Your vacuum's agitator brush and exhaust whip up dust that eventually settles on the surfaces you've just cleaned. Filter out some of that dust before it settles by switching your thermostat to 'fan on.' This turns on the blower inside your furnace and filters the air even while the system isn't heating or cooling. Leave the blower on for about 15 minutes after you're done cleaning forhow to remove dust from air. But don't forget to switch it back to 'auto.' Most blowers aren't designed to run constantly. Plus: Here are 8 simple furnace fixes you can do yourself.