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New A/C Duct

Posted by phillipeh (My Page) on
Thu, Oct 22, 09 at 10:34

Has anyone ever run a new a/c duct? For some reason, our contractor's HVAC sub didn't put a/c outlets in two walk-in closets. (I asked why and he said they weren't on the plans. He could do it, at a cost of $200 each.) One closet doesn't seem to matter, but the other is on a corner of the house exposed to afternoon sun and it gets rather warm in there. The attic and existing ducts are readily accessible, but I just wondering if it's a hard job, as in hard enough that I should hire a professional. Thanks!

Follow-Up Postings:

RE: New A/C Duct

Phillipeh - It's really easy to do, and you can get the materials from

Here's what you need -

part # 5078k111 self-sealing collar
part # 1844k14 90 degree register boot
part # 55315k72 6" flex

Hope this helps,


Here is a link that might be useful: Here's a good article for ya

RE: New A/C Duct

The issue is the balancing of the system if you add an opening in an existing duct. You can really mess up an HVAC system, assuming it was ever balanced in the first place which is rare in my experience. Can the room return air duct be moved to the closet?

RE: New A/C Duct

Um, yeah, about the balancing thing: that never happened. We have three 2 ton units for a 3029sq ft house. One is for upstairs (about 700 sq ft), one for the master suite (about 600 sq ft) and one for the "main" area of the house (about 1700 sq ft). Anyone who can explain THAT? As it was explained to me: instead of a 4 ton unit for downstairs, I would need 2 2ton units because it was just "impossible" to get ducts all the way across the house to the master suite AND get any type of air flow WAYYYY over there. Fortunately, the house is comfortable, we only have to run the a/c unit for the master at night, and our last electric bill was $109.

I just want to add a vent to that walk-in closet because it gets so warm. What exactly is a "room return air duct?"

RE: New A/C Duct

You have multiple units for a couple of reasons -

1. In a multi-level house, there's always a temperature difference between floors.
2. A 4 ton unit would require large supply and return ducts. Locating them in a wall, crawlspace, or attic can be almost impossible sometimes.

Attach the collar (takeoff) onto the main supply duct for the particular unit for the area, and run flex over to the boot that will be located in the closet.

I'm not gonna get involved in the whole "balanced system" thing, but just remember that adding another run will effect the airflow velocity of the other vents.


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