A vent system for use with a patient interface during respiratory therapy of a patient with a therapy flow of gas pressurized above ambient pressure, the vent system providing a vent flow of gas to discharge gas exhaled by the patient from a pressurized volume, the vent flow of gas being continuous during the respiratory therapy, the vent system comprising a vent housing comprising a base having at least one first orifice extending through the base to allow gas to be discharged to atmosphere from the pressurized volume; at least one second orifice to allow gas to be discharged to atmosphere from the pressurized volume; a vent housing connector having a second orifice configured to direct the therapy flow of gas to the patient interface; a heat and moisture exchanger (HME) comprising an HME housing and an HME material within the HME housing; and a membrane positioned adjacent to the base, wherein the vent housing and the vent housing connector are configured to be connected to, at least in part, form a cavity, and wherein the HME is positioned in the cavity when the vent system is assembled, wherein the pressurized volume is in fluid communication with atmosphere through the at least one first orifice and the at least one second orifice throughout a therapeutic pressure range, and wherein the membrane is elastically deformable due to pressure within the pressurized volume to apportion the vent flow of gas between the at least one first orifice and the at least one second orifice throughout the therapeutic pressure range.
