Carbon Monoxide Safety Basics for Homeowners

Carbon monoxide (CO) is colorless, odorless, and gives you no warning until people start feeling sick. That’s why detectors exist—they are the only realistic way to catch CO before it becomes an emergency. The good news: CO safety is simple once you understand where CO comes from and where detectors actually belong.

If you want a wider checklist that includes both fire and CO basics across the whole house, you can pair this guide with the Home Fire Safety Checklist.

1. What Carbon Monoxide Is and Where It Comes From

CO is a byproduct of incomplete combustion. In a typical house, the main potential sources are:

• Furnaces and boilers that burn gas, oil, or propane
• Gas water heaters and gas dryers
• Fireplaces and wood stoves
• Gas ranges and ovens
• Portable generators and fuel-powered tools
• Vehicles idling in attached garages

In a normal, well-ventilated system, CO levels stay low. Problems show up when:

• Equipment is damaged, poorly maintained, or installed incorrectly
• Vents and flues are blocked, disconnected, or undersized
• Combustion happens in enclosed or semi-enclosed spaces (garages, basements, small rooms)

If you use multiple fuel-burning appliances, review the Heating Equipment Safety Checklist alongside this article and fix obvious issues before next season.

2. Symptoms of CO Exposure (So You Don’t Ignore Them)

CO exposure often gets mistaken for the flu or “feeling off.” Typical early symptoms:

• Headache
• Dizziness
• Nausea or vomiting
• Weakness or confusion
• Chest pain or shortness of breath

Red flag: symptoms improve when you leave the home and return when you’re inside again. That’s a strong sign you may have a CO problem and need detectors checked immediately.

3. Where CO Detectors Should Be Installed

CO detectors belong where people sleep and where CO is likely to accumulate—not buried in a random outlet.

• Outside each sleeping area: in the hallway near bedroom doors.
• On every level of the home: including the basement.
• Near, but not directly on, fuel-burning appliances: follow manufacturer clearance guidelines.
• In or near attached garages: use a detector in the entry path from the garage to the home.

If you are also updating smoke alarm layout, read the Smoke Detector Placement Guide so the two systems work together instead of leaving gaps.

4. Installation Height and Placement Mistakes to Avoid

Most modern CO detectors can be installed at wall outlet height or higher on the wall. The critical part is following the manual for your specific unit. General rules:

• Do not install directly next to fuel-burning appliances.
• Avoid putting detectors inside bathrooms or right outside steamy showers.
• Keep them away from constantly open windows or direct airflow from vents.
• Mount where you will actually hear the alarm from bedrooms.

If you have unusually high ceilings or open loft spaces, the Alarms for High-Ceiling Homes guide can help you decide how to cover those areas correctly.

5. Testing and Basic Maintenance

CO detectors are not “install and forget” devices. They need basic care:

• Press the test button at least once a month.
• Replace batteries at least once a year, or when the device chirps.
• Vacuum around vents to keep dust from clogging sensors.
• Replace the entire unit when it reaches its end-of-life date (often 7–10 years).

To keep everything on schedule, tie CO testing into your broader routine using the Alarm Testing Schedule.

6. What to Do If a CO Alarm Sounds

When a CO alarm goes off, treat it as real. Do not ignore it or “clear it and see if it happens again” while you stay inside.

1. Get everyone out of the building immediately.
2. Call emergency services from outside or from a neighbor’s house.
3. Do not re-enter the home until responders say it is safe.
4. Have a professional inspect and fix the source before resuming normal use.

This is also where a solid escape plan matters. If you haven’t set that up yet, use the Fire Escape Plan Checklist to build one route that works for both fire and CO emergencies.

7. Common Bad Habits That Create CO Risk

A few repeat offenders cause most residential CO incidents:

• Running vehicles in attached garages, even “just to warm up”
• Using grills or outdoor heaters inside garages or enclosed patios
• Running generators too close to the home, vents, or windows
• Skipping yearly service on furnaces, boilers, or fireplaces
• Ignoring “end-of-life” or trouble beeps from detectors

Fixing these habits is free and drops your CO risk fast.

8. Quick Carbon Monoxide Safety Checklist

• CO detectors installed on every level and outside each sleeping area
• Detectors tested monthly and batteries replaced on schedule
• All fuel-burning appliances serviced regularly
• No idling vehicles or fuel-burning tools in attached garages
• No grills, generators, or heaters used indoors or in enclosed spaces
• Clear plan for what to do if an alarm sounds

Carbon monoxide safety is not complicated. Install detectors correctly, maintain your equipment, kill a few bad habits—and you remove most of the real-world risk.