AO Smith Vertex and ProMax residential gas water heaters represent innovative technology designed to maximize efficiency and quality. The Vertex power-vent and power direct-vent gas water heaters take high-demand homes to the pinnacle of hot water availability. Vertex offers up to 96% thermal efficiency with performance that rivals much larger water heaters. ProMax water heaters are engineered to help lower your energy bills and provide exceptional reliability. They go the extra mile in safety innovation with C3 Technology that protects against accidental ignition of flammable vapors.