Convection door

Interior doors divided horizontally that extend to the ceiling are called convection doors (also lev doors). They have two leaves: a standard-height lower leaf and a smaller, matched-designed upper leaf.^[1][2]

Convection doors eliminate the need for ducting by facilitating efficient convection of warm air from central heat sources, such as air conditioners and fires, through buildings in cold climates. In warmer climates, the doors let cool cross-breezes pass through freely when the main door leaf is closed. Air circulation and privacy can be controlled independently with this design.

The doors were first used in works of Australian architect Jiri Lev.

In structures, warm air rises from the heat source and progressively spreads across the ceiling. As it cools and reaches the walls, it begins to drop and return to the heat source, filling the void left by additional warm air rising. Conventional door apertures are limited in the amount of warm air that can enter adjacent rooms since they only extend 400-1200 mm below ceilings, posing as a barrier to warm air that moves along the ceiling. Convection doors, like other floor-to-ceiling doors, span the entire height of the room, allowing warm air to circulate freely.

Temperature readings show that secondary rooms are typically about 2 °C colder than primary rooms (which are the rooms with the heat source). Convection doors allow auxiliary rooms to have temperatures that are usually the same as primary rooms.