A great way to improve the quality of your HVAC system yourself is to replace your furnace filters on at least a monthly basis. This is true during the cooling season as well. The cool air from your central air conditioner flows through the same ductwork as does your heated air. So whether it is winter or summer you should change your furnace filter on a monthly basis. Always remember, that when changing your filter(s), it is extremely important to purchase the proper size. If the wrong size filter is placed into your system, it will allow air to leave the system, making your air purifying system useless. Call Nortek Environmental, Inc. at (630) 548-1500 for all of your heating, cooling and indoor air quality needs.