Abstract: Venting difficulties in a heat battery including a first container (10) for housing a heat storage salt that may be in the solid phase or in the liquid phase, a heat exchanger (22) within the container (10) and a second container (12) surrounding the first container (10) in generally spaced relation to provide an insulating space (14) about the first container (10) along with coolant inlet and outlet connections (40, 42) to the heat exchanger (22) are avoided in a vent system (52) including a vent inlet (66) generally centrally located in the top wall (56) of the first container (10) generally centrally of the ends thereof. A vent passage includes a check valve (106) located in close proximity to the vent opening (66) and the vent opening is surrounded by a cup shaped baffle (60) having an opening (62) facing the interior of the container (10). A filter (78) is located between the check valve (106) and the opening (62) to the baffle (60).