Hello,   My understanding is that the figure you're seeing is per PSU, so as you indicated, you would double the figure for a dual power supply configuration. 
I'm trying to calculate maximum heat dissipation for two server racks. The first is a PowerEdge R740 with a 495 W Dual, Hot-plug, Redundant Power Supply. The owners manual lists a 495 W AC PSU with a heat dissipation of 1908 BTU/hr, however it does not specify a heat dissipation for a redundant power supply. Should the total  heat dissipation be 1908 * 2 = 3816 Btu/hr to supply a redundant power supply?  The second is an NX440 with a 350W, dual hot-plug redundant power supply. The owners manual lists this as 1340 BTU/hr but it mentions that "the following specifications are for each PSU." Does this mean the total heat dissipation should be 1340 * 2 = 2680 Btu/hr? Any help would be greatly appreciated.
Heat Dissipation for PowerEdge R740 with 495W Dual, Hot-plug, Redundant Power 
Supply and NX440 Redundant Power Supply