A gas deposition system (1000) configured as a dual-chamber “tower” includes a frame (1140) for supporting two reaction chamber assemblies (3000), one vertically above the other. Each chamber assembly (3000) includes an outer wall assembly surrounding a hollow chamber (3070) sized to receive a single generation 4.5 (GEN 4.5) glass plate substrate through a load port. The substrate is disposed horizontally inside the hollow chamber (3070) and the chamber assembly (3000) includes removable and cleanable triangular shaped input (3150) and output (3250) plenums disposed external to the hollow chamber (3070) and configured to produce substantially horizontally directed laminar gas flow over a top surface of the substrate. Each chamber includes a cleanable and removable chamber liner assembly (6000) disposed inside the hollow chamber (3070) to contain precursor gases therein thereby preventing contamination of chamber outer walls (3010, 3020, 3030, 3040).