Windows are typically replaced when they become difficult to operate or lock, when a draft can be felt when closed, or when there is moisture present between the panes of glass (called a seal failure). Sometimes they just look old and worn over time. New windows are going to be more energy efficient, look better and typically block more outside noise. There is also oftentimes better fade protection where sun enters the windows hitting furniture, flooring, etc. Energy efficient replacement windows come in an array of styles, sizes, shapes and colours.