Updated: Jul 8, 2022
Carbon monoxide – called the silent killer, you can’t smell it, see it or taste it, but when you breathe it in, your blood cells attach to it rather than attaching to regular oxygen molecules. It comes from any appliance in your house that burns fuel, like water heaters, driers, and gas ovens. It can also come from a running car.
Mild exposure will give you symptoms like headache, nausea, fatigue, etc. High levels of exposure can lead to a coma and/or death.
Manufacturers of carbon monoxide detectors explain exposure levels from low to dangerous:
Low: less than 50 PPM
Medium: Between 51 - 100 PPM
High: Above 100 PPM
Dangerous level: Anything above 100 PPM
Carbon Monoxide Alarm Settings
Carbon Monoxide Level
Alarm Response Time
1 to 4 hours
10 to 50 minutes
4 to 15 minutes
The EPA and ASHREA, American Society of Heating, Refrigerating and Air-Conditioning Engineers, recommend indoor levels be kept below an average of 9ppm over 8 hours. Ovens can put out 30 ppm on startup but should not go over 30ppm.
Inspections Over Coffee home inspectors all carry portable carbon monoxide detectors and take measurements near all indoor fuel-burning appliances.