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Cogito Ergo Sum
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HVAC question. Any way to baffle a duct?
Our downstairs bedroom always seems to get more hot or cold air than any other room. So in the summer you get frozen out, burned out in the winter. Never been an issue since it was the guest room and rarely used, now Thuy's dad is living there, so it's becoming one. It has one 10" square vent that I have closed pretty much all the way, but the air is still whistling through. This room is the last one the duct, and I have all the other vents wide open. There is also a return duct in that room. It appears to just run upstairs to a grate near the return for the unit.
Anything I can put in that vent to baffle the air? Would like the cut down on air volume and speed, which should take care of the noise. The duct is between two floors, so no access to ductwork. |
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03-01-2016, 07:26 AM
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 HD sells these. There are fancier versions with two flaps.
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03-01-2016, 07:37 AM
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Wait. I didn't see this. So you don't have access to the duct? Duct tape the back of the vent? Stuff a tee shirt in the pipe behind it?
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03-01-2016, 07:40 AM
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Cogito Ergo Sum
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I've thought about covering 1/2 or 3/4 of the vent. But wouldn't that just increase pressure in the cent and make the noise worse?
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03-01-2016, 07:44 AM
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Banned
Join Date: Jan 2005
Location: cutler bay
Posts: 15,136
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would cutting up a a/c filter and stuffing it in the vent help with both the noise and flow volume ?
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03-01-2016, 08:12 AM
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Registered
Join Date: Mar 2004
Location: Los Angeles
Posts: 17,455
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Must find the main split on duct work and install a damper to force air to run to other side. Its should be up in the attic. Block out half the vent and see what happens.
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03-01-2016, 08:28 AM
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Cogito Ergo Sum
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Covered half with tape and opened up a bit more to help with the noise. We'll see how this works.
 Jeff that damper would work, but afaik there is only one duct that comes down stairs, I'd hate to dampen it, our living room would be unusable in the summer... |
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03-01-2016, 10:00 AM
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Join Date: Mar 2004
Location: Los Angeles
Posts: 17,455
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Sorry Sid, my dumb ass didn't read your post carefully. The return air is in that room? If so, then all the cold or hot throughout the whole is going there because that's where its sucking all the air back into the system. Since, its the last register or outlet on the line, there's really no reason its blowing stronger then others unless the others has bends in the line leading to it. How big is that duct behind that grill? You might be able to sneak in there and install a damper. It should fit pretty tight but it has to be sheet metal screwed to the metal round duct. Ideally, it should be install in the attic or upstream somewhere to prevent air velocity associated with noise. If you decided that you feeling crawling, find out the size of the flex duct (should be since its a newer house) and cut open and install damper and tape the heck out of it. This will force the air to the other outlets upstream.
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03-01-2016, 01:06 PM
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least common denominator
Join Date: Aug 2001
Location: San Pedro,CA
Posts: 22,506
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Any chance you can trace the duct back to the heater? Much more efficient to damper the duct where it leaves the plenum and you won't get all the whistling at the grill.
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Gary Fisher 29er 2019 Kia Stinger 2.0t gone  1995 Miata Sold 1984 944 Sold I am not lost for I know where I am, however where I am is lost. - Winnie the poo. |
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03-01-2016, 03:30 PM
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Takin' hard left turns
Join Date: Dec 2004
Location: So Cal
Posts: 1,412
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Put the duct in a round room and tell him to pee in the corner!
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03-01-2016, 03:53 PM
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Retired Member
Join Date: Sep 2005
Location: Guelph Ontario
Posts: 2,533
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If you can access the main supply duct there may be a damper on the run to the bedroom. If not what you did should work.
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80 911 SC sold 17 Tahoe 07 Z06 Corvette 
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03-01-2016, 05:47 PM
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Pull the grille off, there will be a box behind it with a round collar...let me know the dia. and I'll send you a damper.
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Jim 76 911s 3.6l Track Car 05 Ferrari F-430 "If its worth doing...it's worth doing to excess" |
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03-01-2016, 07:02 PM
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Student of the obvious
Join Date: May 2000
Location: Phoenix
Posts: 7,714
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We have the opposite problem. Airflow in our master bedroom isn't sufficient. It's always too warm in the summer compared to the rest of the house. I've traced the ductwork and it's not crimped... just doesn't seem to get enough airflow to cool the room. Do we need to turn down all the other vents just to cool the one room?
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Lee |
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03-01-2016, 07:29 PM
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How about focusing more on dampening/blocking the return. Wouldn't that moderate the temp better?
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David 1972 911T/S MFI Survivor |
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03-01-2016, 08:37 PM
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Banned
Join Date: Jan 2005
Location: cutler bay
Posts: 15,136
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Quote:
that would move more air when the fan is on |
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03-02-2016, 05:06 AM
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UnRegistered User
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That is called air balancing. You could have one take off that has a poor location. For example too many other take offs in the area or by a transition in the ductwork. Try reducing flow gradually to some of the other diffusers or registers and see if the volume picks up to the problem zone. You might be able to speed up the supply fan and then choke the flow to some of the other takeoffs. It really is tough to say without seeing the system. Is this particular room at the beginning or the end of the run? To the original poster, I have seen in one case where someone stuffed the duct with course stainless steel wool to reduce flow and noise when the balancing damper was not accessible. Problem was that after a period of time it loads up with dust as it acts as a filter. It actually did work quite well though....
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Bill K. "I started out with nothin and I still got most of it left...." 83 911 SC Guards Red (now gone) And I sold a bunch of parts I hadn't installed yet. |
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03-02-2016, 05:18 AM
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Registered
Join Date: Apr 2005
Location: outta here
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Quote:
JR |
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03-02-2016, 05:49 AM
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non-whiner
Join Date: Aug 2012
Location: Slightly right of center
Posts: 5,235
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If the return is in this room, that is your problem. It in effect pulls air into the room. To fix this you need a two step solution. Add a second return to another room and install a thermostatically controlled damper (the closer to the hvac unit the better) to the supply side. This is really your best solution and will give him complete control of the temperature in his room.
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"Too much is just enough." |
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03-02-2016, 07:19 AM
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Join Date: Apr 2005
Location: outta here
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If the return in the room is not ducted to the plenum for the HVAC unit, but just returns air to the general area near the actual return duct, then you can probably just block that return. Air will still exit the room, assuming the door has the proper clearance on the bottom and will make it's way through the house back to the unit. That might cut down the volume enough to make it more habitable in the room. If not, smaller grill.... or anything that reduces the airflow to that room.
You could also fix it by opening a window in the room, some of the time... JR |
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03-02-2016, 07:32 AM
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Cogito Ergo Sum
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03-02-2016, 08:41 AM
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1986 Porsche 944 2.5l
2005 Ferrari F-430
Payne-Killer
1976 Porsche 911
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