Just my luck ~

[Jooced]

Hi guys, here's yet another basement question for you :cool:

I'm currently finishing my basement and I've installed 4 new heat registers (individual 6" new runs) and I was planning on installing 2 returns in the central area of the basement. I got the first one installed and it worked great. It was a 14"x6" and I used flex duct. Then, I get to my last return last night and once it's completed I have a strange hum and a 'blowing into a Coke bottle' harmonic sound. I can only hear this sound when we're in the room directly above (unfortunately, it's the master bedroom). I can not hear anything odd when I'm downstairs at the area. Very hard to describe but experience in the field might let that ring a bell.

Here is what I did for that return. It's in a bed room and would run up between the 2x4 of a closet wall off of a 12x6 return register. At the top of this is the sofit so I took a sheet metal 12"x16" with a 6" starting collar. Then 11" away is the main air return duct. So, I cut a hole in the side of the duct for simplicity, placed another 6" starting collar and connected the two with a custom cut 11" long 6" round duct.

I guess I'm sort of fishing for anyone who's had this issue in the past or if I've done something completely dumb by trying to keep it simple. I appreciate anyone’s input and the posts that are made on this board everyday. I’ve read so much on here allowing me to get as far as I have.

Just my luck though, everything went perfect HVAC-wise until the last run. :rolleyes:

[Jay11J]

Humm. Odd one...

Can you feel the humming sound when you press onto the duct work?

Does it go away when you remove the return grill?

[Jooced]

Thanks for the reply.

There's no grill yet since until there's sheet rock there is no enclosure. I can't feel the humming but did try to close the open end of the 11" run with no luck.

I'm starting to think that it could be the type of collar I used. Since there is no longer air going through the run (it's closed off) I can only guess the noise is coming from inside the main return duct (why we hear it upstairs) as it passes the opening I made.

I'll have to stop by Home Depot tonight to get a new starter collar and see if that does the trick. If not maybe I'll change the 11" long 6" tube to flex. Shouldn't matter but.... :confused:

[Ed Imeduc]

Can you be short on cold air return??? When blower is on try and open blower door see if it pulls real hard to open if so you can need more returns

ED ;)

[Jooced]

That was my original thought as well but looking back - when I had only added one of the two returns it was perfect. Adding the second is what created the issue. Sort of the opposite.

[Jooced]

Just to update my situation, I'm pretty sure this is a one time oddity that you'll never see again.


I took everything I had put up down last night and capped off the 6" starter collar. The noise was still there. So I went upstairs to the master bedroom where the noise was the loudest and began to listen to the returns. As you walk into the room the door opens to the left and behind there is a return. The doorway to the master bath is just beyond that to the left as well. On the other side of the bathroom door (still on the left wall) is another return (about 5 feet away from the first). If I were to cover either of those returns the noise went away. Hmmmm......

So I head back downstairs and notice that those two returns are sharing the same joist space. My hole I made is right before that joist in the direction the air travels. Somehow, that new hole created just the right disruption in the airflow for those two returns to cause a weird type of harmonic hum. So, I closed off one of the registers in the bed room so I could get some sleep but I'm not sure where to go from here.

Anyone know of anything I could install or just place in there that I could disrupt the disrupted airflow? :eek: That makes no sense.... would I just be better replacing the area I cut out and finding another area to install the return? If so, how hard is it to replace the large square I cut into (it's in the middle of the run).

Thanks again!

[Jay11J]

There's a return in your bathroom??? :thumbdn:

Close that off.. see what happens.

[Jooced]

Actually no, there isn't one in there. It's a large bathroom - 3 different vents in the three sections (main sink/shower, separate toilet section, master closet). I'm guessing that's why there are two returns directly outside of the bathroom.