HVAC Noise in Listening Area

[Pretorious]

Getting a little annoyed this evening by the sound of the air vents in my home (alongside other appliances), I decided to grab the SPL meter and measure what it was. Using C-weighting at my listening spot the meter was reading 56db. I measured 3 other potential areas in the house for listening space, but it's an open floor plan with limited spots, and noise tends to carry no matter what. Those 3 other spots measured within 1db of my first measurement, with the living room area near a set of vents and refrigerator hitting almost 60db.

If I'm listening to anything with quiet passages in it, forget it, it's very difficult to hear without turning up the volume to be obscene in louder passages. Try listening to a Bruckner symphony like that, half the music you will be straining to hear.

Anything I can do to improve the listening experience and reduce the background noise level of the house? Or am I doomed?

 

[Doodski]

If they are floor vents cover them with blankets and books or one of those custom magnetic metal sheets encases in rubber to be silent.

 

[Old_School_Brad]

Can the airflow on these vents be adjusted? If so, I’d reduce the flow on the ones nearest to the listening position to lower the noise. If the space is connected to a larger area, ventilation and temperature should remain mostly unaffected.

More importantly, I’d check the airflow and fan speed settings in your HVAC controller -it might be set too high. In my opinion, 60 dB from vents seems excessive. The system's airflow is likely too high relative to the vent openings, causing air turbulence and noise.

 

[DWPress]

Good luck, I went through 5 ceiling fans and 3 heater fans before I could tame my room down to 37dB and I live deep in the forest with no neighbors.

 

[Pretorious]

Airflow can be adjusted on the vents but this doesn’t achieve much. The sound seems to be coming from the rest of the length of the vent in the walls, resonance or air turbulence.

If I remember correctly, I think the fan speed is high because we have 2000 square feet of open floor plan to cover and the AC and heating provided by the association is inadequate to the size of the units. It’s something we’ve struggled with since we moved in, where basically just the main room gets proper airflow, the basement too much (where my listening space is) and the upstairs almost nothing. The fan speed is I believe an attempt to compensate to try and get more airflow elsewhere into the home.

I wasn’t sure if I have just become more sensitive to background noise, but near 60db seemed high to me regardless.

 

[amirm]

Are you hearing air flow or the noise from the HVAC motor? If former, then if you can, put in much larger vents. And/or more of them. This is what I have in our dedicated theater:

I have four of them to further reduce velocity.

If it is motor noise, then you need to build a muffler for them (larger duct en route to the vent).

 

[Pretorious]

Good luck, I went through 5 ceiling fans and 3 heater fans before I could tame my room down to 37dB and I live deep in the forest with no neighbors.

It seems to be the plight of a modern home. Noise canceling headphones look to be a better and better solution.

Are you hearing air flow or the noise from the HVAC motor? If former, then if you can, put in much larger vents. And/or more of them. This is what I have in our dedicated theater:

I have four of them to further reduce velocity.

If it is motor noise, then you need to build a muffler for them (larger duct en route to the vent).

It’s definitely the sound of the airflow itself; the same noise can be heard in every other area of the house, to a greater or lesser degree based on the strength of the flow. I can look into this as a solution though, thanks!

 

[Old_School_Brad]

Yes, airspeed does generate noise. You can reduce it by increasing the size of the openings, which maintains the same airflow while lowering the speed, or by simply restricting the airflow. These systems are likely proportional pressure systems, meaning that if you restrict the flow from the basement vent, more air will be directed through the other vents in the house.

As an experiment, try completely blocking the basement vent. If this eliminates the noise, you should partially restrict the airflow instead to reduce the sound.

Additionally, the ducts might be resonating due to improper fastening or lack of insulation.

Regardless, you shouldn’t be experiencing 60 dB of HVAC noise anywhere in your home regardless of weighting.

 

[amirm]

As an experiment, try completely blocking the basement vent. If this eliminates the noise, you should partially restrict the airflow instead to reduce the sound.

I would worry about the health of HVAC system this way. The coils can freeze in AC mode.

 

[Old_School_Brad]

I would worry about the health of HVAC system this way. The coils can freeze in AC mode.

That’s unlikely. The evaporator and condenser unit are self-monitoring, and blocking one vent will slightly reduce the cooling (or heating) demand, causing the compressor to adjust to run at a lower load.

In any case, this is just an experiment to help identify the source of the noise.

 

[Pretorious]

Yes, airspeed does generate noise. You can reduce it by increasing the size of the openings, which maintains the same airflow while lowering the speed, or by simply restricting the airflow. These systems are likely proportional pressure systems, meaning that if you restrict the flow from the basement vent, more air will be directed through the other vents in the house.

As an experiment, try completely blocking the basement vent. If this eliminates the noise, you should partially restrict the airflow instead to reduce the sound.

Additionally, the ducts might be resonating due to improper fastening or lack of insulation.

Regardless, you shouldn’t be experiencing 60 dB of HVAC noise anywhere in your home regardless of weighting.

This is something we thought of years ago based on similar experience with our old home. Unfortunately, running the vents full open or full closed made no appreciable difference in the noise level nor airflow elsewhere. We thought it would at least allow more than a minuscule amount of air to reach the second floor, but it never does. At anytime of the year, with the main floor as the baseline (since the thermostat is located here), the basement can be up to a 10 degree difference, and the second floor can be 5-6 degrees different.

With it being an open floor plan townhome with a 20 foot vaulted ceiling, I think the whole building just becomes a resonant chamber. I'll try more of these suggestions and look into getting some professional help, if nothing else works.

 

[Alice of Old Vincennes]

Yes, airspeed does generate noise. You can reduce it by increasing the size of the openings, which maintains the same airflow while lowering the speed, or by simply restricting the airflow. These systems are likely proportional pressure systems, meaning that if you restrict the flow from the basement vent, more air will be directed through the other vents in the house.

As an experiment, try completely blocking the basement vent. If this eliminates the noise, you should partially restrict the airflow instead to reduce the sound.

Additionally, the ducts might be resonating due to improper fastening or lack of insulation.

Regardless, you shouldn’t be experiencing 60 dB of HVAC noise anywhere in your home regardless of weighting.

Restricting air flow is never good idea. What size is ductwork? Is ductwork accessible? You could replace with larger ducts. Are some of vents already closed? Do you have high velocity system? Carefully inspect ductwork. Modern installers often do not properly seal. Never, ever use duct tape to seal. Mastic is gold standard. Rarely used today because it is sloppy and takes time. Next door neighbor has mastic 100 years old still sealing. Regardless, something is wrong unless you have high velocity system. I renovate houses on the side. Usually need to reseal ductwork due to sloppy installation.

 

[amirm]

That’s unlikely. The evaporator and condenser unit are self-monitoring, and blocking one vent will slightly reduce the cooling (or heating) demand, causing the compressor to adjust to run at a lower load.

Go tell that to countless people who have frozen coils due to clogged filters. Or any HVAC technician.

 

[Old_School_Brad]

Go tell that to countless people who have frozen coils due to clogged filters. Or any HVAC technician.

You're misunderstanding what I wrote.

You're referring to completely blocking the entire flow through the unit, which was never suggested.

I'm talking about blocking just one of multiple outlets. This will cause the HVAC unit to reduce the frequency of both its ventilation motor and coolant compressor motor since the overall load will decrease.

 

[Old_School_Brad]

Restricting air flow is never good idea. What size is ductwork? Is ductwork accessible? You could replace with larger ducts. Are some of vents already closed? Do you have high velocity system? Carefully inspect ductwork. Modern installers often do not properly seal. Never, ever use duct tape to seal. Mastic is gold standard. Rarely used today because it is sloppy and takes time. Next door neighbor has mastic 100 years old still sealing. Regardless, something is wrong unless you have high velocity system. I renovate houses on the side. Usually need to reseal ductwork due to sloppy installation.

I'm not suggesting blocking the entire airflow—just a single outlet, which won't harm the system in any way.

Keep in mind, this is a central HVAC system with ducts running throughout the building. Restricting or blocking airflow to one or more rooms will simply reduce the HVAC unit's load.

My suspicion is that the system is poorly dimensioned overall, or as you suggested, improperly installed.

This is something we thought of years ago based on similar experience with our old home. Unfortunately, running the vents full open or full closed made no appreciable difference in the noise level nor airflow elsewhere. We thought it would at least allow more than a minuscule amount of air to reach the second floor, but it never does. At anytime of the year, with the main floor as the baseline (since the thermostat is located here), the basement can be up to a 10 degree difference, and the second floor can be 5-6 degrees different.

With it being an open floor plan townhome with a 20 foot vaulted ceiling, I think the whole building just becomes a resonant chamber. I'll try more of these suggestions and look into getting some professional help, if nothing else works.

Based on my experience, I believe one or more of these issues might apply to your system:

• It wasn’t properly sized for the house.
• The HVAC unit and ductwork were installed hastily or incorrectly.
• The system was rushed through commissioning, leading to incorrect pressure setpoints and incorrect and imbalanced duct flow.
• Or a combination of all the above.

Ventilation systems serving multiple rooms often require careful manual measurement with a Pitot tube to get everything properly balanced. It’s a delicate act of adjusting pressure, temperature, and airflow. If you have a bit of OCD, it can actually feel meditative -at least, that was my experience during training. I imagine doing it daily would be a different story.

My point is: call in someone with the right expertise to set the system up correctly.

 

[Alice of Old Vincennes]

You're misunderstanding what I wrote.

You're referring to completely blocking the entire flow through the unit, which was never suggested.

I'm talking about blocking just one of multiple outlets. This will cause the HVAC unit to reduce the frequency of both its ventilation motor and coolant compressor motor since the overall load will decrease.

Need to use dampers instead of closing vents. Something really wrong with system that loud

 

[amirm]

You're misunderstanding what I wrote.

You're referring to completely blocking the entire flow through the unit, which was never suggested.

I was not. And you continue to be wrong. Please don't dispense advice in which you have no expertise.

 

[Old_School_Brad]

I was not. And you continue to be wrong. Please don't dispense advice in which you have no expertise.

I'm not wrong -I have experience with this.

Blocking one of multiple outlets will not harm a central HVAC system.

If you have evidence that this causes harm to a fairly modern system, I’d be interested in seeing it. However, your comparison to blocked filters isn’t relevant here. A clogged filter can restrict airflow through the entire unit, potentially causing damage (like a freezing coil) if there’s no alarm to detect high differential pressure. That’s not the same as blocking a single outlet.

Spoiler: HVAC multi-room example

 

[Alice of Old Vincennes]

I'm not suggesting blocking the entire airflow—just a single outlet, which won't harm the system in any way.

Keep in mind, this is a central HVAC system with ducts running throughout the building. Restricting or blocking airflow to one or more rooms will simply reduce the HVAC unit's load.

My suspicion is that the system is poorly dimensioned overall, or as you suggested, improperly installed.



Based on my experience, I believe one or more of these issues might apply to your system:

• It wasn’t properly sized for the house.
• The HVAC unit and ductwork were installed hastily or incorrectly.
• The system was rushed through commissioning, leading to incorrect pressure setpoints and incorrect and imbalanced duct flow.
• Or a combination of all the above.

Ventilation systems serving multiple rooms often require careful manual measurement with a Pitot tube to get everything properly balanced. It’s a delicate act of adjusting pressure, temperature, and airflow. If you have a bit of OCD, it can actually feel meditative -at least, that was my experience during training. I imagine doing it daily would be a different story.

My point is: call in someone with the right expertise to set the system up correctly.

Difficult to find someone these days. For example, no one in my area uses nitrogen after brazing a/c lines in spite of manufacturer's installation instructions. I can tell house I'm renovating was installed properly. Rudd furnace and A/C are nearly 40 years old and work fine. I'll bet nitrogen injected to purge lines. Original ductwork proper. Ductwork added later was pathetic.

 

[Old_School_Brad]

Difficult to find someone these days. For example, no one in my area uses nitrogen after brazing a/c lines in spite of manufacturer's installation instructions. I can tell house I'm renovating was installed properly. Rudd furnace and A/C are nearly 40 years old and work fine. I'll bet nitrogen injected to purge lines. Original ductwork proper. Ductwork added later was pathetic.

This aligns with my experience as well -it seems to be the same everywhere. No one takes their time; everything has to be done quickly. Incomplete evacuation of refrigerant circuits, inadequate pressure testing, and poor insulation on piping inevitably lead to condensation issues down the line.