Cracking noise associated with furnace operation

Old 12-02-12, 05:57 PM
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Cracking noise associated with furnace operation

Hello All:

The past several weeks I have been experiencing a loud popping noise that coincides with the beginning and ending of each furnace cycle. During the cycle itself, which is somewhat brief, there is no popping/dripping noise at all. By that I am referring to the time once the air gets up to max temperature.

I convinced myself that it was coming from an interior wall in only one room of the house. The wall in question has some rigid ducting running through it for our downstairs system. The duct is encased in a metal sheathing within the drywall.

I called a handy man that is quite capable and has worked on our house several times. Over the past three days we have worked the problem and each time when he leaves the popping noise is eliminated only to return overnight/early the next morning when the unit is programmed to warm the downstairs. He thinks that the metal sheathing that surrounds the ducting was not secured properly, is expanding and contracting as the air heats and cools throughout the cycle. His remedy has been an attempt to tighten the sheathing to the drywall by inserting metal screws into it through the drywall. Luckily, the backside of this area happens to be a wall in the attic so nobody can see all these screws. I will mud and paint over them once the issue has been resolved.

However, today, after reading several postings on this forum, and hearing the noise in another room, I did some additional investigating in my attic at the furnace itself. What I found was that the noise is either coming from the vent pipe or the box on top of the furnace where the air is being sent to the duct work. The noise is then being transmitted through the ducting. The ducting from the furnace starts out by running down into two interior walls of the only two rooms of the house that I can hear the noise.

The noise is quite loud, loud enough to wake me from sleep. Can anyone recommend what I can tell my handyman to try to do to fix this issue? He is happy to work the problem but, he just doesn't know what to do next and neither do I. Is this an issue for an HVAC guy or is there a correction that he can make for me?

Thanks for any input - Seess
Old 12-02-12, 06:06 PM
Join Date: Nov 2012
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Not enough cross break on the duct or maybe the duct isn't a heavy enough gauge? Bang when the furnace blower starts and bang when the blower stops?
Time to get out the big hammer lol

Actually, you can add a piece of metal or a standing S-Slip in the duct joint to stop this.

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