On Jan 21, 1:42*am, blueman wrote:
The sheet metal return plenum on one of our 2 otherwise identical gas
furnaces gives out a loud "bang" as the duct contracts inwards when the
blower starts and again when the duct returns to its original
conformation when the blower stops.

The other furnace that doesn't "bang" seems to have a relief "X" on its
broad surface while the one that does "bang" doesn't have the "X".

The return plenum is 24"x8"x60".

I would prefer not to reduce the blower speed since the furnace is in
the basement and needs to provide forced air all the way to the 2nd and
3rd floors and the ductwork is highly non-optimal (the previous owner
had some hack do it with a maze of flex duct -- one day I will have it
replaced but not now...)

I have heard about people using "banding" to stiffen up the plenum and
reduce the movement but am not sure of the best way.

So...
1. What is the recommended way to eliminate such movement and "banging"?

2. If some type of banding is appropriate, what are the appropriate
materials and techniques to do it in a professional and neat manner?

THANKS!!!!

Go to lowes and get a small piece of angled iron or aluminum. Can be
1/2" x 1/2". Cut to fit diagonally, drill holes, and put some screws
into the sheet metal.