Between 1695 and 1850 a tax was levied on windows which encouraged people to have as few windows as they could, making it more important to get as much light through them as possible. The typical Georgian window is known as the double hung sash with six panes. This is a window with two frames (sashes) with six panes of glass in each, they were then hung one above the other inside the window opening. The Sashes are then opened by either raising or lowering them past each other. A system of ropes and counterbalancing weights ensure the windows remain open or closed.
Sash windows are seen as one of the most efficient types of window in terms of allowing fresh air to enter a space. If both the top and bottom sash are both opened slightly warm air can escape from the top and cooler, fresh air can enter at the bottom