Why Vents Smell When the AC Starts
Odours can have several sources
Stale odours may come from dust in accessible ducts, old filters, moisture, pets, carpets or the furnace and coil area. The source matters before promising a fix.
When duct cleaning may help
If the odour follows visible dust, pet hair, renovation debris or a home with unknown history, duct cleaning can be a sensible first step.
Details to include
Mention whether the smell appears with heat, AC, fan-only mode, one room or the whole home. That helps the team ask better follow-up questions.