Any HVAC experts in the house? Does anyone know of any engineering standards concerning the placement of flow straighteners downstream of a fan in a duct? I'd hate to just choose an arbitrary distance without any justification other than "well, it just seemed like it was good enough." So are there any relations such as "the flow straightener must be placed X duct diameters downstream from the fan outlet" or something to that effect? I know the straightener just reduces swirl and helps produced a more uniform flow, so maybe its distance from the fan outlet isn't significant as long as it's somewhat close? Then again I want some scientific reasoning to justify it, not just conjecture.