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Forced air heating system is making popping sounds?!

One of the bedrooms has a popping sound coming from the heating vent; rather like the sound a pebble makes hitting your windshield. It is only that one vent, so presumably it is related to duct going to that bedroom.
I took the grill off and found a 90* register duct boot (yes, I looked it up) with a oval duct going into it. The two were not fastened together and the duct was puckered on the sides. That seemed like a possible source of the noise.
The junction between the two was a couple inches below the level of the floor, so it was difficult to do anything with; but I have a vise grip for welding with very long jaws. Because of the floor, there was no way to actually get to the junction, but I put a piece of wood inside the duct and clamped it to the baseboard with the vise grip. That secured the junction reasonable well.
The popping noise didn't go away completely, but it got much quieter and less frequent.

So, did I find the source of the noise, or was it just a coincidence?

If the source, the only way to fix it (I can't leave the vise grips there!) that I can see is to put a hole through the baseboard, the drywall, and the duct boot; and to bolt a piece of wood there so it serves the same purpose as the piece of wood now held by the vise grip.
This would be a good amount of work (and possibly damage) so I would like to know if it makes sense before I do it.
Any advice would be appreciated.

I am sorry if this is a confusing description, but it is a confusing situation.

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 22,964
    That joint -- or the immediate vicinity -- is likely the cause of you popping noise due to expansion and contraction as the temperature changes.

    You need to stabilise that connection (while making remarks about the workman who didn't). Can you get room inside to work with it? And is there plenty of overlap between the boot and the oval duct? If so, you could see about getting some high temperature sealant squeezed between the two, and then securing it with at least four and preferable six sheet metal screws of even pop rivets...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • HVACNUT
    HVACNUT Member Posts: 5,761
    Are you saying the boot opening is round but the duct is oval? 
    If there's access underneath, they make oval to round adapters. 
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,608
    edited December 2023
    Someone placed that sheetrock and baseboard over that incorrect attempt at connecting the boot to the duct. That said, someone can remove said baseboard, sheetrock and perhaps other building material in order to gain access to correct the poorly installed ductwork.

    After the connection is repaired, I bet you dollars to donuts that you can find a craftsman to put sheetrock and molding back in place to look line it was never touched. Just like the folks who did it the first time. Really they are out there.

    After all that work is done, you may even find some paint that is a close enough match to the color of the wall and baseboard to make it look like new!

    As far as your query on putting a piece of wood to do what the vice grip is doing, I would go a little further to see if you can do it just like all the other duct connections to boots are in the rest of the house. With a real connection with screws like the professionals do it. If you are going to do it, you may as well do it right!
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • Tollerheating
    Tollerheating Member Posts: 6
    I should have included a photo with my first post.
    The oval duct is about 3" wide. The junction is 9" down from the top, about 2" below the floor level. There is another floor below this.

    I expect someone could rip the wall and floor out and rebuild it properly, but I hate to think what that would cost.
    My temporary fix, with the clamp and the piece of wood, corrects 80% of the problem. If I can fasten the wood in place permanently and get rid of the clamp I would consider it good.
  • Tollerheating
    Tollerheating Member Posts: 6
    HVACNUT said:

    Are you saying the boot opening is round but the duct is oval? 
    If there's access underneath, they make oval to round adapters. 

    No, they are both oval; they simply are fastened together. There is no access below.
  • Tollerheating
    Tollerheating Member Posts: 6

    That joint -- or the immediate vicinity -- is likely the cause of you popping noise due to expansion and contraction as the temperature changes.

    You need to stabilise that connection (while making remarks about the workman who didn't). Can you get room inside to work with it? And is there plenty of overlap between the boot and the oval duct? If so, you could see about getting some high temperature sealant squeezed between the two, and then securing it with at least four and preferable six sheet metal screws of even pop rivets...

    I don't know how much overlap there is, given its location I can't really even see it.
    I have a right angle screwdriver and thought maybe I could get it in there, with since it is only 3" wide there is simply no room to work in.

    What is this high temperature sealant? I thought of trying to get some epoxy putty in, but if there is a product actually made for the purpose...
  • Jamie Hall
    Jamie Hall Member Posts: 22,964
    I was thinking of RTV silicone. I wonder if there is any lip of the boot below the opening you could fasten to.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,608
    edited December 2023
    OMG... this is too easy. You needed to show that picture earlier. Three drywall screws about 2" long is all you need. . Try to get low enough on the baseboard to catch both the boot and the duct inside the boot for a stronger connection to the sheet metal. You can adjust how far in the metal the screws go in order to reduce or eliminate the noise. The goal is to get the proper tension on the metal and also countersink the screw heads.
    Then just paint the ends after you do the fix.


    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    CLamb
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,608
    Now I can add my comment that first came to mind.


    Forced air heating system is making popping sounds?!

    Is that in the kids room? Look for the Orville Redenbacher package inside the ductwork

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    CLamb
  • Tollerheating
    Tollerheating Member Posts: 6

    OMG... this is too easy. You needed to show that picture earlier. Three drywall screws about 2" long is all you need. . Try to get low enough on the baseboard to catch both the boot and the duct inside the boot for a stronger connection to the sheet metal. You can adjust how far in the metal the screws go in order to reduce or eliminate the noise. The goal is to get the proper tension on the metal and also countersink the screw heads.
    Then just paint the ends after you do the fix.


    I'd love to do that, but as I said, the junction is about 2" below the floor level. I can capture the boot easily enough, but the bottom piece is out of reach. That's why I mentioned putting a piece of wood inside the boot and bolting that to the boot so it would apply pressure down below on the duct.

    But, I have a new idea. Hinge two pieces of wood together, put them down in the junction, straighten them out so they will apply pressure to both sides of the junction and sliding a lock to keep them in place. It will be tough to do so far down, but I think i can do it.

    Also, I might be able to put screws in the narrow sides of the oval where I will have more room to work. It might help. Again, doing it that far down won't be easy.
  • neilc
    neilc Member Posts: 2,671
    edited December 2023
    Nvrmd,

    , , , the bottom piece is out of reach. , , ,

    can you reach down and touch the junction?
    reach down with finger full daubs of a good silicone, or urathane caulk, or duct pookie, and daub it into the joint, all the way around,
    wear gloves,
    just try to get stuff into that seam, and stabalize it,
    you might even try to get a small tool into the seam to open it a bit to allow better application penetration,
    then pull the tool and the caulk may spread deeper thru the joint,
    known to beat dead horses
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,608
    edited December 2023
    Have you tried to pull up on the Oval Duct? you can use duct tape to offer a grip to lift. Really, Duct tape can be used for Duct Work. (see file below for larger illustration)

    I would get some really strong sticky stuff like this: https://www.supplyhouse.com/Venture-Tape-1580P-3-Duct-Joint-Sealing-Mastik-Tape-Printed-UL-181B-FX-Listed-3-x-100?_br_psugg_q=mastic+tape. It ain't cheep, but it won't let go. You can leave the backing on the part of the tape you don't want to stick until you have pulled the duct up to meet the boot.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    CLamb
  • Tollerheating
    Tollerheating Member Posts: 6
    I tried both a right angle drill and a right angle/extension on a impulse driver to get some screws in. While they are just long enough, I don't have enough control over them to actually get a screw in. But... I did find that there is one screw already there at each end. Presumably after 18 years they have loosened enough to be ineffective. (but they would prevent me from pulling the oval duct up any higher)

    I got rid of 80% of the problem by jamming a pair of 3.25" wood blocks in the junction, which is about 3" wide. Now it only makes a popping noise occasionally, but it is still rather loud.

    I am thinking of improving it by either:
    1) replacing the 3.25" blocks with 3.5" blocks. It will obviously be tighter but I am afraid of actually breaking something.
    2) Following someone's suggestion and putting caulk in the pocket between the boot and the oval duct. It will be messy. both because i can't actually see what I am doing, and because much of will squeeze out when I put the 3.25" block back, as they will flatten the pocket. Would having caulk on the inside of the duct make any difference? I don't suppose it would burn, but the heat might make it smell bad.

    Do either of these seem reasonable?