Use renovation evidence to define the cleaning area
Sanding and drywall work can leave fine material near registers or inside ductwork, especially if the system operated while dust was present. The amount and distribution should be inspected before deciding whether a cleaning is warranted. Affected branches, registers, and accessible equipment connections help define the work; a general claim that every duct is contaminated is not evidence. Protecting finished surfaces during any cleaning process is also part of planning the scope.
