Guarding Other Entry Opportunities
Animals carry with them innumerable amounts of dust, pollen, allergens and bacteria. Once they enter your house and the air ducts, those particles and pathogens spread into your air supply. Keeping them out of the house in the first place becomes a priority.
Apart from windows and doors, search for other entryways by which animals may enter. Take special notice of places less frequented by family such as storage units like the attic and garage. Any cracks, crevices and holes are possible entry points.
Try to have these sealed to prevent animals from wedging their way through. This also assists in regulating the amount of outdoor air entering, so that the air quality and temperature inside stay as consistent as possible.