I have a typical 2 story, 4 bedroom house, which is served by a single HVAC system.

Air flow upstairs is reasonable with the exception of one bedroom, which is my computer/radio room and serves as a spare bedroom.

That bedroom and a next door bathroom are each provided with a single 6" run/register. The run to the bedroom is approximately 24' longer than the other. The bathroom has plenty of air and no adjustment of the damper seems to help.

The runs originate 2' (bedroom) and 3' (bathroom) from the trunk/plenum junction. So far, I haven't been able to find the 'sweet spot' by adjusting the two dampers. I would have thought that the bedroom being first in line, would have the greater air flow. Wrong?

Might one of those squirel cage duct fans help? Any other suggestions?