Central Air -- In-duct fan to help push the air - is there such a thing?

We just replaced the Central Air system (including the furnace). Nice powerful blast which rapidly drops the temp. on the first floor.
The second floor is a slightly different story. I was expecting a more powerful flow there. (tho it's certainly much better than it was with the old unit) I wonder if anything could be done to improve this. What was a little unusual, tho, is that the master bedroom had a stronger flow than the 2nd bedroom. The vents are essentially back to back, sharing the same wall.
I crawled up to the attic to inspect the vents and discovered the reason for this. The tube comes up to the attic where it hits a Y connector. The master bedroom's tube comes off this in a straight line while the 2nd bedroom's goes up and around. This upwards slant also feeds the shaft to the office and two bathrooms, all of which have lessor air flow.
I wonder what can be done to improve this. First thought is to completely redo the layout up there so all the venting is flat on the floor. My next thoght is to insert a fan in the tubing to help propell the air along. Do they make such a thing? I'd image the airflow would spin the fan which would force the air thru faster thus getting a stronger flow to these rooms thus cooling off the upstairs faster.
Any other suggestions?
-Otter
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They do make the inline fans (available at Home Depot) but I haven't heard a lot of good things about them. I would focus on the ducting. You mention that they are in the attic: are the ducts insulated? Second, have the installers back to balance the system. Sometimes closing some first floor vents can improve flow upstairs. Also look for separations in the ducting going upstairs.

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a
I have one for one room, it for it, it worked. Someday I will correct the venting problem that caused the problem to begin with and get rid of the fan. In another situation it failed totally. That one has a more serious duct problem, it has a serious block in a area that is very difficult to get to.

In addition it may be possible (likely from the description the orginal writer gave) that the distribution (supply and return) systems are poorly designed and need to be changed.

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thanks for all the comments:

Well, this is your simple design californian home. Only two vents exist on the first floor. One is in the same wall shared with the furnace/blower, and the second is a few feet away in the living room. The furnace is in the garage. The two bedrooms upstairs are above the garage. There is nothing above the rest of the rooms on the first floor (which isnt exactly true as we built a new room above the dining room and kitchen but I'm ignoring that).
The path of the vent seems to be between the two floors to the living room. Somewhere in that path it must branch off below the floor a short way, where it goes up the 2nd floor wall to the attic where it branches off four ways (2 bedrooms and bathrooms).
I had intended to climb down into the crawl space behind the wall on the 2nd floor and replace as much of the vent as I could but it's much smaller than I imagined.
So: Closing the two first floor vents really doesn't do much. It occurs to me as I write this that I could block one off completely - the one closest to the blower. The dining and living rooms are wide open to each other so this would not affect cooling the downstairs much, if at all.
And yes, everything is insulated. From the part of the system that is visible I could not see any leaks.

This was my thinking which is why I wondered about an in-vent fan to help propell air through the system.
I asked about zoning as a coworker did this and recommended it. The contractor recommended against it for various reasons: break down easily, air flow can be just too powerful (ie: 3 tonne fan pushing all the air to just two vents rather than even distribution), etc.
They're coming back this week to look at a problem with the AC unit (it emits a high pitched whine shortly after it's been turned off), so i will ask further about the airflow.
-Otter
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Since you have a 2 story house, you may want to consider zoning it.
Air is lazy and flows the easiest way. That's why the DS is getting more airflow.

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Otter wrote:

sounds like that is the trouble you need the duct fan to give you more air floor into the rooms that dont get it or you need the downstairs vents closed more to give more force to the ones upstairs that dont have as much air....
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In alt.home.repair

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A proper manual D duct calculation, before the installation wouldhave helped, and a tech that did the installation that knew what he was doing would have helped out alot as well... Duct fans, are garbage. There is no problem with air flow that can not be fixed in some fashion without one. Do not use them...have a compretent tech out to access your current situation, and go from there.
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This is Turtle.
No your wrong here, he invented Electricity and along with copper pipe fuses in the place of regular fuses and Regular PVC pipe sch. 20 to vent gas hot water tanks with.
He is a very remarkiable person.
TURTLE
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