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Installing a 4-5 in media air cleaner (filter cabinet) in the return at the furnace or air handler

A media air cleaner is a sheet-metal cabinet with a deep pleated cartridge that mounts in the return air path right before the blower. It must be on the return (never the supply), sit before any AC coil, have the face of the filter at right angles to the airflow, have its arrow pointing toward the furnace or air handler, and leave room in front to pull the cartridge. Seal every joint and use turning vanes when an elbow is tight against the cabinet. Changing return ductwork on a gas furnace can affect combustion air and venting; Trion's manual says to involve a heating contractor.

Cross-checked ~150 min advancedBrands: Trion, Trane, Honeywell, Aprilaire, All

Before you start

  • Turn off power to the furnace or air handler before cutting the cabinet or return
  • Gas furnaces: do not alter return ducting in a way that pulls air from the furnace room (combustion air) or blocks access to burners and vent; refer venting questions to a licensed tech
  • Wear gloves; cut sheet metal is sharp

Diagnostic steps

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Installing a 4-5 in media air cleaner (filter cabinet) in the return at the furnace or air handler · OnCall Tech