How to Convert High-Velocity Duct Systems to Low

High speed air duct velocity can create unwanted noise, especially if the ducts are the wrong size for the amount of airflow. Typically, the sources for excessive duct airflow is the fan. The wrong size fan operating at the wrong speed will create high or low frequency noise, necessitating replacement of the fan and motor to find the happy medium between airflow and ambient noise.

Things You'll Need

  • Wire snips
  • Adjustable wrench
  • Compressed air
  • Silicone spray
  • Clean cloths
  • Screwdrivers -- Philips, standard and Torx
  • HVAC fan replacement kit
  • Wire strippers
  • Red wire nuts


    • 1

      Shut off the main breakers at the panel powering the blower motor. Typically, these are labeled "furnace," "HVAC" or "air."

    • 2

      Twist the plastic knobs on the front of your air handler, located on the intake side of your furnace. Pull the metal door off the air return.

    • 3

      Locate the cylindrical fan motor housing. This fan operates whether or not heat, air conditioning or simple air recirculation modes are on.

    • 4

      Snip only the wires leading directly to the blower motor. Ensure you snip close to the motor, to leave enough wire to reconnect the new fan.

    • 5

      Loosen the two nuts holding the fan housing to the inside of the air handler. Place one hand under the blower motor housing as you remove the second nut, to prevent it from falling to the floor.

    • 6

      Unscrew the nut holding the existing fan in the motor housing. Flip the housing over, allowing the old motor to come out. Remove the brackets from the side of the old fan, if the new one is not supplied with any.

    • 7

      Blow out the housing with compressed air, silicone spray and a clean cloth to remove dust and accumulated contaminants.

    • 8

      Inspect the existing fan's specification label, located on the side. Replace the fan with one that uses the same electrical requirements, but has reduced PPM and speed. This is key to reducing duct noise.

    • 9

      Reverse the process, placing the new fan into the existing housing. Route the wires from the fan through the hole in the side of the housing.

    • 10

      Bolt the fan housing into the air handler. Strip one-half inch of insulation from the wires in the handler and the new motor.

    • 11

      Place like wire colors parallel together. Twist a red wire nut over each pairing. Replace any removed filters and the main door cover.

    • 12

      Turn the breakers powering the fan and air handler back on. Test the new fan, listening for reduced duct noise.

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  • Photo Credit Comstock/Comstock/Getty Images

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