In a home with central or ducted air conditioning, every breath of cooled air travels through ducts hidden above the ceiling. Over the years they collect dust, and in humid conditions mould. Duct cleaning is not something you need every few months — but when it is due, the difference is noticeable.
Look at the vents
Dark dust marks around the grilles, or dust blowing out when the AC starts, are the clearest signs. Remove a grille and look inside with a torch.
Notice the dust in the house
If surfaces are dusty again a day or two after cleaning, the AC may be circulating it from the ducts.
Pay attention to smells
A musty smell that appears when the AC runs and fades when it is off suggests mould somewhere in the system.
Think about allergies
Sneezing, itchy eyes or a blocked nose that are worse at home than outdoors can be linked to what is in the ducts.
After building work
Renovation creates fine dust that is drawn into the return air and settles in the ductwork. Clean the ducts once the work is finished.
Know what a proper job includes
The grilles and diffusers are removed and washed, the ducts are brushed and vacuumed along their length, and the fan coil unit, coil and drain tray are cleaned as well. Vacuuming only the vents does very little.
How often
Every two to three years suits most homes. Earlier if you have just moved in, had building work done or noticed any of the signs above.
