i am not a very heavy pc user, when the pc is off, many dust come into my pc from the top blowhole. I wanted to use a duct but it will look weird on top of my pc, placing a filter will surely cut down my exhaust fan airflow. Pls don't sugggest me to cover the blowhole when not in use, i am a forgetful guy, sometime i leave my pc off automatically so i can't even do it.