Duct airflow problem

I think that maybe there is a damper somewhere that is restricting flow to some rooms and guess we need some kind of remote TV robot to insert in duct to find where it is. Anyone ?
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Look for dampers where the ducts begin or attach to the plenum. This is where I put dampers when I put in some new runs for my basement. The start collars are predrilled for the dampers already.
If you have exposed ducts in your attic or basement/ crawlspace then look for crushed or sagging ducts that have come apart at the joint(s). Kevin

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We don't have an attic or basement and the plenum just goes into the wall. We have a crawlspace under the stairs and lower landing but there obvious signs. The house is 50 years old. My next door neighbour has the identical problem. We've asked people who do duct cleaning if they can solve the problems but we've come up empty handed.

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This is Turtle.
You don't need a rebot to crawl duct because a good hvac man can size ducts from the outside and see baffles if you have them from the outside of ductwork. 90% of the time when a poster here says what you just said. the ductwork is jusy plainly too small but not being too bold 10% of the time it might be a problem like stopped up duct or a problem of some kind.
You start is to get a hvac man to run a manual D on your system and see if it is the right size.
TURTLE
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There are no visible ducts as we have no attic or basement in which to view them.

The air roars through in some of the rooms, whilst in others you can barely feel or hear it. The house is about 50 years old and my next door neighbour has the same problem, although there are some differences in the layout of their ducts.

Do you mean "manual diagnostic" ?? Size can't be changed easily.
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Can you be more specific ??
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Then you need an HVAC guy with a tool called the Inspector...its an infrared TV cam that is used mainly for checking for cracked heat exchangers.. However, if you find one, do not expect the check to be cheap.....about $150...those units cost an arm..

No..he means a ACCA Manual D duct size calculation....

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SURE...
First you need a room by room manual J, that gives you the total number of BTU per room, and then, knowing your states code on CFM and Face Velocity, at return, you need to find out static presure of the system, total, and then, determine the size of the duct, using the ACCA Ductulator, and Manual D, making sure you do not exceed velocity as stated by your states local code, or the International Mechanical Code...
I charge $200 on a retrofit or new install for this...and the reason is, its time consuming...you need about $300 just in manuals, and the online crap that is out there is normally wrong.
If you have never done one, but have the books, its almost guaranteed that your first 10 to 15 will be wrong....we go to class on it yearly...its changing that much.
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this is Turtle.
1) You was speaking of finding baffles , dampers, and other item in the ducts that is stopping the air. I don't need to see the outside or inside of the duct to know that it is there. I have equipment and tools that will tell me it is there along with the Maunul D data. I don't have to see something to know it is there. this is the reason we get the so called big bucks to do this type of work.
2) A system of ducts can be too big and cause the same problem like too small. A lot of people will just live with these problems for thinking it is too hard to or costly to correct problem like this. I have corrected systems like this by just installing a push baffle in it to change the air flow and not change the duct system at all. It can be little as a $4.00 baffle to a complete rework of the ducting system. It is most of the time be just a few minor changes to fix them.
3) If you hear roar , whisles, and little or no air out other vents sound like a OVER sizing problem to me or the ducts are too big and have to be restricted. Now i can't see it from here but this is what i think. Now if it is over sizing problem. I can fix them for about $150.00 including all equipment and labor. I have fix one for my friend with 2 bath towls and a manual D data. I would restrict air till my flow meter said the air flow was right out each of the registers.
TURTLE
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you're in Louisiana, from your server address), perhaps you can recommend someone up here ?

Give me the link (by email if you prefer) to download "Manual D". As to whether it's 'over my head' or not, is immaterial, as you have no knowledge of my background. In fact I worked, 10 years ago, at the University of Toronto, Dept. of Physics, Atmospheric Physics Group on mathematical modeling of closed-loop wind tunnel systems (wind tunnels that simulated a falling air particle, and the growth of ice crystals) and may know a lot more than what you presume.
Just because the data is fed into a computer, doesn't mean its impossible to understand (not to belittle your knowledge and training).
Regards, Alan
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