Is Carbon Monoxide (CO) in Your Home? Here's How to Know for Sure
✓ Your concern is understandable. Carbon Monoxide (CO) is classified as a critical health risk — testing is the only way to confirm your exposure level.
You're not overreacting. Carbon Monoxide (CO) is invisible and odorless — the EPA recommends every homeowner test for it regardless of age or condition of the home.
The test kit below can tell you in 48 hours whether your home has elevated levels. Testing is the only way to know for sure.
Carbon Monoxide (CO) is a critical-severity indoor air quality hazard that the EPA classifies as requiring immediate action. It is most commonly found in kitchen, garage, basement and originates from gas stoves, furnaces, water heaters.
CO is a silent killer — colorless, odorless, and lethal at high concentrations. It binds to hemoglobin 200x more than oxygen. Every home with fuel-burning appliances needs a CO detector.
Your family may be breathing carbon monoxide (co) right now.
Kidde Carbon Monoxide Detector
This test kit gives you results in 48 hours. Testing is recommended by the EPA as the first step for any suspected hazard.
Compare options →Prefer a free assessment first? Take the Air Quality Risk Score Quiz →
Symptoms to Watch For
If you or your family members are experiencing any of these, carbon monoxide (co) could be the cause:
Quick Reference Data
| Hazard | Carbon Monoxide (CO) |
| EPA Severity | CRITICAL |
| Common Sources | gas stoves, furnaces, water heaters, fireplaces, cars in attached garages, portable generators |
| Affected Areas | kitchen, garage, basement, laundry, bedroom, dining-room, hallway, workshop, utility-room, crawl-space, attic, sunroom, mudroom, home-office, nursery |
| Health Symptoms | headache, dizziness, nausea, confusion, shortness of breath, blurred vision, loss of consciousness |
| EPA Recommendation | Install CO detectors on every level of your home and outside sleeping areas. Never run generators indoors. Have fuel-burning appliances inspected annually. If alarm sounds, evacuate immediately and call 911. |
Your Children Breathe 20,000 Liters of This Air Every Day
Kids breathe more air per pound of body weight than adults. Their lungs are still developing. If carbon monoxide (co) is in your home, they're getting a higher dose than you are. You childproof cabinets and plug outlets — but have you checked what they're breathing?
⚠️ The EPA estimates indoor air can be 2–5× more polluted than outdoor air. Your family breathes 20,000 liters of indoor air every day.
If carbon monoxide (co) is present, every breath could be doing damage you can't see or feel — until it's too late.
Where It Hides in Your Home
Common Sources
- • gas stoves
- • furnaces
- • water heaters
- • fireplaces
- • cars in attached garages
- • portable generators
What the EPA Recommends
EPA-Recommended Actions
Install CO detectors on every level of your home and outside sleeping areas. Never run generators indoors. Have fuel-burning appliances inspected annually. If alarm sounds, evacuate immediately and call 911.
Sources & Citations
- 📎 EPA — Carbon Monoxide (epa.gov)
- 📎 CDC — CO Poisoning (cdc.gov)
- 📎 EPA — Indoor Air Quality (general)
All data on this page is based on publicly available information from the cited sources. This page is not endorsed by the EPA, CDC, or WHO.
📋 Our Testing Methodology
Hazard severity classifications follow the EPA's Indoor Air Quality assessment framework:
- • Critical: Immediate health risk — evacuate and contact emergency services
- • High: Chronic exposure risk — test within 1 week, remediate within 30 days
- • Moderate: Potential risk — test to confirm, address if confirmed
Product recommendations are based on published detection accuracy, third-party test results, and EPA-recommended testing methods. Updated November 2026.
Test Kits & Protection
EPA recommends testing as the first step for any suspected carbon monoxide (co) exposure. These are the tools most homeowners start with.
Kidde Carbon Monoxide Detector
Plug-in CO alarm with battery backup. Digital display. Peak level memory.
First Alert Smoke and CO Alarm
Combined smoke and carbon monoxide detector. 10-year sealed battery.
Airthings 2960 View Plus Air Quality Monitor
Tracks radon, CO2, VOC, PM2.5, humidity, temp, pressure. Wi-Fi connected. Battery powered. Free app.
Guidance sourced from EPA, CDC, and Health Canada publications.
Your Home Air Defense Kit
These 3 items help you monitor and improve your indoor air.
LEVOIT Core 300-P HEPA Air Purifier
A true HEPA filter captures 99.97% of airborne particles — dust, pollen, mold spores, and pet dander. Running one in your main living space is the single most effective step you can take for cleaner indoor air.
Get the Air Purifier — Breathe Cleaner at Home → First Alert Radon Gas Test Kit
Radon is the second leading cause of lung cancer and you can't smell or see it. This EPA-listed test kit gives you results in days — know your levels before it becomes a problem you can't undo.
Test for Radon — What You Don't Know Can Hurt You → Digital Moisture Meter
Hidden moisture behind walls and under floors is how mold problems start. A pin-type moisture meter lets you catch elevated readings early — before you see or smell the damage.
Get the Moisture Meter — Stop Mold Before It Starts →Your home may have hidden hazards you can't see, smell, or taste.
Our Room-by-Room Scanner checks every corner of your home for 20+ air quality hazards.
Scan My Home Now →One more thing — your home may have related hazards
If your home has carbon monoxide (co), there's a chance it also has gas stove emissions (no2 and benzene). Both can thrive in the same conditions. When you test for one, check for the others too.
Related Hazards
Gas Stove Emissions (NO2 and Benzene)
Gas stoves release nitrogen dioxide and benzene even when turned off. A 2022 study linked gas stoves to 1 in 8 childhood asthma cases. Benzene is a known carcinogen that spreads throughout the home.
Attached Garage Air Contamination
Car exhaust, gasoline vapors, and stored chemicals from attached garages seep into living spaces. A running car in an attached garage raises CO levels in the home within minutes, even with the garage door open.
Radon Gas
Radon is the #2 cause of lung cancer after smoking. It seeps from soil into basements and crawl spaces. You cannot see, smell, or taste it. The only way to know is to test.
Nitrogen Dioxide (NO2)
Gas produced by gas stoves and heaters. Causes airway inflammation at elevated levels. NO2 irritates the respiratory tract and worsens asthma. Children and elderly are most vulnerable. Even short-term exposure at moderate levels can trigger symptoms.
How Carbon Monoxide (CO) Compares to Related Hazards
Carbon Monoxide (CO) is classified as CRITICAL — the highest severity tier for indoor air hazards. Of the 4 related hazards we track, 3 carry a lower severity rating. This means carbon monoxide (co) should be your top testing priority if you suspect any indoor air quality issue.
Carbon Monoxide (CO) poses a higher immediate risk than Gas Stove Emissions (NO2 and Benzene). While both require attention, carbon monoxide (co) is classified as critical severity versus gas stove emissions (no2 and benzene)'s high rating. If you test for one, the EPA recommends testing for the other simultaneously — they share common areas like kitchen, bedroom, dining room.
Shared locations: kitchen, bedroom, dining room, hallway, nursery
Common causes: gas stoves
Carbon Monoxide (CO) poses a higher immediate risk than Attached Garage Air Contamination. While both require attention, carbon monoxide (co) is classified as critical severity versus attached garage air contamination's high rating. If you test for one, the EPA recommends testing for the other simultaneously — they share common areas like garage, kitchen, bedroom.
Shared locations: garage, kitchen, bedroom, basement, mudroom, hallway, laundry, nursery, utility room, attic
Both Carbon Monoxide (CO) and Radon Gas carry the same critical severity classification. Their combined presence in your home creates a compounding effect that exceeds the risk of either alone. Both are commonly found in basement, crawl space, bedroom. Addressing one without testing for the other leaves a blind spot in your home's air quality.
Shared locations: basement, crawl space, bedroom, dining room, utility room, sunroom, laundry, home office, garage
Carbon Monoxide (CO) poses a higher immediate risk than Nitrogen Dioxide (NO2). While both require attention, carbon monoxide (co) is classified as critical severity versus nitrogen dioxide (no2)'s moderate rating. If you test for one, the EPA recommends testing for the other simultaneously — they share common areas like kitchen, basement, bedroom.
Shared locations: kitchen, basement, bedroom, garage, dining room, hallway, nursery, utility room, laundry, workshop
Common causes: fireplaces
Severity classifications follow EPA Indoor Air Quality assessment standards. Related hazards share environmental conditions but may require different testing methods.
What Your Carbon Monoxide (CO) Test Results Mean
After testing for carbon monoxide (co), you'll receive a measurement or a positive/negative result. Here's how to interpret what that number means for your home and family.
No Detection / Clear
No carbon monoxide (co) was detected in your test. Your home is currently clear of this specific hazard.
What to do: Re-test annually or after any renovation, water damage, or structural change. Carbon Monoxide (CO) can appear at any time due to gas stoves or furnaces.
Trace Detection
Trace amounts of carbon monoxide (co) were found. Even at low levels, a critical-severity hazard like this warrants prompt investigation of gas stoves, furnaces, water heaters.
What to do: Locate and eliminate the source immediately. Install CO detectors on every level of your home and outside sleeping areas. If you cannot identify the source, contact a licensed professional.
Elevated / At Action Level
Your test shows elevated carbon monoxide (co) at or above the EPA action level. At this concentration, the health risk is significant and immediate steps are required.
What to do: Do not delay. Install CO detectors on every level of your home and outside sleeping areas. Contact a licensed remediation professional within 24 hours. Evacuate if you experience headache or dizziness.
Interpretation guidelines are based on EPA standards for chemical hazards. For carbon monoxide (co), install co detectors on every level of your home and outside sleeping areas. Always confirm results with a certified professional.
Carbon Monoxide (CO) Exposure Limits & Key Numbers
Published reference values from EPA, WHO, CPSC, OSHA and CDC — the same numbers professionals use to interpret a test result.
CO concentration and symptom timeline (healthy adults)
| CO (ppm) | Effect | Time to symptoms |
|---|---|---|
| 0–10 | Normal indoor background | None |
| 50 | OSHA 8-hour workplace limit — no symptoms in healthy adults | None at rest |
| 200 | Mild headache | Within 2–3 hours |
| 400 | Headache; life-threatening with continued exposure | Within 1–2 hours; fatal after ~3 hours |
| 800 | Dizziness, nausea, convulsions | Within 45 minutes; fatal within 2–3 hours |
| 1,600 | Headache, rapid heart rate, dizziness | Within 20 minutes; fatal within 2 hours |
| 3,200 | Severe symptoms | Within 5–10 minutes; fatal within about 1 hour |
| 6,400 | Severe symptoms | Fatal within 10–15 minutes |
| 12,800 | Immediate unconsciousness | Fatal within 1–3 minutes |
Figures compiled from CPSC and OSHA guidance for healthy adults; people with heart disease, children, and pregnant women are affected faster and at lower concentrations.
UL 2034 residential CO alarm response requirements
| CO concentration | Alarm must sound within |
|---|---|
| 70 ppm | 60–240 minutes |
| 150 ppm | 10–50 minutes |
| 400 ppm | 4–15 minutes |
Residential alarms deliberately ignore short bursts below 70 ppm to avoid nuisance trips — so a headache at 100 ppm can arrive before your alarm ever sounds. That is why placement (every level, outside sleeping areas) matters as much as the alarm itself.
Reference tables compiled from EPA — Carbon Monoxide; CDC — CO Poisoning and the agency guidelines cited above.
Questions Homeowners Ask About Carbon Monoxide (CO)
What are the symptoms of carbon monoxide (co)?
Common symptoms of carbon monoxide (co) include: headache, dizziness, nausea, confusion, shortness of breath, blurred vision, loss of consciousness. If you are experiencing these symptoms, test your home and consult a healthcare provider.
How do I test my home for carbon monoxide (co)?
Common sources include: gas stoves, furnaces, water heaters, fireplaces, cars in attached garages, portable generators. You can test using the products recommended above. Install CO detectors on every level of your home and outside sleeping areas. Never run generators indoors. Have fuel-burning appliances inspected annually. If alarm sounds, evacuate immediately and call 911.
Is carbon monoxide (co) dangerous to children?
Yes. Children are especially vulnerable to carbon monoxide (co) because their respiratory systems are still developing and they breathe more air per pound of body weight than adults. CO is a silent killer — colorless, odorless, and lethal at high concentrations. It binds to hemoglobin 200x more than oxygen. Every home with fuel-burning appliances needs a CO detector.
At what CO level does a carbon monoxide alarm go off?
Under UL 2034, a residential alarm must sound within 60–240 minutes at 70 ppm, within 10–50 minutes at 150 ppm, and within 4–15 minutes at 400 ppm. Lower sustained levels may never trigger the alarm, which is why symptoms matter too — if the whole household has headaches that clear when you leave, treat it as CO until proven otherwise.
What is a safe CO level inside a home?
Zero is the goal — CO should not be present at all in a well-functioning home. WHO indoor guidelines allow up to about 9 ppm averaged over 8 hours and 6 ppm over 24 hours. Any sustained reading above ~25 ppm on a monitor means find the source now; readings in the hundreds mean evacuate and call 911.
Can you get carbon monoxide poisoning in an all-electric house?
It is less likely but not impossible. CO comes from burning fuel, so the main all-electric-house risks are a car running in an attached garage, a portable generator used near the home, a wood-burning fireplace with a blocked flue, or exhaust back-drafting from an attached neighbor's unit. Detectors are still recommended.
Stop wondering.
Start knowing.
The data is clear. The next step is testing.
The EPA notes that carbon monoxide (co) can only be confirmed through testing — it's often invisible and odorless. A test kit or monitor gives you a real number instead of a guess.
1 in 15 US homes has elevated radon levels — the only way to know is to test.
Take the free Air Quality Risk Score quiz and find out what's lurking in your home.
Medical & Environmental Disclaimer
This information is for educational purposes and is based on EPA and CDC guidelines. It is not a substitute for professional environmental testing, medical advice, or remediation services. If you suspect a gas leak or carbon monoxide emergency, evacuate immediately and call 911.
Maren K. Solberg
Residential Air Quality Researcher · 10+ Years Investigating Home Environmental Hazards
Garrison F. Hale has spent over a decade researching residential air quality hazards, including mold, VOCs, radon, and combustion byproducts. He translates complex EPA and CDC guidance into clear, actionable steps for homeowners.
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