Abstract: A bed ventilator includes an electric motor driven axial flow fan for moving air between a mattress and a bed cover thereon. The fan and associated duct work is mounted on a thin flat support tongue extended beneath the mattress and sandwiched between the mattress and its supporting bed structure such as a box spring. The associated duct work includes telescopic duct sections adjustable to accommodate mattresses of different thickness and locking screws are provided for securing a selected telescopic relation between the duct sections for a particular mattress involved.