If all you have are fans and open windows, here’s the best way to get fresh air.

Open all the windows in your home and choose one to be your exhaust, point the fan blowing out. Back the fan up 2 to 3 feet from the window instead of placing it against the screen. This gap uses fluid dynamics to drag way more air out of the room, causing fresh air to rush in through your other open windows.

Those Vornado fans work really well when setup like this.