An apparatus for enclosing a medium and/or high voltage unit connectable to an electric power system. The unit includes one or a plurality of electrical components and generates heat as a by-product during operation. The apparatus includes a housing including a main chamber housing a seat for holding the unit. The main chamber is arranged to house the unit. The housing includes at least one gas exit opening at an upper part of the housing and at least one gas entry opening. The housing includes a sound-absorptive gas exit chamber provided with the at least one gas exit opening. The housing includes a sound-absorptive gas entry chamber provided with the at least one gas entry opening. A first heat convection path is provided inside the housing between the at least one gas entry opening and the at least one gas exit opening, via the gas entry chamber, via the main chamber and via the gas exit chamber, in order to provide cooling. Each of the gas exit chamber and the gas entry chamber houses at least one sound-absorbing member for absorbing sound produced by the unit during operation. At least one of the gas exit chamber and the gas entry chamber has at least one heat conducting wall and at least one free space provided between the at least one sound-absorbing member and said wall such that the first heat convection path is provided inside the housing between the at least one gas entry opening and the at least one gas exit opening via the at least one free space.