Excessive noise between units travelling through air returns

SheldonP

Hello, I am hoping to find a solution to this issue.

We have a property that we converted to two units, but they share the same furnace and ductwork. The tenants upstairs have mentioned how noise really travels freely through the two units to the point where you can essentially hear full conversations with the downstairs tenants. I have gone to confirm and they are not exaggerating. The noise seems to predominately travel through the air returns as they share the same locations (the air return downstairs is directly below the upstairs vent)

The upstairs has a total of four vents (one in each bedroom and one large one in the hallway), while the downstairs has two vents (one in the kitchen and one in the hallway). These locations are where the downstairs tenants spend most of their time while talking

My question is can the two vents downstairs be eliminated and then install one in the furnace room to pull air? we could install a door vent on the furnace room door, plus the two bedroom doors so air can be pulled from the unit.

My other question, is there any other solutions to dampen the noise travelling through the vents, without the obvious solution of tearing drywall out and separating the air return vents in some way.

I am open to any and all solutions or suggestions.

Thanks,

Sheldon

ChrisJ

A short run of properly sized flex duct would help with the noise, a lot.

By short, I mean 3-5 feet.

Another option could be lining the ductwork, which many people do not like because you're putting fiberglass inside the ductwork. Third option is installing a length of ductboard, similar to lining a duct except the entire duct is made from fiberglass.



That said......I sure wouldn't like sharing a forced air furnace with someone else. You're sharing smells, cooking, literally everything. But, that's just me.

Jamie Hall

I agree with @ChrisJ in general -- I'd not like to share a forced air system with anyone, and preventing sound travel in ductwork is difficult, to put it mildly. He suggested sound insulation inside the ducts (you'll need to look at supplies as well as returns, but may I suggest using quality acoustic tile for the purpose? It shouldn't shed either fiberglass or anything else -- and perhaps more important isn't likely to collect and trap dust. Now how you go about getting it in there... at the very least you could remove the registers and line the ductwork inside as far as you could reach with acoustic tile.

It would also help if the ductwork could be redone to have the supplies and returns from each apartment pass through double U bends, acoustic lined, before jointing, but that this likely to be impossible.

I can't really recommend eliminating the return vents in either apartment, as this will almost inevitably lead to significant balance problems in air flow and thus heating between the two units.

EBEBRATT-Ed

Insteasd of traditional duct liner they now use Armaflex (rubber) for lining ducts that would help but may not eliminate the issue.

I think you are going to have to relocate the returns, perhaps adding a few smaller ones will help. I have also put returns in a closet with a louvered door on it.

yellowdog

Two separate furnaces with separate ductwork will be your only solution. I don't think you will ever get enough "insulation" in the ducts to stop the sound from communicating from one space to the other.

Jamie Hall

You might try this stuff:

https://www.parts-express.com/Sonic-Barrier-1-Acoustic-Foam-w-PSA-18-x-24-260-525?quantity=1

does a remarkable. Warning: when the say aggressive adhesive, they mean it...

ChrisJ

Depending on your location minisplits may be the easiest and most practical solution.

HVACNUT

The returns probably aren't even ducted. Just panned bay spaces. It's like cutting open a portion of the wall and just leaving it that way. Then they slap a stamp grill on it and call it a return.

EdTheHeaterMan

Have you tried turning the radio volume higher?

Or this

ChrisJ

EdTheHeaterMan said:

Have you tried turning the radio volume higher?

Or this

The fact you just recommended a device that never works, and that no one in it can ever hear the other person but everyone outside of it can......


I just don't know anymore........ Next you'll be recommending The Closet of Silence.

SheldonP

Just want to thank everyone for their suggestions, they are helpful in finding a mitigating solution for the time being.

I agree sharing ventilation isn't ideal, and if I was the one who built the 4-plex I would have separated the heating systems, but that isn't the reality and we have to play the hand we are dealt. Hopefully down the road we can separate the systems and not have this issue at all.

Thanks again.

Sheldon