Conventional air duct systems consist of a supply and a return. The supply ducts of an HVAC system supply heated or cooled air from the air handler to a main “trunk” line. The main trunk line carries the air to smaller “branch” lines, which then distribute the air to various locations throughout the home. The return side works in reverse. Stale air is pulled through return registers and into the branch lines. The air is then pulled through the main trunk line to the air handler where the air is filtered. it is then reheated or re-cooled and redistributed throughout the home
Typically most commercial duct cleaning projects are done by following the air flow of the system. Starting at the return registers and cleaning toward the air handler eliminate recontamination if the system is turned back on prior to completion. Once the returns are complete, the air handler is cleaned, then working outward on the supplies until the project is finished.