Keeping round duct together (HVAC)

[Stephen Tashiro]

Some videos that show how to snap together a section of round metal duct also show that it can be taken apart just by dropping it on the floor. (e.g.https://www.youtube.com/watch?v=seGVzTHFFgU ) After a piece of round duct is assembled, do people ever use screws to keep it together? Is sealant applied along the seam sufficient to do that? Do miscellaneous things like duct hangers and joints with other pieces of duct keep the seam from un-snapping?

[Maurice Mcmurry]

I try to avoid putting a screw in the lock. A screw hole in the lock creates a problem in the future. Occasionally a joint is problematic and I will screw the lock together. Quality control of mass produced stove pipe varies. If the lock was formed properly the joint should stay together until it is forced out of round.

[Jim Becker]

When I was using snaplock duct in the old shop, I did use screws or pop rivets, but only at high stress areas, such as near drops, etc. That presented the minimal amount of protrusions into the air stream while providing physical support where it was needed the most. Otherwise, I used foil tape which not only seals extremely well, but also has surprising strength. It was also easy to cut should something need to be rearranged.

[Jay Bryant]

I find that foil tape on the seams is sufficient, and it reduces suction loss. Getting the seams to come apart is more difficult for me. The throw it on the floor method is new to me, something I usually strive not to do. I do use rivets to join elbows and other components, especially on vertical sections.

[George Yetka]

Snaplock isnt ideal for DC its meant as a pressure duct. Air supply/exhaust/ or at worse return side of fan. Theres no reason you cant add a connector. Hose clamps can be used to keep it round which will in turn help to keep the lock done

[Maurice Mcmurry]

I agree with George about Snaplock not being ideal. It works on my 2 hp DC. In the shop with a 5 hp D.C. a section of light gauge round snap lock collapsed. In the really nice shop we had heavy gauge spiral pipe.

[Ole Anderson]

I agree with George about Snaplock not being ideal. It works on my 2 hp DC. In the shop with a 5 hp D.C. a section of light gauge round snap lock collapsed. In the really nice shop we had heavy gauge spiral pipe.

I doubt 26 ga snaplock would collapse, yours was most likely the less expensive 30 ga stuff. My setup includes up to 7" 26 ga snaplock, seams sealed with foil tape. Never a problem in a dozen years with my Oneida DC. Huge difference between 26 and 30 ga. Nothing wrong with using snaplock for dust collection.

[Stephen Tashiro]

26 gauge snap-lock (sometimes called stove pipe) is ok for dust collection purposes

My post was moved from Off Topic into the Workshops section, so it's natural to assume the goal is dust collection, but I'm actually assembling duct for heating and cooling.

[Bill Dufour]

I used a hunk of 2x lumber supported at each end on a sawhorse or block of wood larger then the duct diameter. Thread the 2x down the duct then place the assembly on each end. Then quick taps with a rubber mallet on the seam as needed.
I tried doing it flat on the floor and swinging the hammer inside the duct. not easy to do.
Bill D.
Bill D

[Jim Becker]

My post was moved from Off Topic into the Workshops section, so it's natural to assume the goal is dust collection, but I'm actually assembling duct for heating and cooling.

Well, ok now. There was no indication of that in the OP. I'll move it back.

My advise stands, however...foil tape unless there's a joint that's going to get stressed a lot for some reason.

[Brian Elfert]

I had a forced air HVAC system installed in my house after I bought it. The round duct is all screwed at the joints and a brush on sealant was used to seal the joints. (The house had electric baseboard heat when I bought it and the electric bill was extremely high.)

[Bill George]

I had a forced air HVAC system installed in my house after I bought it. The round duct is all screwed at the joints and a brush on sealant was used to seal the joints. (The house had electric baseboard heat when I bought it and the electric bill was extremely high.)

Three screws at each joint and duct seal brush on also. I forget the real name we called it Hard Cast sealant.

[Tom Bender]

Snap lock duct should be fine if it is not put under full suction. Screws and rivets may catch tangly stuff and can be a real pain if the duct needs to be cleaned. Tape around the joints should hold fine. The seams are pretty tight but tape wouldn't hurt.

[Jim Becker]

Snap lock duct should be fine if it is not put under full suction. Screws and rivets may catch tangly stuff and can be a real pain if the duct needs to be cleaned. Tape around the joints should hold fine. The seams are pretty tight but tape wouldn't hurt.

This is HVAC, not DC. Low positive pressure.