You can visually inspect the HVAC system on your own, and that will give you some clues since the reason most facilities call in a duct cleaning company is because of visible dust and debris buildup in the ducts.
But it’s imperative that the ducts are fully cleaned especially since that’s what your facility is paying for, and also because any leftover dirt accumulation shrinks the HVAC passageway, potentially lowering efficiency and raising your energy bills.
The first thing you should do is request a thorough visual inspection from the duct cleaning provider. Some duct cleaning companies have remote photography systems to show their customers what the inside of the ducts look like. When viewing the photography every part of the ducts should appear clean. If you can see any dirt or debris, the ducts are not sufficiently clean.
In addition to a general visual inspection, it’s crucial to focus on the care and cleaning of key areas. Fortunately, the EPA provides a handy checklist. You may even want to give the duct cleaning company the list before its employees begin work to make your expectations clear. After the cleaning is done, you can walk through the checklist with the provider.
Has the service provider adequately demonstrated that duct work and plenums are clean?
Are newly installed access doors in sheet metal ducts attached with more than just duct tape (e.g., screws, rivets, mastic, etc.)?
Have all registers, grilles and diffusers been firmly reattached to the walls, floors and/or ceilings?
Do filters fit properly and are they the proper efficiency as recommended by HVAC system manufacturer?
Does the system function properly in both the heating and cooling modes after cleaning?