Abstract: A bypass air filter is provided for attachment to the return air duct of an existing forced air conditioning system. The bypass air filter has a housing that defines a bypass air channel between an air inlet opening and an air outlet opening. The housing attaches directly to the return air duct so that the air inlet and outlet openings connect with complementary openings in the return air duct. This arrangement eliminates the need for bypass air ducting between the return air duct and the bypass air filter. The housing retains an air filter, which bisects the bypass air channel, and a fan for drawing air in through the air inlet opening through the air filter and out the air outlet opening. An upstream baffle extends from the housing into the upstream air flow through the return air duct to direct air into the air inlet opening. A downstream baffle extends from the housing away from the upstream air flow through the return air duct to draw air out of the air outlet opening.

Abstract: A bypass air filter is provided for attachment to the return air duct of an existing forced air conditioning system. The bypass air filter has a housing that defines a bypass air channel between an air inlet opening and an air outlet opening. The housing attaches directly to the return air duct so that the air inlet and outlet openings connect with complementary openings in the return air duct. This arrangement eliminates the need for bypass air ducting between the return air duct and the bypass air filter. The housing retains an air filter, which bisects the bypass air channel, and a fan for drawing air in through the air inlet opening through the air filter and out the air outlet opening. An upstream baffle extends from the housing into the upstream air flow through the return air duct to direct air into the air inlet opening. A downstream baffle extends from the housing away from the upstream air flow through the return air duct to draw air out of the air outlet opening.

Abstract: An in-line centrifugal fan including a housing having an inlet and an outlet spaced apart and substantially coaxial one to another and a motorized centrifugal-type impeller mounted centrally within the housing substantially coaxially between the inlet and the outlet. A plurality of spaced air flow redirecting vanes are each connected to and radially extend inwardly from the housing toward, but not to, a radially outermost perimeter of the impeller whereby air flow through the housing is increased by the vanes. Various vane configurations, clearances and number of vanes are disclosed.