Question: Hot combustion gases from a large burner are being considered to heat cold water in a heat exchanger. To facilitate operation and maintenance of the two units, they have been separated and installed individually. The client failed to provide specific information regarding the heat exchanger and conduct verification of the presence of electronics and electrical boards on the unit. As per the 2006 NFPA Standard 31, Section 4.3.6, oil-burning equipment must be installed so that a minimum 3 ft separation is maintained from any electrical panel-board. The design strategy will be to connect a duct to the burner and route it to the bottom of the heat exchanger. It is expected that 25000 lb/h of corrosive combustion gases at 600?F will be transported through the duct after combustion with a low air/fuel ratio. The duct will be routed through the concrete slab of the floor in a trench to provide insulation, support, and protection. Design and layout a low-velocity rectangular duct system. Further Information: For the system designed, the maximum length of straight duct will depend on the fact that the burner blower cannot provide more than 0.35 in. wg of pressure.