Double Hung Windows 

Double Hung Windows differ from their single-sash counterparts by offering ventilation through both the top and bottom sash—even at the same time. When both sashes are open, cool air will circulate through the bottom sash and warm air will circulate out through the top. A standard double hung window will come with a half screen and is considered a typical replacement style. Both sashes will tilt into the room to allow for easy surface cleaning.