A humidifier apparatus for operating at an air pressure is disclosed for use with a respiratory therapy breathing apparatus that provides a breathable gas supply to patients requiring higher concentrations of liquid vapor and gas pressure. The humidifier apparatus includes a feed liquid supply bag in fluid communication with a humidifier cartridge via a conduit. The conduit enables air to flow therethrough to equalize air pressure between the humidifier cartridge and the feed liquid supply bag in response to liquid being supplied to the humidifier cartridge.