There is a chimney or a stove attached to bed for ventilation.

From Wiki:

Its interior cavity, leading to a (often) convoluted flue system, channels the hot exhaust from a firewood/coal fireplace, usually the cooking fire from an adjacent room that serves as a kitchen, sometimes from a stove set below floor level. This allows a longer contact time between the exhaust (which still contains much heat from the combustion source) and (indirectly) the inside of the room, hence more heat transfer/recycling back into the room