During the Standard Air Duct Cleaning process, the technician attaches an industrial vacuum hose (about 6 inches in diameter) to the ductwork near your furnace, creating negative air pressure throughout the duct system. To do this, he creates an access point (a hole), using a drill and tin snips, that will later be covered with a piece of galvanized sheet metal (otherwise known as a cover plate). If you already have an appropriately positioned access point, he will use the existing one.
Once the access has been created and the vacuum is in place, the technician then services each supply and return vent with an air wand. This device has a nozzle approximately one foot long. It is pliable and fits in between the fins of the registers, exerting roughly 200 lbs. of air pressure. The technician is able to angle the air wand to force any dust and debris down the branch lines and into the main trunk lines.
After all the registers and branch lines have been serviced, the technician moves to the main trunk lines, near your furnace. At this point, an air snake, with a reverse air nozzle, is utilized. In order to create access to these lines, one or more 1-inch holes (which will later be plugged with rubber duct plugs) are drilled into the main trunk line. The technician then inserts the air snake into each hole, one at a time, and, with the help of the reverse air nozzle, the air snake propels itself forward to the end of the trunk line. Then with the air pressure still engaged, the air snake is slowly pulled back toward the furnace, during which time it jostles around inside the trunk line, dislodging dust and debris and bringing it back toward the furnace, where our vacuum catches it. No mess involved!
It is generally recommended that the furnace filter be replaced after air duct cleaning, but if a new filter is not immediately available, the technician can clean your existing one with air pressure (outside your home, of course!) until a new one can be obtained, typically within a week. This will also give the furnace time to cycle through any residual dust that may remain in the system.
Once the technician is finished with the air duct cleaning process, he turns the furnace on to ensure everything is operating smoothly. Sometimes a slight burning smell can be observed when the furnace is first turned on as any residual dust is burned off.