CO can be produced by the combustion that occurs from fossil fuel burning appliances like a furnace, clothes dryer, range, oven, water heater, or space heater. When appliances and vents work properly, and there is enough fresh air in your home to allow complete combustion, the trace amounts of CO produced are typically not dangerous. And normally, CO is safely vented outside your home.

Problems may arise when something goes wrong. An appliance can malfunction, a furnace heat exchanger can crack, vents can clog, or debris may block a chimney or flue. Fireplaces, wood burning stoves, gas heaters, charcoal grills, or gas logs can produce unsafe levels of CO if they are unvented or not properly vented. Exhaust can seep into the home from vehicles left running in an attached garage. All these things can cause a CO problem in the home.