Supply/extract air volumes and input powers Figure 1. Supply and extract air volumes Supply and extract air volumes - description of the diagram Continuous line (—) Extract air Broken line (- -) Supply air SFP = Input power (total) (W) Air flow specified in the ventilation plan (extract l/s) The recommended SFP rate (Specific Fan Power) value <2.0 kW/m3/s). When a lower total pressure is used, also the SFP of the speed is lowered. Figure 2. Fan input power