What causes a knocking sound in my furnace duct work.

  4 answers
  • Joseph Glackin Joseph Glackin on Dec 31, 2017
    Heat. As the furnace sends out heat, the joints expand and knock. Check the flues are secure and not dangling loose. Consider tightening them and maybe insulating. That should also make them more efficient.

  • Dfm Dfm on Dec 31, 2017
    my duct work has been much quieter since i used a foil tape and taped all the joints. it's warmer air getting to me now.

  • Lyn2398900 Lyn2398900 on Jan 01, 2018
    Somebody want's to get out! If you have furnace ins. they will find out. Best ins. we've had. Twice a year cleaning goes with it, everything, the parts, etc. included in the ins. Something to think about.

  • William William on Jan 01, 2018
    Joseph is correct. As the ductwork warms up it expands and travels. The sound is also amplified Try to trace the location of the sound and do what Dfm suggests. Use foil tape the seal all joints Insulating the ducts will also help.