Density of truss work create a problem?

At what point does the density of truss work become a problem for the fans? Do you really need the 4' downtube if the truss structure is open above? The area above the fan is essentially the inlet and requires enough space to allow large volumes of air to pass through. As a rule of thumb, we like to see a minimum 20-25 percent of the diameter of distance above the fan. Our standard downrod lengths are based on the expectation that the majority of installs have open truss area above the mounting point. Not all applications are the same. To evaluate what is best for your application, we recommend talking to one of our experts.