Air vent\duct not enough air is coming


My tenant recently complained about one of the bedroom upstairs being too hot. When I checked the vents in the floor (there are 2 vents) in this bedroom, one of them has more air blowing than the other one. I also checked all the rooms, and there is more air blowing on all of them. Except this one vent in the bedroom does not have enough air blowing. For this vent that has a problem, I opened the vent and checked if there is anything stuck which I did not see and everything seems to ok as far as I know. Is there something I can do to fix this problem?
Thank you very much for your help.
Annur
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Are you sure its not the return vent you are troublshooting? Put a piece of pape or tissue up to this vent. If it sucks air, the that is the return. As far as being too hot, why can't you partially close the vent that is blowing out air.
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Sometimes there are dampers at the air handler that can be used to adjust the airflow. Check there next. Usually they stick out where the flex duct attaches.
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Did it ever work right, maybe its a poor design, as someone else mentioned check for vents at the furnace, I have them to balance my system.
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Why would any HVAC contractor go through the trouble and expense to install TWO vents in to the same room? Is the room very large? Something doesn’t make sense.
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Geez, many if not most rooms have more than one HVAC registers.
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Very possible there is a damper in the cellar that is partly closed. Here is a picture of the ones typical near me.
http://www.hvacsolutionsdirect.com/images/P/Damper%20w%20Collar%20AR-1.JPG
If the handle is in line with the tube, it's open. Across, is closed. Two adults with walkie talkies can trouble shoot that pretty quick. Sometimes if the adult upstairs bangs on the duct with a metal screw driver, the one downstairs can tell which duct it is. Yelling into the duct from above can also help pinpoint.
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Worst case, if you can't find a control damper somewhere in the ductwork, replace the existing grill with a new one that has a damper on it so you can open or close the grill.
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Trace out the path from that register back to the main duct or furnace. First, make sure that nothing has come disconnected. It's common for taped joints to come apart and either leak badly or fall apart completely.
As others have pointed out, it's possible you will find a flap in a duct that controls the amount of air going to that register. If so, if it's not fully open you can adjust it.
It's also possible that this particular run is farthest away from the blower, is long, more turns, etc. For that, there are a couple of possible fixes. One is the type of add-on blower that just sits on top of the register and gets plugged into a wall outlet. It senses when the system is on and turns itself on, pulling air out of the register.
The other is an auxilliary blower that gets inserted into the duct section going to that register or perhaps a couple of registers on the same section that need more volume. The blower is powered off of the furnace blower or with a sail type switch in the duct. I installed one of those and it made a significant difference in airflow in the upstairs bedrooms farthest from the furnace.
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On May 19, 9:15 am, snipped-for-privacy@optonline.net wrote:

I would use the auxillary blower as a last resort. I have two vents with very long runs. It made it difficult to keep our bonus room comfortable. I think it's a common problem with bonus rooms since they are often far from the air handler. I replaced the 6" flex with 8" flex and that solved the problem.
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My tenant recently complained about one of the bedroom upstairs being too hot. When I checked the vents in the floor (there are 2 vents) in this bedroom, one of them has more air blowing than the other one. I also checked all the rooms, and there is more air blowing on all of them. Except this one vent in the bedroom does not have enough air blowing. For this vent that has a problem, I opened the vent and checked if there is anything stuck which I did not see and everything seems to ok as far as I know. Is there something I can do to fix this problem?
Thank you very much for your help.
Annur
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My tenant recently complained about one of the bedroom upstairs being too hot. When I checked the vents in the floor (there are 2 vents) in this bedroom, one of them has more air blowing than the other one. I also checked all the rooms, and there is more air blowing on all of them. Except this one vent in the bedroom does not have enough air blowing. For this vent that has a problem, I opened the vent and checked if there is anything stuck which I did not see and everything seems to ok as far as I know. Is there something I can do to fix this problem?
Thank you very much for your help.
Annur
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annur wrote:

Close the vents that do work partway, so more of the air will go to the slow one. Look for controls on the vents closer to the A/C, such as in the basement ceiling - there could be one for the slow vent partially closed.
They do make booster fans that can be inserted into ducts.
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Is the tenant complaining about not enough air conditioning, or too much heat?
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