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    sharonbb's Avatar
    sharonbb Posts: 3, Reputation: 1
    New Member
    		  
    #1

    Sep 26, 2008, 12:05 PM
    Clanking Gas Furnace
    Why does my gas furnace clank right before blowing the air when it comes on?
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #2

    Sep 26, 2008, 02:44 PM
    Good question and sorry to say I cannot hear it from such a long distance.

    I would check the blower assembly for the furnace.

    Bad rubber mounts,bad motor belly mount or welded arm assembly (depending upon the style you have) can cause this type of problem. A loose cage setting screw can also allow the cage to slip on the shaft and due to play in the shaft can cause a scrape type sound.

    Best to pull the assembly and perform a inspection. While you have it out you might as well disassemble and clean. I am sure the cage blades are dirty.
    mygirlsdad77's Avatar
    mygirlsdad77 Posts: 5,713, Reputation: 339
    Plumbing Expert
    		  
    #3

    Sep 26, 2008, 04:25 PM

    Are you sure it is right before the blower comes on, or is it right after. Is it a new problem or has it always done it. It may just be your ductwork popping. Does it also make the noise when your blower turns off? If its not your ductwork, then follow hvac1000's instructions. Ductwork popping will usually sound more like a drum.
    sharonbb's Avatar
    sharonbb Posts: 3, Reputation: 1
    New Member
    		  
    #4

    Sep 27, 2008, 09:39 AM
    Quote Originally Posted by hvac1000 View Post
    Good question and sorry to say I cannot hear it from such a long distance.

    I would check the blower assembly for the furnace.

    Bad rubber mounts,bad motor belly mount or welded arm assembly (depending upon the style you have) can cause this type of problem. A loose cage setting screw can also allow the cage to slip on the shaft and due to play in the shaft can cause a scrape type sound.

    Best to pull the assembly and perform a inspection. While you have it out you might as well disassemble and clean. I am sure the cage blades are dirty.
    This didn't start happening until I had the furnace cleaned and inspected in early spring. It is not the ductwork popping. It is loud clanking and squeaking and it never did this before.
    sharonbb's Avatar
    sharonbb Posts: 3, Reputation: 1
    New Member
    		  
    #5

    Sep 27, 2008, 09:43 AM
    Quote Originally Posted by mygirlsdad77 View Post
    are you sure it is right before the blower comes on, or is it right after. is it a new problem or has it always done it. It may just be your ductwork popping. Does it also make the noise when your blower turns off? If its not your ductwork, then follow hvac1000's instructions. Ductwork popping will usually sound more like a drum.
    Thanks for the info. It is not the ductwork popping. It just started after having it cleaned in early spring. It does not make a noise when it shuts off.
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