Enjoying big machines, I went a little overboard on our new ventilation system:
Nights here are usually 20+ degrees cooler than day time. This meter-wide array consists of twin 20" fans, pushes nearly 9K CFM. On high, it will thoroughly pre cool our entire place (both floors) in a couple of hours.
Playing around with different configurations, we've made a discovery. Nearly all allergens in our area are confined to the 1st floor. Set to pull in air from the 2nd floor, positive pressure evacuates pollen and other allergens and keeps them out. No filters, no medications. We can leave them running on low or Just seal up the windows before turning them off.
Performance will vary with location, but another option for allergy suffers to consider.