Many people confuse hopper windows with awning windows because both are hinged, open into or out from a room. An awning style casement window is hinged on the top and opens out from bottom up, creating an awning like appearance when it is open. The full screen is mounted on the inside. A hopper window, on the other hand, is hinged on the bottom and tilts open at the top so the entire window can be opened. It has a crank handle and a mechanism that holds the window in place, preventing it from slamming shut in the wind. The window screen attaches on the outside. When either a hopper or awning window is positioned over a door, it is called a transom window.
Hopper windows are typically used in areas that require small openings, like basements and bathrooms, that also need as much ventilation as possible, for which a hopper window is ideally suited since, unlike windows that slide, it opens completely and requires a limited amount of space. The hopper window accommodates a full window screen because the window opens inward, away from the screen. A hopper window is more effective at preventing air leakage than other standard window types because the sash presses against the frame when it is closed. These windows seal more tightly than is possible for the sliding seals in traditional windows, keeping heat or air conditioning in and the elements, out.