Need help quickly too!!

[Christopher Rich Iii]

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.

Thanks,
Chris

[Joe Funderburk, CMI]

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

[David K. Smith]

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

[Christopher Rich Iii]

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,
Chris

[Michael R. Boyett]

Chris,
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.

[Bill Smith]

Originally Posted by mboyett

Chris,
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.
Attachment 8336

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

[Christopher Rich Iii]

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

Chris

[Michael R. Boyett]

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!

[Frank M. Carrio, CMI]

Originally Posted by mboyett

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!
Attachment 8341

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.

[Michael R. Boyett]

Well, smack me down...thanks for correcting me, here's a tribute in your honor: