Question: Why would the 6" duct (represented by the red X) produce almost zero airflow?
I have a small piece of tissue attached to it to see that it's barely blowing anything. However, the blue arrow, which is a vent that's further down the path, is getting plenty of airflow.
All of the blue arrows represent good flow.
And...as I write this, I just though of something.
The bottom blue arrow leads to a bedroom that's attached to the bathroom and it's at the end of the main HVAC duct, which is much larger in volume than the 6" branch feeding the bathroom.
In essence, both ducts are feeding the same space, and since one is larger, would it be safe to say that the larger duct is causing static pressure that's basically squashing the 6" duct's output?
There are no return ducts in this house, just the single intake for the A/C.
It would seem that if two ducts that are different sizes feed the same space, one would overpower the other, or there'd be some sort of way to predict the flow out of each depending upon the volume of the branch...
I'm wondering if the only way to equalize the flow is to ensure that the output volume on both is the same by adjusting the registers.
I also suspect that the the 6" take-off is too close to the A/C unit's output. It's a roof mounted unit and the take-off for this branch is right next to where the A/C unit feeds (vertically) the main HVAC duct (horizontal.)