This is my second purchase of this fan, I got the second one to supplement the first during warmer weather and to have as a backup since my original unit was purchased several years ago.  I use these to pull cool night air through the house.  They are set up in windows in one room, and at night I open other windows in the house a few inches each.  Used on exhaust, this fan can pull a lot of air though the house overnight, in fact it is usually downright chilly before dawn!  I'm home most days, so if it's going to be warmer than mid seventies during the day, I let the house cool off as much as it can overnight and just dress warmly in the morning, then change into something cooler as the house warms up later in the day.  The $$ I've saved in electric bills more than makes up for the trouble of changing clothes or taking off a fleece cardigan.