Carbon Monoxide vs Carbon Dioxide
You see a "CO2 monitor" listed online and wonder — would it protect your family from carbon monoxide? Or a news report mentions "carbon dioxide poisoning" and you're not sure if that's the same thing your CO alarm detects. The names carbon monoxide (CO) and carbon dioxide (CO2) look almost identical, but the gases are not interchangeable — and neither are the detectors. CO is a toxic poison gas produced by incomplete combustion in furnaces, generators, stoves, and cars. CO2 is a normal part of the air we exhale, typically a ventilation concern at home and an acute hazard mainly at very high concentrations in industrial or confined-space scenarios. This guide explains the key differences, symptoms, sources, and which detector you actually need.
This is general safety information — not medical advice. If you suspect active CO exposure or severe symptoms, move to fresh air and contact emergency services.
Key Takeaways
- CO (carbon monoxide): a true poisoning risk at relatively low concentrations. A CO alarm sounding should be treated as an emergency.
- CO2 (carbon dioxide): usually a ventilation/indoor-air-quality indicator in homes; becomes an acute hazard mainly in unusual high-concentration scenarios.
- Detectors: a CO alarm detects CO. A CO2 monitor measures CO2 for ventilation awareness. They are not interchangeable.
- If a CO alarm sounds, leave immediately and call emergency services — a CO2 monitor will not warn you about CO.
CO vs CO2: Side-by-Side Comparison
| Feature | Carbon Monoxide (CO) | Carbon Dioxide (CO2) |
|---|---|---|
| What it is | Poison gas from incomplete combustion | Gas naturally present in air; produced by breathing and combustion; used widely in industry |
| Can you smell it? | No (odorless, colorless) | No (odorless, colorless) |
| How it harms you | Prevents the body from using oxygen normally (poisoning) | At high levels, displaces oxygen and affects breathing/acid-base balance |
| Typical "home" scenario | Equipment failure or exhaust trapped indoors (furnace, generator, car in garage) | Most often "stuffy air" from low ventilation, not an actual "leak" |
| What to install | UL-listed CO alarms in recommended locations | Optional CO2 monitor for ventilation awareness (not a safety alarm for CO) |
| Urgency | High: CO alarm or symptoms → leave immediately and get help | Usually low at home; high urgency mainly for industrial/confined-space releases |
Where Each Gas Comes From
Carbon monoxide (CO): incomplete combustion
CO forms when fuels do not burn completely. Common CO sources include malfunctioning furnaces/boilers, blocked chimneys or flues, gas stoves used improperly, generators, fireplaces, and vehicle exhaust in enclosed or attached garages. Because CO is invisible and odorless, you often cannot "notice" it until symptoms appear — which is why working CO alarms and basic maintenance matter.
Carbon dioxide (CO2): breathing, combustion, and industrial use
CO2 is produced by people and pets (exhaled breath) and by combustion. Indoors, CO2 is often used as a practical signal of ventilation: higher readings usually mean more occupants and/or less fresh-air exchange. A true high-CO2 emergency is more common in industrial settings or confined spaces (compressed CO2 releases, dry ice storage, fermentation rooms, tanks, cellars), not typical residential living areas.
Symptoms: Carbon Dioxide Poisoning vs Carbon Monoxide
CO poisoning symptoms (treat as urgent)
CO poisoning symptoms can look like a virus or food poisoning: headache, dizziness, weakness, nausea/vomiting, chest discomfort, and confusion. Severe exposure can cause loss of consciousness. A key clue is pattern: multiple people feel sick in the same space, symptoms improve when leaving, or a CO alarm activates.
High CO2 exposure symptoms
High concentrations of CO2 can cause headache, shortness of breath, faster breathing, dizziness, confusion, and in extreme cases collapse. These effects are usually associated with unusual high-CO2 environments (confined spaces or industrial releases), rather than everyday home ventilation issues. If you suspect a compressed-gas release or anyone has severe symptoms, leave the area and seek emergency help.
Signs of Carbon Dioxide in Your House
In most homes, "signs of carbon dioxide in your house" really means signs of poor ventilation: rooms feel stuffy, people feel sleepy, and odors linger. A CO2 monitor can help you decide when to ventilate, but it does not replace a CO alarm.
If you ever suspect a compressed CO2 source (e.g., a cylinder) leaking indoors, treat it seriously: ventilate and evacuate if symptoms occur.
Detectors: Do You Need a CO Alarm, a CO2 Monitor, or Both?
Do CO detectors detect CO2?
No. A standard CO alarm is designed to detect CO and alarm at specific thresholds over time. It does not measure CO2.
Do CO2 monitors detect CO?
No. CO2 monitors measure CO2 (often for indoor air quality/ventilation). They are not designed to warn you about CO poisoning.
Best-practice setup for most homes
- Install CO alarms on every level and near sleeping areas (follow local code and manufacturer instructions).
- Use a CO2 monitor only if you want a ventilation indicator — especially in bedrooms, nurseries, and home offices.
- Maintain combustion appliances and never run engines or generators in enclosed spaces.
What to Do If You Suspect CO
If your CO alarm sounds or you suspect carbon monoxide exposure, get everyone (including pets) to fresh air immediately and call emergency services from outside. Do not go back inside until responders confirm the building is safe, and have fuel-burning appliances inspected before using them again.
Full emergency checklist: What to do if you suspect a carbon monoxide leak.
Frequently Asked Questions
Is CO the same as CO2?
No. CO (carbon monoxide) and CO2 (carbon dioxide) are different gases with different risks. CO is a toxic poison gas from incomplete combustion; CO2 is a normal component of air that becomes dangerous mainly at very high concentrations.
Which is more dangerous: carbon monoxide or carbon dioxide?
In typical homes, CO is usually the bigger immediate danger because it can cause life-threatening poisoning at relatively low concentrations and is hard to detect without an alarm. CO2 is typically a ventilation/comfort signal at home, with acute danger mainly in unusual high-concentration releases.
Do CO detectors detect CO2?
No. Standard CO alarms are designed to detect carbon monoxide only. A CO2 monitor measures carbon dioxide for ventilation awareness.
Can high CO2 make you sleepy?
Many people associate higher indoor CO2 (often a sign of low ventilation) with sleepiness or reduced alertness. It is not the same as CO poisoning. Improving ventilation is the typical response.
What are CO2 leak symptoms?
At very high concentrations, CO2 exposure can cause headache, shortness of breath, dizziness, confusion, and in severe cases collapse. These situations are more typical of industrial/confined-space releases than everyday residential living areas.
Sources & References
- OSHA Chemical Database: Carbon Monoxide (CO)
- NIOSH IDLH: Carbon Monoxide (CO)
- NIOSH Pocket Guide: Carbon Dioxide (CO2)
- NIOSH IDLH: Carbon Dioxide (CO2)
Published: January 15, 2024