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I am remodeling a basement bonus room; am adding a closet. The main ductwork was enclosed in a soffit. Due to the placement of the closet, I'm enclosing the soffit within the new closet header.

The previous register (10X6) is now removed and I'm left with a rough opening the same size. I am looking to source pieces that will allow a straight extension of approximately 15"; I would also like to reduce the register down to 10X3.5 since the room typically overheated/cooled with the large opening. In the image, you can see the frame for the original soffit.

I'm searching websites and cannot find any simple solutions.

Rough opening of the main duct

isherwood
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user187622
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3 Answers3

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Whatever you do will require some sheet metal work, either by you or others. For DIY, the transition from rectangular to square is the most difficult part of the fabrication. You would cut two 5" holes in a flat sheet and cut to cover the existing hole. Buy a pair of readymade $10 5" duct flanges and use sheet metal screws to mount them to the flat ductwork, sealing the edges with duct tape. That gives you two 5" round outlets that you can extend with standard duct, fittings, and diffusers. (You could send them different directions, and put dampers in the straight section to control airflow.).

MadMonty
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This can be done fairly easily with just a new rectangular duct cut to fit.

  1. Procure a new rectangular duct in your desired size. It should be as long as your extension will be plus several inches.

  2. Make cuts along the corners at one end to create 2-3" tabs across the duct sides. Bend these 90° outward from the original position. The need to be large enough to overlap the trunk duct adequately outside the hole. It may work best to make two cuts at each corner, just on either side of the fold, to eliminate the fold. You should now have an assembly akin to a stovepipe hat.

  3. Test fit your extension. Optionally place additional bends in the upper and lower tabs to wrap over and under the trunk. These will now be in a Z configuration. Bend the original tabs on the trunk or remove them if they're in the way.

  4. Use pure silicone caulk and sheet metal screws to seal and attach the extension to the trunk.

The secondary bends above and below the trunk aren't strictly necessary, but screwing the extension to the duct on four sides would make the connection much more rigid. You could also just use tabs on the sides for fastening and use a support elsewhere on the duct instead, such as at the outer framing. Do leave top and bottom tabs for proper air sealing, though they could be shortened to just lap the trunk duct completely.

To make these bends it's helpful to have some scrap lumber on hand. By bending against the corners of the board or even clamping the metal between two boards you can more easily make straight, square bends.

isherwood
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As a DIYer, not an HVAC pro, feel free to take this with a grain of salt. (Also, hopefully I understand your problem.) I don't think there's a standard part that will work for you to convert a 10x6 opening to 10x3.5.

First, I'd move that framing member on the left over to the other side of the joist, if possible, to give you additional working room.

It looks like you have a couple of tabs on the sides of the existing opening. I'd cut these to fit the new 3.5" height, then bend flat the parts that won't be inside the new duct. Screw your new 10x3.5 duct to the tabs. Then get a couple pieces of sheet metal (perhaps leftovers from shortening your new duct) and bend them to cover the remaining holes, with tabs you can attach to the top and bottom of the new duct. Then screw it all together and cover the edges with aluminum HVAC tape.

Huesmann
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