In homes, the main sources of carbon monoxide (CO) are heating and hot water systems (boilers) and cooking appliances (stoves, barbecues, and fire pits). A vehicle engine in an unventilated garage, or generators placed in a garage or basement, can also produce CO.

These sources of CO found in residential settings are also present in public venues (such as theaters, ice rink restaurants, community centers, or places of worship). Other sources are specific to these types of venues, such as certain combustion-based heating devices (gas radiant heaters, ice resurfacing machines in ice rinks).

In the workplace, the main sources of carbon monoxide are internal combustion engines, gas-powered machinery (forklifts), furnaces, as well as heating and hot water systems, generators, etc.