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Every time the heat turns on (rented house), we are getting choked with too much dry hot air in our small room. When I try to close the supply vent it produces a really loud whistling noise. I either lose sleep because of the noise, or because of the dry heat blast. When I close the vent enough to have heat levels acceptable, it is like trying to sleep in a whistling wind tunnel.

I believe there is too much air coming out of all the vents, frankly, but I am not the owner of the house, so would like a simple DIY solution involving filters, or a new vent, or something else I could install.

I could just cover the vent with foil, effectively disabling that vent (I cannot turn off the heat in the entire house, as other rooms need it). Is that safe, and more importantly, is there a better solution?

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    Rather that q questionable fix with foil, they do sell diverters and covers that are magnetic for redirecting and closing vents respectively. Also, make sure that all the other vents in the house are fully opened.
    – JPhi1618
    Nov 24, 2015 at 14:55
  • Yes, all other vents are open: problem is there is dual hvac in the house, and top floor has only four vents total. Is there a "volume control knob" on the heating system I can request the landlord to have adjusted? (Note magnetic cover won't do it: air will whistle and blast through the little slot that is for handle used to adjust vent!--hole in drywall was not cut properly so vent is not properly sealed)
    – neuronet
    Nov 24, 2015 at 14:57
  • Dual as in two completely separate units, or is there one unit with a set of diverters that "turn on" upstairs and downstairs separately?
    – JPhi1618
    Nov 24, 2015 at 14:59
  • There are two separate units.
    – neuronet
    Oct 16, 2017 at 13:32

5 Answers 5

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here is a really simply DIY fix. assuming the register is something like a standard 4 x 10. go and get yourself 2 foam sponges, cut to width and place into the floor register below the grate. by trimming them to length, you can tune the amount of air flowing past them, effectively choking the pipe off or reducing the flow to where your room is comfortable. the foam should act as an acoustical damper for the whistling you were hearing, and even though the air that gets through will be going faster, an thus might be louder, you can experiment with different shapes cut into the edges of the opening to introduce turbulence to slow down the flow further. entirely theoretical, but very similar to something I once worked on.

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  • Prettty much am doing something like this, will update if it works.
    – neuronet
    Nov 26, 2015 at 14:27
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    Update: I did this: I actually used about 6 inches of acoustically insulating foam that I cut to the shape of the duct-work. I got this at Guitar center. I also shoved a couple of towels up in there. For good measure. It worked like a charm. And never caught fire. :) It also never got warm in that room again. :O
    – neuronet
    Oct 16, 2017 at 13:35
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Forget any suggestions for restricting the airflow at the grille. The proper way to control airflow in ductwork is with an in-line damper which is placed as far up line as possible in the trunk or branch without affecting any duct drops that don't need the airflow restricted. The reason for this is efficiency and noise. I'm writing this from my phone, but I'm going to attempt to include photos.Damper Example of how you might install

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  • Great helpful stuff. I am renting this house, so that isn't something I could do, but I could suggest it to the landlord. :)
    – neuronet
    Nov 24, 2015 at 17:06
  • Note this is probably what I would accept if it were my house, and wanted to do it right, but the accepted answer is what I ended up doing in my rental, that I could reverse before we moved out. Thanks for this thorough explanation though.
    – neuronet
    Oct 16, 2017 at 13:34
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I'm not an A/C expert, so someone might have a more correct solution, but I have dealt with this before.

If the problem goes away when the upstairs and downstairs are on at the same time, then there is only one unit with a set of diverters (dampers) that close off one section of the house. In that case, you (or someone...) might be able to adjust the downstairs damper to never fully close, or to somehow always pass some amount of air, reducing the pressure in the upstairs ducts.

If you always have a problem upstairs there are probably two units, and it sounds like the one for the upstairs area is over-sized for the number of vents. This doesn't have a quick fix.

Some blowers can be rewired to reduce their speed, but the A/C coil and heating elements require a certain air speed to work properly, so that might not even be an option.

Closing off one vent in a system that already has too much pressure runs the risk of tearing open a seam in the ducting. That's bad because the problem might seem fixed, but you're dumping a lot of energy (money) into the attic.

Increasing the size or quantity of the vents is an option, but again, not an easy one.

Finally, one "solution" that I used in a similar situation - remove the vent completely in other rooms. It will increase the air flow in those rooms and should reduce the pressure enough in the problem room to stop the whistling.

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  • Forget any suggestions for restricting the airflow at the grille. The proper way to control airflow in ductwork is with an in-line damper which is placed as far up line as possible in the trunk or branch without affecting any duct drops that don't need the airflow restricted. The reason for this is efficiency and noise. I'm writing this from my phone, but I'm going to attempt to include photos.
    – bigbull15
    Nov 24, 2015 at 16:51
  • I like the idea of removing vents in other rooms, but landlord might not like it.
    – neuronet
    Nov 24, 2015 at 17:10
  • Well, removing a vent in the ceiling is normally two screws, and very easy to replace. It won't hurt anything and is something you can do with no special tools or even getting into the attic.
    – JPhi1618
    Nov 24, 2015 at 17:37
  • Yes, she is very weird. I should try it, if she complains I can easily replace. Good point.
    – neuronet
    Nov 24, 2015 at 17:41
  • I did remove vents in other rooms. It didn't solve problem unfortunately.
    – neuronet
    Oct 16, 2017 at 13:34
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Most furnaces have blower motors with multiple taps to adjust the speed.

Selecting a lower blower speed to reduce noise and increase comfort is usually no more complicated than changing the connection of a single wire, however anyone who does this must confirm that the supply air is not hotter than 130F after making this change.

This should be something the Landlord can handle.

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  • Blowers are typically set to the lowest speed, when in heat mode. Adjusting the speed could cause poor performance, and/or overheating of the unit. Blower speed is not some arbitrary setting, that should be blindly adjusted.
    – Tester101
    Nov 24, 2015 at 17:35
  • @Tester101 - Some are set to low, others are not. Please notice that I did mention the supply air temperature from the furnace is a limiting factor. Also, restricting airflow by other means such as blocking off registers or installing balancing dampers has exactly the same limitation, and those options hurt energy efficiency unless the net airflow is simply redirected and not restricted.
    – user39367
    Nov 25, 2015 at 0:40
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I had one vent that was making whining noise in a back bedroom . I bought $6 car door edge strip (has a U profile shape) and put it on the sealing edge of my vent and it stopped the noise. It was enough to stop the resonance and natural frequency of the vent grill.

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    Jul 20, 2019 at 11:10

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