Many homes in Canada are heated and cooled with forced air systems of various types. If your home is heated with a furnace or cooled with a central air conditioner, then you likely may have an extensive duct system running throughout your house even if you don’t see most of it. What Is Duct Cleaning? This duct system is used to move air around your house thus it is responsible for delivering the heated or cooled air to the supply vents ( this controls the indoor temperature ), returning air from the rest of the house back to the furnace or air conditioner and venting air to the outside. Over time these ducts become dirty because of a number of contaminants such as: Mold, dust, pollen, allergens, obstructions ( toys, construction debris), rodents and their feces and pet dander. more... See more text