What happens to airflow in plenum box that remains


Old 08-20-20, 02:13 PM
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What happens to airflow in plenum box that remains

Down Stairs plenum box to be converted to a system of duct WYEs You can see its feed by zoned damper

I purchased a rectangular to round transition for the output of my air handler
There are two 14" holes instead of one
so the rectangular transition goes to two holes

one hole feeds a zoned damper to a dedicated plenum box to supply air for upstairs rooms
one hole feeds another zoned damper to a dedicated plenum box supply air for the downstairs rooms (attached picture)
so the air is jammed to the back of the plenum boxes and its forced to go out the sides of the box.

If I change out the downstairs plenum box to WYEs to reduce static pressure on the system.
I still have the plenum box for upstairs.

What would happen to my air flow? Would more air go to downstairs now?
Ideally I would change both of these plenum boxes to WYEs at the same time.
But the upstairs plenum box and its ducts make is more complicated than swapping out the downstairs plenum box.

So after converting the downstairs plenum box to WYES, I'll have:
1) One feeder goes to the upstairs plenum box
2) other goes to WYEs instead of a plenum box.

Its not balanced and Im wondering how much impact it would create?

I really dont want to convert both plenum boxes to a system of WYEs yet.
I want to do downstairs first, then upstairs.

thanks alot

Old 09-05-20, 02:39 AM
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Join Date: Jul 2020
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I don't think you can hurt that - forgive me - mess a bit. Do provide a good manual balancing damper where the other box was, to replicate its pressure drop so you have the same flow at the remaining box. Duro-Dyne has many
applicable products, the damper itself should be similar to their "Heavy Duty Jiffie Damper" with 22 ga blade and continuous shaft. The damper will have to be installed in round duct, not flex.

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