Decide whether cleaning is warranted
EPA recommends considering duct cleaning based on conditions rather than a routine calendar for every home. Concerns worth investigating include substantial visible mold, pests or excessive debris in the system. Ordinary dust on a register does not establish that the entire duct system needs cleaning. [1]
Tell us about recent construction, filter problems, visible debris, odors and any history of water around the equipment. Ask to see the condition that supports the recommendation. Duct cleaning is not a proven way to prevent health problems, and no cleaning service can guarantee relief from a person's symptoms. [1]
Know which components are included
A register cover is the visible fitting over an air opening in a room. Behind it may be a metal boot, an insulated box or another connection to the duct system. The return side, air handler and supply runs are additional components. Cleaning the covers alone should be described as cover cleaning, so it is not confused with a broader duct or HVAC service.
The written scope should identify the components to be accessed, the cleaning approach, the protection around work areas and any exclusions. High ceilings, fragile covers and restricted equipment closets can change the access required. Discuss those conditions before the appointment and clear the immediate work areas as agreed.
Choose methods that suit the material
Metal, flexible duct and internally insulated ductwork do not all tolerate the same treatment. The cleaning plan should identify the material and its condition before selecting tools or products. Existing tears, loose connections or deterioration should be discussed rather than hidden by a general description of cleaning.
Ask how loosened debris will be collected, how nearby furnishings will be protected and how accessible components will be checked afterward. If a chemical product is proposed, request its name, purpose and suitability for that particular surface. A broad promise to sanitize everything is not a useful description of the work.
Recognize when remediation or replacement is needed
Cleaning is intended to remove deposits from components that can be serviced appropriately. Suspected mold requires attention to the moisture condition and affected materials. EPA advises replacing wet or moldy duct insulation because it cannot be effectively cleaned. A coating should not be offered as a substitute for resolving that condition. [1]
Where duct repair, replacement or mechanical work is needed, the proposal should identify that work and the appropriate HVAC professional. The cleaning scope and any separate remediation or repair scope should be clear before work begins.
Keep useful records after the work
Ask for a record of the components serviced, accessible conditions observed and any areas that still need attention. Photographs can help explain a finding when they identify the actual location.
Filter fit, the equipment manufacturer's maintenance guidance, drainage and the condition of accessible connections also deserve attention. A cleaning appointment is a useful opportunity to identify unanswered questions, but it does not replace the mechanical evaluation needed for an equipment fault or persistent condensation.
Sources & further reading
These sources support the general guidance. The work at a particular property depends on its conditions and agreed scope.