Abstract: Fan assemblies, mechanical draft systems and methods are provided. In this regard, a representative mechanical draft system for use with multiple appliances includes: a chimney operative to direct combustion products from multiple appliances; a chimney fan operative to draw combustion products from the chimney; and a controller operative to adjust an operating speed of the chimney fan such that, responsive to a change in pressure in the chimney, the controller adjusts the operating speed of the chimney fan to maintain a desired pressure in the chimney.