Storm windows are windows which are mounted outside or inside of the main glass windows of a house.[1] It may also refer to a small openable flap found in the side window on light aircraft.
Most commonly, they are found in cold climates to serve as a retrofit on existing windows in order to improve their thermal efficiencies.[2] Similarly, storm doors (also called "screen doors") allow similar energy savings with less efficient primary doors - and allow a screen for summer ventilation.
Storm windows can be mounted externally or internally; can be made of glass, rigid plastic panels, or flexible plastic sheets; and may be permanently or temporarily mounted. They function similarly to insulated glazing.