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[HVAC] Noisy AC vent

I live in a two story 1986 townhouse in S FL with a 1 year old single AC unit (4 ton) We replaced the AHU with a variable speed fan Trane unit and it moves much more air than the previous one. We did so because the HVAC sales person said we might be able to resolve the low flow issue to the upstairs vent by increasing the available supply air volume. The AHU is located just below the first supply vent which has a 8" x 18" vent installed and provides the bulk of the air to the main floor. The air movement noise is so loud one cannot hear the television and you have to speak really loud to be heard. When I remove the vent the noise dissipates and so does distribution to the balance of the vents throughout the house.

I have looked around the web for a suitable solution but have seen anything that might fix this issue. We tried lowering the fan speed but that results in the upstairs area starving for cool air. I am wondering if there might be a way to balance the air flow from this vent to others in the house or to source a quieter vent.

I am open to any an all suggestions. Thx...

Msradell
Premium Member
join:2008-12-25
Louisville, KY

Msradell

Premium Member

Balancing airflow in an HVAC system is really an art and many times what you see is the end result when airflows are increased dramatically. What do you mean when you said you remove the vent? I'm assuming you mean you just remove the louvered piece on the end. This would probably quiet it down because that vent would no longer be providing any restriction to airflow.

Balancing needs to be done with in-line dampers instead of the dampers at the events themselves. In addition duct sizing plays an important part in distributing airflow correctly without the problems you are seeing. Getting it quieted down without losing the increased flows to other areas of your home is going to be nearly impossible without major changes to your ductwork.

nunya
LXI 483
MVM
join:2000-12-23
O Fallon, MO

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I have one of those. Drives me nuts.
I replaced the old grill with a "wide cut" grill. That helped a little. Not much though.

pende_tim
Premium Member
join:2004-01-04
Selbyville, DE

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As a temporary fix until you can get things properly balanced, try putting a piece of cardboard under the 8"x18" louver. You will have to play with the size a bit to get proper flow so the adjacent area is cool enough and the upstairs is also cool enough.

Open up the vent shutters all the way and start with a piece 4" x 18" under the louver and adjust from there.

However before you go that route, look at the duct work and see if there is a damper already installed in the branch. It may be under some insulation, assuming the ductwork is insulated.

How much did the salesman upsize your unit? An AC unit needs to be sized based on cooling load/heating load not airflow! An oversized system will result in high humidity and short compressor cycling. Both are energy wasters: the high humidity makes it feel warmer inside and you will want to decrease the indoor temperature. The short cycles prevent the unit from operating at an efficient SEER. The problem is compounded as systems nowadays are setup to run the fan after the thermostat is satisfied. This tends to evaporate the moisture left on the evaporator coils and put it back in your house. The more often the system starts and stops, the more this effect is noticeable. Ideally you want the system to be sized to run all the time. This way the moisture on the coils is never evaporated back into the room.

If airflow/hot&cold rooms is a problem, the system needs to be balanced.

Tex
Dave's not here
Premium Member
join:2012-10-20

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When you mentioned you have a 2-story townhouse with one system, I cringe. If your townhouse system is like most townhouse systems I've worked on, the duct work is virtually inaccessible and nothing can be done to balance the airflow. Is this 8" x 18" diffuser located in the sidewall where the indoor unit is located? I picture the indoor unit located in a small closet on a platform with the return air filter grill located under the access door to the air handling equipment.

Your statement about the HVAC sales person saying you might resolve the low airflow issue with a 4 ton air handler also has me cringing. You cannot move 4 tons of air through 3 tons of poorly designed duct work. Of course, I'm making assumptions, but you really didn't provide enough information about the system nor did you include any photos with your post as required by the forum rules.