Abstract: A combustor assembly of a water heater, which is provided between an air blower and a burner set to guide air from the air blower to the burner set, includes a first board, a second board and a third board stacked in sequence. Between the first board and the second board there is a first chamber and a first port, and between the second board and the first board there is a second chamber and a second port. The second board and the third board both have apertures. These boards restrict and divide an air flow of the air blower to flow along several paths to increase heat efficiency.