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Old 02-25-2011, 11:30 PM   #1
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Add new register from flex duct?


Ok...so I need to add a new supply register in the floor of a room I'm adding to my 2nd floor. I know that there is existing ductwork run in the floor directly below where I want my new register box. Here's the catch...the existing supply is insulated flex duct. How do I connect into this for my new supply point?

Any help would be greatly appreciated!

By the way...I know that tapping into this line will "rob Peter to pay Paul". However, given the size of the new room, I don't expect to be needing a lot of airflow.


Last edited by Vaneycke; 02-25-2011 at 11:40 PM. Reason: Adding disclaimer/thoughts
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Old 02-26-2011, 01:29 AM   #2
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Add new register from flex duct?


Probably wont work for sh!t, I would try to jump off the main supply instead. Where is the furnace located? Is the ductwork run through a crawl space or attic? Or is the duct all covered with sheet rock? The only way to jump off that flex duct is to purchase a 6x6x6 tee or wye, that size the hackers go-to so it should be available online somewhere. I do not recommend such a solution though, would rather help you to find the supply duct and come off of it.

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Old 02-26-2011, 06:07 AM   #3
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Add new register from flex duct?


Pictures and diagrams of the ductwork and sizes would help along with the location of the existing ductwork in reference to the location where you want to tie in.

I agree with uni I wouldn't but if you have to, find out the size of the flex and buy a tee takeoff (need room) cut the flex install the tee insulate it and run the open end of the tee to the register box. Not that easy without lots of room.
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Old 02-26-2011, 09:02 AM   #4
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Add new register from flex duct?


The furnace is on the 2nd floor, so the supply duct work for the whole house is all run in the floor. I have no way to access the main supplies without ripping half of my 1st floor ceiling out.

The first picture I'm attaching shows the supply trunk coming into the room. You can see that it has (2) 6" branches that feed the room.

The second picture shows a continuation of one of the supply lines. To the left is where it connects to the supply trunk. I would be connecting to it 1-2 feet after it turns.
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Add new register from flex duct?-ductwork_4.jpg.jpg   Add new register from flex duct?-ductwork_3.jpg.jpg  
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Old 02-26-2011, 12:33 PM   #5
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Add new register from flex duct?


Looks more like wrapped hard pipe on my monitor then it does like flex.

As long as the duct you add is only a 3" it might not take too much air from the other supply. And that room will only be a little too cool then.

Why not tap into the "trunk" that is feeding both of those current supplies.
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Old 02-26-2011, 02:03 PM   #6
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Add new register from flex duct?


Quote:
Originally Posted by beenthere View Post
Looks more like wrapped hard pipe on my monitor then it does like flex.

As long as the duct you add is only a 3" it might not take too much air from the other supply. And that room will only be a little too cool then.

Why not tap into the "trunk" that is feeding both of those current supplies.
Ok, so after reading your comment, I looked down the vent with a mirror and a flashlight. It looks like this is actually wrapped hard pipe. The connection for the existing register box is 6" round sheet metal.

In regards to the existing trunk, I would prefer to tap in there. However, that picture was taken before they put in the drywall (screwed and glued). Tapping in there would require ripping out about 15' of drywalled ceiling.
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Old 02-26-2011, 03:34 PM   #7
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Add new register from flex duct?


Then the room you steal the air from will be cold. Or you won't get enough heat to the new room, or a combination of both.
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Old 02-26-2011, 08:21 PM   #8
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Add new register from flex duct?


What I would do if I were you is cut access holes in the sheet rock. If you do it right you can have a couple of 14x4 holes (assuming the supply trunk and the new heat run location are in the same joist bay), one at the supply trunk and one where you want the heat run. So, at the trunk you would cut in a 6" saddle (this is a "tap" that your new duct will connect to) and at the other access you would cut a "4x10x6 90 boot" into the floor. Then you take a box of 6" "flex duct", and push it from one access to the other (it doesn't matter which one you start at) with a long stick or pipe or whatever. Connect the flex duct to the boot (or saddle) then pull out the slack, cut off the excess (leave it about a foot longer than the boot or saddle) and connect the other side, voilą!
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Old 02-27-2011, 06:47 AM   #9
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Add new register from flex duct?


Looks like a really nice place going to be there for a long time , why not do it the right way do a little sheet rock repair and have a nice system done right the first time to last for many many years even after your gone. Its worth it.

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