lead to death.

Types of Fuel-Burning Appliances

Fuel-burning appliances that are properly tested, installed, and maintained are generally safe to use, but in the event of a clogged exhaust vent or any part of the appliance failing, hazardous levels of carbon monoxide can be released into the home. Many CO home hazards have occurred simply from animals' nests or heavy snowfall blocking appliance vents or chimneys. Common types of combustion appliances used in homes include:

  • Wood-burning appliances, including wood stoves, heat stoves, fireplaces, wood-pellet stoves, and box or parlor stoves
  • Oil, propane, or natural gas appliances, including boilers, furnaces, cooktops and ranges, some refrigerators, hot water heaters, space heaters, and fireplaces or hearth products
  • Gas or diesel fuel equipment, such as generators (these should always be used outdoors)
  • Bio, agricultural, or other fuel-burning types of heating stoves

How Many CO Detectors Do I Need?

Recommendations for CO detectors are similar to those for smoke alarms. As a minimum, each home should have one CO detector on each floor, one in or just outside each sleeping area, and one in the basement. In homes where multiple bedrooms adjoin a common hallway, a single detector in the hallway can provide protection for all of the rooms. However, if the home has forced-air heat (with a conventional gas or propane furnace), carbon monoxide leaking in the furnace system can reach each room individually. Therefore, it's safest to include a separate CO detector in each bedroom or other sleeping areas.

If other areas of the home, such as an attic or closed-in porch or sunroom, have combustion appliances or are used as sleeping areas, each of those spaces should have a CO detector. The same is true for a garage or outbuilding (greenhouse, garden shed, etc.) with a non-electric heater.

Types of Carbon Monoxide Detectors

CO detectors are available in plug-in and hard-wired models. There are also combination detectors that provide detection for both fire and carbon monoxide. Hard-wired detectors are connected to a home's wiring system and should include batteries for backup power so they keep working if the power goes out. Plug-in detectors simply plug into any standard electrical outlet and always include battery backup.

Most hard-wired detectors are interconnected so that if one detector is triggered all of the other detectors in the house are automatically triggered and sound their alarms. Interconnection capability is available on some plug-in detectors, which interconnect through wireless technology.

While standard CO detectors have basic digital readouts or lights indicating various alarm functions or low-battery conditions, CO detectors with a digital carbon monoxide display include a readout of carbon monoxide levels (in ppm) at all times. This can help with early detection of problems with combustion appliances (such as a leaky furnace or poorly vented hot water heater) and can alert you to higher-than-normal CO levels, particularly levels that lead to symptoms but are not high enough to trigger an alarm.

Installation Tips and Maintenance

Anyone can install plug-in CO detectors; you simply put in a fresh battery and plug the unit into any outlet that is not covered by furniture, drapes, or other obstructions. Homeowners with electrical experience can easily install hard-wired detectors; otherwise, an electrician is the best pro for the job.

Always follow the manufacturer's installation requirements and recommendations. Some CO detectors work best at levels below 5 feet above the floor; others (such as combination units) must be installed on or near the ceiling. In addition, there are a few general locations to avoid:

  • High-humidity areas, such as bathrooms or saunas
  • Areas with temperatures below 40 degrees F or above 100 degrees F
  • Near heating/cooling vents, ceiling fans, open windows, or other areas with strong or turbulent airflow or heavy ventilation
  • Closer than 5 feet from cooking appliances or within 20 feet of combustion appliances.
  • In direct sunlight or outdoors


Maintain your CO detectors by cleaning them monthly with a vacuum and soft brush attachment. Replace the battery in each unit every six months. Replace the detector units as recommended by the manufacturer; the units don't last forever. To keep track of how old your detectors are, write the purchase date on the back of each unit before installing it. You will see this date every time you change the battery, so you can replace units before they hit their expiration date.