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Old 10-07-2008, 01:39 AM   #1
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Need to extend an HVAC return trunk...


an additional 32". What's the correct way to do this? It's an odd size of 8 x 19 3/4 with a spot welded cap at the end. I'ts needed to maximize additional air return.

Any good do it yourself books out there on HVAC duct work?

Thanks for any help for the noob.

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Old 10-07-2008, 04:44 AM   #2
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Need to extend an HVAC return trunk...


A spot welded end cap is unusual. Can you elaborate? Is the rest of the duct spot welded also, or do the other seams have S&D's.

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Old 10-07-2008, 05:08 AM   #3
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Need to extend an HVAC return trunk...


Only the ends of the trunks for supply and return are spot welded and I may not be using the term cap correctly in this case. The rest of the trunks and branches are some type of seam. I'm not familiar enough with them to tell you which one. I can post a pic if it helps. I thought I could just make a clean cut or just knock of the spot welds if that works, but I'm unsure how to make the connection for the extension.
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Old 10-07-2008, 05:22 AM   #4
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Need to extend an HVAC return trunk...


Most ducts are connected using "S" locks and "Drives. The S locks seal and stabilize the horizontal edge, the drives are vertical locks that slide on tracks at the ends of each piece of duct to draw it together and seal the duct, then folded over to keep them from sliding off.

If the verticals dont have the tracks folded over to allow the drive to be slid on, measure that piece of duct and have a new one made up along with the extension. Bend the ends up, grab the drive with a pair of channellocks and hammer it off. It should slide off.
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Old 10-07-2008, 12:09 PM   #5
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Need to extend an HVAC return trunk...


More than likely you have an 8x20 which is a common size. If you can get the cap off they you can probably add a piece on. Even if the measurement is 19 3/4 it is close enough to connect an 8x20.

As 8 Ball says most are connected with S lock or drive/hammer lock so a spot welded cap is unusual.

Pictures would be good of course.

Here is a good video of S lock and drive lock (they call it drive cleat, same thing).
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Old 10-07-2008, 02:31 PM   #6
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Need to extend an HVAC return trunk...





This is the end cap of the return trunk.

The other pic is of the same end cap and the old return grill that I want to hook up again.

If I understand you guys correctly, I can remove the end cap, place an S-lock on the horizontals and create the "flaps" by hand for the drive lock on the verticals and then add the new 8x20 section.

What's the best way to build a new 32" section of 8x20 trunk? Can I just purchase a 4' whole section?
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Old 10-07-2008, 03:43 PM   #7
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Need to extend an HVAC return trunk...


I know what sections I need and am confident enough now to connect.

How much would a sheet metal shop charge for the pieces?
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Old 10-07-2008, 04:28 PM   #8
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Need to extend an HVAC return trunk...


Quote:
Originally Posted by 8 Ball View Post
A spot welded end cap is unusual. Can you elaborate? Is the rest of the duct spot welded also, or do the other seams have S&D's.

A lot of shops used to spot weld the return pressure plate in place.

But those pics aren't of spot welds. Those are swaged ends.
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Last edited by hvaclover; 10-07-2008 at 04:35 PM.
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Old 10-07-2008, 04:37 PM   #9
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Need to extend an HVAC return trunk...


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Originally Posted by Sylvester2 View Post
I know what sections I need and am confident enough now to connect.

How much would a sheet metal shop charge for the pieces?

No way of knowing. You have to check a local guy. Prices are different around the contry.
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Old 10-07-2008, 06:52 PM   #10
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Need to extend an HVAC return trunk...


8x20 is a common size. I use it all the time and you can get sections of 3, 5, 8 and 10 feet. They come in halves and you just snap them together.

Just looked at the Gensco catalog and they are about 15 per 5 feet. I am not sure if that includes both pieces or not.

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