Need help quickly too!!

I did a Inspection on a 4000sq ft mid 1800’s home. Everything was completly re-done better than new home construction. My question is with the return duct in the basement. I can’t for the life of me remember why a galvanized duct will “bang” when the fan comes on. I haven’t seen or heard this is several years. I can’t find any info in my books or online if it’s oversized/undersized duct work, lack of return vents etc. If any one assist could help before I send this tomorrow morning it would be greatly appreciated.


Just say the duct bangs and refer it to an HVAC specialist. You don’t have to know the reason why.

Was the filters restricted/dirty or too small of a return vent for the unit. The negative pressure on the duct makes it buckle and that sounds like a bang. If the return is a system of return duct throughout the home one section may be crushed or the return vents closed.
Joe has a good point

Thanks David. Joe If I had to refer everything I did not know an answer for what is the purpose of people hiring me. Don’t take it the wrong way, because I understand what you are saying, however I like to understand how every systems work “if I can”. It could be electrical, plumbing roofing or heating. Every time I can learn some thing new I can pass it on to someone here on the board.

Just some thoughts! Again I always will refer it to someone if I need too!

Thanks again,

Many times square metal ductwork will be ‘creased’ with a brake during the mfg process to give large, flat areas a little rigidity. This will help eliminate the banging when the air handler comes on and reduces the pressure in the duct. I suppose a reinforcing plate or strip could easily be attached to the offending piece of ductwork if it can be located.

Good post Michael - Sometimes a well placed strip of aluminum or duct tape will silence the offending duct.

Thanks Bill and Michael… I will pass along the information. Learned something new today! Have a great weekend.


Sure, no problem. Here’s a picture of a hand brake if you’ve never seen one. It’s used to bend sheet metal and they are quite large & weigh around a ton or more. Not a field tool!

Sorry Michael…When I had my HVAC installed I had 120-feet of metal duck work “Creased” by the installer while he was “set up” in my 2-car garage.

Well, smack me down…thanks for correcting me, here’s a tribute in your honor: clickherebutton.gif](