How to Set the Gas Furnace Blower and the Temperature Limits

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A furnace blower or a fan (the terms are really interchangeable) regulates when a heating system in a home or business sends its warmth out into the ducts and vents of a building. Both the blower and the temperature limits can be controlled and reset using a device within the furnace called the temperature limit control. According to furnace expert Paul E. King, "Even the most inexperienced homeowner should be able to locate and reset the temperature controls for the furnace." More extensive work may require a trained professional.

Things You'll Need

  • Screwdriver
  • Flashlight
  • Turn off the power supply to your furnace at your main electrical panel.

  • Open up the access panel of your furnace. Remove the sliding door or use a screwdriver to unscrew it.

  • Shine a flashlight into the furnace for help finding the limit control. You'll be looking for a small box with a button sticking out of it. Generally it's located in the upper portion behind the access panel.

  • Slide the front of the temperature limit up or off varying by product. Shine your flashlight onto the inner section of the limit control to see a dial with increments marked off.

  • Move the metal hand farthest to the left to set the blower "off" position. This hand tells the blower to shut off if the furnace has cooled down. Most furnaces come set around 100 degrees Fahrenheit for this temperature control.

  • Set the second hand from the left to about 140 degrees. This control tells the fan when to come on and distribute the heat once the furnace has warmed up enough.

  • Check the third hand farthest to the left and ensure it is set at around 210 degrees. This is just a safety precaution to tell the furnace to shut off if it gets too hot. Most furnaces have a built-in shutoff control, so this is usually just a precaution.

  • Pull out the white button at the bottom of the temperature controls. This will tell the blower to run on automatic and follow the temperature settings you've made.

  • Replace the access panel and restore the power to your furnace.

Tips & Warnings

  • Changing any other part of the furnace besides the temperature limit controls may result in personal injury or damage to the heating system.


  • "The Furnace Book: The Heart of Your Home"; Paul E. King; 2004


  • Photo Credit Home sweet home image by Jigsaw from

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