This is the standard industry base package - 10 air vents. Additional air vents are a way of telling us the size of the system and the additional work it might require, therefore there is an additional charge of $9.95 per additional vent. It includes the average minimum amount of vents in a service job and it acts as a base rate for any duct cleaning job. Since all houses are different in size, shape, and systems there is no 'one package' fits all, but rather a base package to which additional charges are added according to the custom need of the house or building.