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We moved into a new house last year, the central A/C works great for all the rooms (even for closet) but we have a problem in just one room. There is almost no air flow coming from that room's air duct.

The room is the northeast corner of the house, so it does not get almost any sunlight (Just east wall in the morning and there is no window on that wall) but still the room 3-4 degrees hotter than the rest of the house. (We also had the same problem during winter, all around the house was warm, but not that room)

I placed paper strips to each duct outlet to see the air flow, all the papers move except that room. That way I know that there is no air flow in that room.

I closed some other air ducts to increase airspeed, but so far didn't help.

What should I do to find & fix this problem?

  • Is there a return in the room? Are there any dampers on the ducts? Have you taken off the register, and taken a look inside (maybe the previous owner stashed some cash in there)? – Tester101 Aug 31 '14 at 14:56
  • Yes, there is a return in the room (I did not notice before). How it would effect the performance of the register? Just take of the register, no visible damage or stashed cash. I will go into attic and try to check the rest of the duct. – dvdmn Aug 31 '14 at 15:04
  • If air can't come out, air won't go in. If the room doesn't have a return, conditioned air into the room can be restricted. – Tester101 Aug 31 '14 at 15:16
  • Any chance the room in question was an addition? – Tester101 Aug 31 '14 at 15:21
  • If you have access to the ducts, look for loose or disconnected seams, and holes or damage to the ducts. If you don't see anything obvious, you might want to either take the ducts apart and inspect them, or have a professional clean and inspect them. – Tester101 Aug 31 '14 at 15:25
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Disconnected duct-work, a closed shut-off louver (somewhere in the duct-work, not at the register), or it's the longest and hardest-to-run stretch, therefore possibly undersized to fit in the space or a poor job done connecting it, are all likely culprits. Contract someone who has troubleshooting experience and an inspection camera. Standard duct cleaning service companies aren't likely to have either. Re-balancing the system will not solve the problem as you have tried that already (unless it is a hidden closed louver).

If I had to guess (if it's not just broken duct-work), it's the longest, hardest-to, smallest diameter run in the house, running in horribly mangled (kinked) 6" flexible. Solution, replace with ridged.

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