In order to overcome problems that earlier apparatus and methods have experienced, an apparatus (10) for determining heat flux in an atmosphere of a freezer is proposed, said apparatus (10) comprising:- a housing (14) constructed to be transported by a conveyor (12) through the atmosphere- at least one heat source member (18) disposed at at least one surface (20) of the housing (14)- at least one heat flux sensor (22) operatively associated with the at least one heat source member (18) and- a self-contained power supply (26) mounted to the housing (14) for powering the at least one heat source member (18) and the at least one heat flux sensor (22).A related method of measuring heat flux in an atmosphere of a freezer is also proposed.
