When to use whole house fan
I'm located in Miami and installed a whole house fan two years ago and love it. The best time for it is in the winter and yes, you have to open windows and/or doors. The fans are powerful, probably 5400 +- cfm. If the air is moving out, it's got to come in from somewhere. Winter is great because you get that cooler air flowing through the house, summertime, not so much. You would be able to draw some cooler air from downstairs to the top floors during the summer but be careful you don't draw up too much and cause your AC to over work. For the most part, I don't use the whole house fan during the summer unless the temp drops after a rainstorm. Then I open the windows, turn on the fan and air out the place.
Pollen hasn't been a problem but that would depend on the individual.