Apparatus and methods for delivering a heated and humidified mixture of oxygen and air are provided. The apparatus includes an air compressor and oxygen concentrator enclosed in the housing of a vapor transfer system. The air compressor supplies air at a first pressure to a gas inlet. The oxygen concentrator provides oxygen at a second pressure to the gas inlet. The oxygen concentrator and the air compressor are in fluid communication and are configured such that the first pressure of the compressed air and the second pressure of the oxygen are about equal. The apparatus includes a vapor transfer system having a gas passage, a liquid passage having heated liquid and vapor, and a membrane that separates the gas passage and liquid passage. The membrane is positioned to transfer vapor from the liquid passage to the gas passage.