Which factor is least likely to influence the efficiency of an air filter?

The cost of the filter is least likely to influence its efficiency because efficiency is primarily determined by how well the filter can remove contaminants from the air it processes, rather than the price of the filter itself. Efficiency is more closely related to the design, materials, and technology used in the construction of the filter, as well as the frequency of maintenance and the types of contaminants it is designed to capture.

In contrast, factors such as the frequency of maintenance directly impact how well a filter performs over time. Regular maintenance ensures that the filter remains clear and effective at trapping particles. The type of contaminants present is also crucial, as some filters are designed for specific types of contaminants and may not perform well against others. The condition of the bowl can affect airflow and the overall system efficiency, making it another important consideration. Therefore, while cost is important in terms of budget, it does not directly bear on the efficiency of the air filter in the same way as the other factors.