How do I Fix a Blocked Heating Duct?


When approaching the winter months, it may be time to turn on your furnace to check the heat output of the heating ducts. If you do not feel heat coming from the vents in your home, there may be a clog in one of the heat ducts. When your heating system sits idle over the summer, clogs can appear from dust and loose dirt that accumulate in the ducts. Removing the clogging debris is necessary for your heating system to work properly and produce an adequate amount of heat.

Things You'll Need

  • Screwdriver
  • Flashlight
  • Wet-dry vacuum
  • Tape
  • Plastic bag
  • Goggles
  • Mask
  • Gloves
  • Turn off the furnace by switching the button on the thermostat to the off position.

  • Remove the vent grate. This is also a good time to remove any dust and loose dirt that may be on the vent grate. You may need a screwdriver if the vent has screws holding it in place.

  • Shine the flashlight into the duct and look for debris that may be causing the clog.

  • Remove the clogging debris. If you can not remove the debris by hand, use the vacuum with a brush attachment. For debris that may be lodged in the duct, place the brush head as close to the debris as possible. This will create a seal and increase the suction.

  • Vacuum the vent opening and duct to remove any loose dirt or debris that may cause a duct clog in the future.

  • Check the airflow of the duct. Tape the opening of a plastic bag to the vent opening. Turn the furnace on. If the bag begins to move rapidly then the clog has been removed.

  • Return the vent grate to the vent opening. Secure any screws with the screwdriver if necessary.

Tips & Warnings

  • Always wear goggles, gloves and a mask to prevent any debris from getting into your eyes and/or lungs.
  • If any type of mold or insect is in the duct, replace the vent grate and contact a professional immediately.
  • If the plastic bag does not appear to be moving after you have turned the furnace on, the clog is probably in a location you can not see or reach and a professional may be needed.

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  • Photo Credit security and heating system image by Canakris from
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