• You use filters in your refrigerator, dryer and air conditioner units.Michael Blann/Photodisc/Getty Images
  
  Appliances use filters to remove unwanted particles from different substances. Sometimes filters remove annoying particles that may cause irritation but do not pose significant health hazards. Other filters help remove allergens from the air to lessen the impact they have on the people who live in the house. Still other filters remove dangerous particles that can have long-term health effects if they are not captured.
  
  

Refrigerators

• Modern refrigerators typically have a dispenser for water, or water and ice. The water that the refrigerator uses comes from the line that provides water for the rest of the house. Instead of using this ordinary tap water, refrigerators run the water through a filter first to clean it and remove annoying smells or particles.
  
  

Plumbing Systems

• Plumbing systems that draw their water from treatment plants do not need advanced filters to remove contaminants, but those that work with well water must have some type of filter system in place. Even clean water can be hard, or filled with dissolved minerals that can create scale and staining problems. A water softener can help treat these problems, and carbon filters can remove unwanted smells or chemicals.
  
  

Dryers

• Owners are well-acquainted with dryer filters, since they need more maintenance than most appliance filters. Dryer filters help catch the lint that is drawn off from clothes during the cleaning process. Without the filter, this lint would circulate with the clothes and stay attached to them, making it difficult to fully remove the lint and clean clothes properly. Dryer filters typically fill with lint after every large load of laundry and should be cleaned often.
  
  

Air Conditioners

• Nearly any device that circulates air also has some type of filter. Vacuum cleaners use filters to remove dust particles. Air purifiers use filters to take care of even finer particles conventional methods cannot remove. Air conditioners, however, are present in most modern buildings and use the largest filters. Some use UV devices that kill spores and bacteria in the air, but most use fiber filters to trap dust.