Air washers are designed to help clean your air while providing healthy moisture to your space. This is a great benefit if you suffer from mild allergy or asthma symptoms. Often, air washer humidifiers use impeller technology, in which a series of spinning plates continuously filter out large allergens and particles from the incoming air. This prevents harmful impurities from being released into your breathing space. Alternatively, an air washer system may use a special air-washing pre-filter, similar to an air purifier pre-filter, to remove large particles before the air is humidified and dispersed.