If indoor sources of CO exist, indoor levels will be higher than those outside. Avoid strenuous physical activity during peak traffic times, in high volume traffic areas, and during inversions . Heating season is a time of particular concern with regard to CO exposure. Gas and oil heaters that have not been used during the warm summer months should not be expected to perform efficiently without the benefit of service. It is imperative that furnaces be cleaned and serviced following the manufacturers instructions.
Winter is also the time of year when people use space heaters.
Flame color is a good way to check the combustion of a fuel-burning appliance. The flame should burn with a bright blue color. A yellow flame signals poor combustion and may indicate a problem with the flue or burner. Ideally, combustion air for fuel burning appliances should not be drawn from inside the home. Some newer furnaces draw air from outside the home and this alleviates the possibility of back drafting.