I recently bought a house with a forced air heating system. I am interested in any tips or ideas anyone might have to quite the ducting and vents as much as possible. I have one section of large rectangular ducting on the return air loop that the sides expand when the system shuts off, making a large banging noise. Aside from that, i believe the noise isn't anything out of the ordinary, just looking for any ideas on quieting the system in general.
Congratulations on the new home. Expansion is common in sheet metal ductwork with the changes in temperature. One way to minimize the banging is to stiffen up the material. If you look at the new prefabricated material in stores, the wider pieces have creases in them to stiffen them up (and prevent flexing with associated noises).
So how can you stiffen up your existing sheet metal? The most professional way to fix the problem is to have a sheet metal contractor come out. But if you don't want to spend the money and are willing to try something unconventional, you can try putting a few slight dimples in the sheet metal at the noisy location with a hammer. Make sure you don't make deep dents as these will disrupt the airflow and make your system inefficient.
Good luck to you.
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Go to Home Depot, Menards, whatever and buy some "S" cleat in the ductwork section. On your duct at home lay the "S" cleat diagonally across the duct making noise and screw it to the duct, or use some lite weight angle iron drill holes in it and screw that to the duct. Usually when a duct (probably the return, I'm guessing) makes noise like that it means that there is not enough return air to the furnace. Make sure that your return vents arent blocked (or closed if they have a damper in them. They shouldn't btw). You might even want to add a return in the basement (away from the furnace or water heater).
Good points above. Also, if you have an air conditioning coil in the plenum above the furnace, check to see that the blower is operating at the right speed - low. The high speed is for cooling or "fan on" at the stat. Older blowers used wire nuts, newer - spade clips, and newest are connected to different spade terminals on a printed circuit board.
I think there is a standard color code to select speeds. You might also measure temperature rise across the heat exchanger to determine whether to use the low or med. spd.
The lower spd. will also reduce noise.
Tom from CT.
HVAC/Refr Mechanic since 1980
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