Many people these days suffer from respiratory problems, such as allergies, asthma, and emphysema. Even though air filters and air filtering devices have not been scientifically proven to remove allergens and decrease allergy and asthma symptoms, many people can testify to the benefits of air filters to increase their indoor air quality. Proponents of air filters note that it may take up to four months for your home to fully benefit from the air filter.

The reason it takes up to four months for maximum benefit is the air change rate. The Consumer Energy Center defines air change as: "The replacement of a quantity of air in a space within a given period of time, typically expressed as air changes per hour. If a building has one air change per hour, this is equivalent to all of the air in the building being replaced in a one-hour period." If the air change rate in your house is once an hour, then your filter will not be as efficient as if your air change rate was four times an hour.