Friday, 19 February 2021

Very loud banging and popping in one specific vent, any way to fix this?

I live in a 27 year old home in Southern Ontario, Canada. Temperatures are similar to the Midwest in the US, cold winters and hot summers. We have both central air and a gas powered furnace. In September 2020 our AC broke and we decided to get a new AC and Furnace at the same time, as the furnace was 27 years old and had a few issues. Got a good deal with a good warranty so went for it.

Now the problem I have been dealing with is that a specific vent is expanding and contracting and causing very loud popping and banging sounds when the furnace comes on and off. It also sounds like 2X4 wood in the walls is making similar noises. These noises didn't occur this loudly before.

The furnace they installed was 60,000 BTUs and the original one was 80,000 BTUs. They said it was oversized and the 60k one would be better. I had one of their techs out the other day and he took a look down the vent and noticed that it is round duct work that has been squished to fit in the wall and is compromised. He said this is the reason I am hearing the noises, the joints are compressed and not tight, and air would also be leaking into my walls drying out the wood (I do not have a humidifier, but humidity sits around 35-40 in the winter).

He tried adjusting some settings on the furnace, to make it blow slower but hotter, but this caused it to give an error, so he went back to the original settings.

I guess I am at a loss as to why this would be making so much more noise now, and not before? The ducts have been this way for 27 years, all they did was install a new furnace. Is there anything I can do to make this quieter? It is driving me insane, we can hear it all on the main floor and the vent hole is right into our on-suite bedroom bathroom so I hear the popping all night. Other than ripping apart all my walls and installing new ducts, what options do I have here?

A user on reddit suggested that the furnace is heating up the vents too much now and to actually adjust the fan to go faster. Here was his response "Your 80,000 btu furnace at 27 years old would be approximately 60% efficient, therefore heating output to the ducts of approximately 48,000 btu Your 60,000 btu furnace will be 95% or higher efficiency, therefore at least 57,000 btu All I other factors being equal, the new furnace will put out 9000 btu extra, ducts heating up more. Additionally the heat rise may be too high, so the fan should be sped up more to lower heat rise"


source https://hvac-talk.com/vbb/showthread.php?2226785-Very-loud-banging-and-popping-in-one-specific-vent-any-way-to-fix-this&goto=newpost

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