Duct Reduction - How to Install a Ductwork Reduction taper - PlumbersStock.com

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Phillip Green of PlumbersStock.com fame demonstrates how to reduce a ductwork from a 14" diameter to a 12" diameter. Using correct reductions in your vent work is important as it will help to ensure that the air pressure exiting your ducts is uniform throughout all the vents in your home.

Video Transcript:

This is my taper from 14 to 12 and since it doesn't quite fit just right, doesn't go over it, it's about exactly the same size. So I'm going to use this crimper, it's a Malco C3 and put the double blade inside and the single blade on the outside. And it will actually change the diameter of the pipe and depending on how hard I crimp it and how far apart they are it will bring it in more. I only need to come in about a 1/16 of an inch to get this bell-roster over it, or taper. So I'm going to go about ½ and inch apart and I probably won't even go around the whole thing, just part of it.
I'm going to give it a try...Beautiful.

That will make a good seal once I screw it in place and put the duct sealant on it.

Alright, I got the bell-roster on now and before I'm going to pookie it, I want to put the next piece on so I can seal them together. It's called pookie, the duct sealant. That's the technical term.
Here's the crimper, see on one side it has two blades, on the other it has 1. They actually make one that has three blades on one and two on the other so that you can go even faster, but it doesn't crimp as deep. So if you need to resize the pipe too much it won't work. So once again, the more blades go on the inside of the pipe for a better crimp.

To hang my piece of 12 inch, I've hung this strap right here at an approximate height and then I'm going to bring the spiral pipe in and through it, just to support it so that I can attach it on to my bell-roster. Once it's in place then I'll level it off and adjust the strap as needed.

There we go.

The reason why we reduce the size as it goes through is because as we take off registers and more air, the static pressure will decrease. And you want to keep that static pressure usually around .1 (point 1) on a duct system like this.