A breathing tube for a patient ventilator system providing humidified breathable gas is provided, the tube including inhalation and exhalation pathways formed in part by inhalation and exhalation tubes. A coupler member is attached at one end to the exhalation tube and forms part of the exhalation pathway, the coupler member has an integrated coupler-member electrical heating device electrically connected to the tube-portion electrical heating device. A connecting piece is detachably attachable to the other end of the coupler member and forms a part of the exhalation pathway, the connecting piece and coupler member together forming a hollow space therewithin extending from within the connecting piece to within the coupler member. A filter element is within the hollow space and extends from within the connecting piece into the coupler member, the coupler-member heating device is along the hollow space, surrounding the filter element, and adapted to heat the filter element.