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  1. #14
    Join Date
    Oct 2007
    Location
    Midwest
    Posts
    194
    erc tech brings up a good point, but the noise would be a one time pop when the fan stopped, and not last several minutes.

  2. #15
    Join Date
    Feb 2006
    Location
    Tn.
    Posts
    1,344
    try to isolate the problem most of the tine in the return line When the air shuts off its kinda like crushing a coke can let off and it pops back into place. try putting bricks in your return if thats where its poping.

  3. #16
    Join Date
    Aug 2007
    Location
    Chicago
    Posts
    20
    I ran the heat again, and I can hear the knocking noise in the ducts on the north end of the 3rd floor, but not on the south end. Another thing I noticed is that the air flow is much lower on the north side ducts than on the south side ducts. Could this be related?

    I would like to clarify that it is not a one time pop. It's a knocking or tapping noise that occurs every 5-10 seconds for a few minutes.

    I appreciate all your help

  4. #17
    Join Date
    Dec 2003
    Posts
    709
    It is caused by the ductwork heating up and when it cools off it contracts and pops. This is why it doesnt happen in cooling mode. You may be able to have tech increase fan speed for heating. Have a service check done and see if anything can be done. If you can take a temperature of the air in the duct before and after the furnace and report findings.

  5. #18
    Join Date
    Aug 2007
    Location
    Chicago
    Posts
    20
    Quote Originally Posted by hivacer View Post
    It is caused by the ductwork heating up and when it cools off it contracts and pops. This is why it doesnt happen in cooling mode.
    I used to rent a different townhouse in the same development with the same exact layout, and the ductwork didn't make this noise. Why would it happen in the place I just purchased?

    I've been very disappointed with my "new" place. First, the AC made a horrible noise, and I had the subcontractor who installed the system 4 years ago come out, who said the compressor needed to be replaced. They replaced the compressor, which didn't fix the noise, and then Carrier came out and found a kink in the suction line. The HVAC subcontractor tried to blame the siding subcontractor for the kink...

  6. #19
    Join Date
    Dec 2003
    Posts
    709
    I have seen it happen when the heat was oversized. Do you have the model # available for the furnace? Maaybe your other place had a smaller btu output in the furnace, or the fan speed was set different.

  7. #20
    Join Date
    Aug 2007
    Location
    Chicago
    Posts
    20
    Quote Originally Posted by hivacer View Post
    I have seen it happen when the heat was oversized. Do you have the model # available for the furnace? Maaybe your other place had a smaller btu output in the furnace, or the fan speed was set different.
    How do I find out the model #?

    It's the same system as in the place I was renting, but there is no setting for the fan speed. How is that set?

    How can the heat output on the 3rd floor be balanced?

    thanks for your help

  8. #21
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by dash View Post
    After a long run time,stand near the furnace and listen to see what you can hear.
    Did you try this???

  9. #22
    Join Date
    Jul 2005
    Posts
    717

    Smile

    Dash says .....stand near the furnace and LISTEN TO SEE WHAT YOU CAN HEAR"......
    Now that's a real statement (lol) and it would be quite a trick if a person could actually do this..

  10. #23
    Join Date
    Apr 2005
    Location
    Kingston Ontario Canada
    Posts
    1,234

    noise in ducts

    Quote Originally Posted by beethovengirl View Post
    This is the first time that I've turned on the heat in the home I recently purchased, and after the furnace shuts off, I can hear a knocking noise in the ductwork that eventually stops after a few minutes. It is a Carrier split system with a gas furnace. Do you have any suggestions on what might cause this and how to fix it? thank you
    Hi beethovengirl: I have ticking noises coming from my ductwork, too! It's just the metal in the ducts heating up and expanding slightly, and then cooling down and retracting. It's nothing to worry about, unless it really bothers you. But is not hurting anything or equipment malfunctioning or anything like that. Sometimes if on installation the ducts are too tightly installed agaist the floor joists and the ducts closest to the heating appliance get warm this can cause some noise from the wood in the floor joists.

    Thorton

  11. #24
    Join Date
    Nov 2005
    Location
    sacramento calif.
    Posts
    1,191
    b-girl, no one here can tell what the noise is. it could be anything from "tin canning" which could be a good thing telling you your filter is dirty to the edges of a gapeing crack in the heat exchanger scrapeing against each other as they heat & cool. the length of time you describe & it being at the end of the heat cycle make me lean towards the latter. call the guy.
    i was born under a wandrin star.

  12. #25
    Join Date
    Oct 2005
    Location
    phoenix az
    Posts
    429
    Quote Originally Posted by beethovengirl View Post
    I don't understand your reply, skorepeo. Is my post considered trollish?

    hey just funnin

    but really it is rather difficult to explain noises unless I was right there at the time of occurrence

    but heat applied to metal expands it and some metal expands at a different rate than others therefore if the duct system has fasteners that are loose or made of different type metal they can make noise as the ducts are heated
    and again as they are cooled
    "Do not let what you can't do interfere with what you can do"

    "Do what you can do the best that it can be done and no one will ever know what you can't do"

  13. #26
    Join Date
    Dec 2007
    Posts
    4

    Low Air Flow - Ductwork noise

    I'm having the exact same problem. When several people said that it might be the ductwork fastened to tight but then the guy stated that the vents where he hears it have much less airflow.

    That is my problem as well. Could the low airflow and the sound be related?

    John

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