Modifying the air return duct?


Hello,
We're currently redoing our kitchen in a 1000sq ft., two story townhouse, and thinking about removing about couple cubic feet of duct.
I'll try to explain it as best I can:
Our air return duct goes straight down from the 2nd level to the basement, at mostly the same dimensions the entire length. However, once it gets near the kitchen floor, it increases in depth from about 12" to 18", and continues at that depth until it hits the furnace. On the opposite side of the wall (living room) is a return vent, and this is where the dimensions change. The return vent is about 6" wide, and the ductwork is about 8" wide- no problem there- but at this point it goes from about that 12" depth to 18". I was wondering if this is done for any particular reason, because we'd like to remove the extra depth in the kitchen area to allow for a cabinet. The return would only be modified for about 2 feet, and the rest of the return would remain intact.
Is there generally any things to watch out for, or does this seem like a non issue? Also, I'm fairly handy, so it seems simple enough to take a saws-all to it, patch it up with the (now detached) sheet metal, and tape it up. Am I missing something?
thank you!! Frank
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While it sounds simple, trying to cut a sheet metal duct with a saws-all will be difficult and result in quite a mess of razor sharp edges. Re-assembling it as a smaller duct will be just as much a problem as the metal will be bent and hard to seal especially at the back, the raw edges will become a lint trap and start gathering dust bunnies and dust reducing the airflow. Either have a new duct made and installed or try to work around what you have.

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EXT wrote:

A saws-all is definitely the wrong tool for the job, but it should be possible to fabricate something with a pair of snips and maybe a nibbler.

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CJT wrote:

The reason the duct gets bigger at that point is because it now has to handle not only the air from upstairs, but also the air from the additonal vent in the room on the other side. Can you get by though, by making is smaller? Perhaps, depending on how many other returns there are. One possibility I would consider is blocking off the downstairs intake if there are enough alternate downstairs intakes. That's because having adequate reutrns from upstairs is a big issue in summer cooling and if you cut down the duct size, but leave the same number of vents, you're going to lose some upstairs intake.
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You really need advice from a HVAC contractor............
modifying your ductwork will likely lead to poor performance....
trust me you dont cant cut ductwork with a sawzall. everything just bounces around with lots of terrible ear shattering noise.
unfortunately i have first hand experience in this area:(
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