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Chimney Rumbling

gehring_2
gehring_2 Member Posts: 1
in THE MAIN WALL
One very cold days (and nights) when my boiler comes on for the first time after having been off for awhile, I can hear a tremendous rumbling in my chimney and the metal flue pipe and draft regulator/damper near the boiler vibrate and sound like their being shaken. This continues for 10-20 seconds and then the system seems to settle down, the rumbling noise stops and everything is fine.

I am wondering if someone can identify what is causing this vibration/noise. My layman's theory is that when the boiler has been off for a while the chimney will fill with cold air and then when the boiler fires its hot exhaust gases must fight with the cold dense air that has filled the entire length of the chimney (2.5 story)until the hot air wins and expels all of the cold air up and out...but this is only my guess - I am not sure. Can someone else explain this? FYI my chimney is interior to the building (not on an outside wall) and both the chimney flue and flue pipe from the boiler are sized right according to the boiler manufacturer specs. Thank you.

Comments

  • Ken_8
    Ken_8 Member Posts: 1,640
    After drip?

    Assuming you have an oil burner, I suspect a slight after drip. After drip is when the burner stops and a few remaining droplets of oil are expelled into the combustion area (or in the blast tube) and are not completely consumed by the glowing firebox - and upon re-ignition when a flame returns - it creates an artificially high oil to fuel ratio and voila - pulsing/rough combustion takes place.

    Air in the fuel line from a suspect fitting/joint can also create after-drip.

    The noise is almost certainly combustion related - and not chimney caused. The draft regulater may also be at play here - but I doubt it.

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  • Al Letellier
    Al Letellier Member Posts: 781
    rumble

    Good diagnosis on the draft issue. It certainly can be a problem. Only way to be sure is to use a draft gauge and monitor the draft during prolonged shutdown. If you don't have one already, any of the newer cad cell controls with pre-purge/post-purge can be a big help by establishing draft before ignition. Or you can try a delayed oil valve to accomplish the same thing.

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