A small electric fan, mounted in the upper corner of a doorway, that moves
air from one room to another and thereby helps equalize temperatures in
both rooms; typically the motor in the fan is reversible. One of the problems
with a solid-fuel fireplace or stove is that although it may heat the room
it is in very well, it may leave other rooms cold. Doorway fans are a convenient
way of getting around this problem by circulating warm air to other parts
of the house. They are cheap to run and can pay for their purchase cost
withing a single heating system.
Disdvantages of doorway fans is that they do slightly obstruct, and may
detract from the appearance of, a doorway. The amount of noise they make
varies from one model to another.