Voldam Mixed Flow In-Line Duct Fan Voldam Mixed Flow In-Line Duct Fan (Exhaust / Blower) may be used to solve many air moving problems. They are capable of moving airflow through long or complex duct runs, and provide an ideal solution for areas that are hard to heat or cool. Voldam Mixed Flow In-Line Fans are designed for residential and light commercial ventilation applications. These compact, powerful and quiet fans feature a durable and a two speed motor energy efficient.