More 30ga Duct Testing

[William C Rogers]

To start with I am not recommending the use of 30ga or the use of 26ga snap lock for ductwork. I am posting for information only. I posted a while back some testing I did with my 3hp Jet dust collector using 30ga ductwork. My DC is a 3hp Jet 1900. Specs say 1900 CFM, 5629 FPM, 12.5 static pressure @ 8". In my first test I only used three 5' sections (partly because my shop was a mess and clear space was an issue). Before I installed the duct I wanted to expand the test using close to what my longest run would be. At the end of the run I included one 5' vertical section. See third picture. The end at the DC has a elbow. I measured the thickness of all the components. All were 30ga except the wyes were 28ga. Components under test were six 5' pipe, 3 elbows, and 1 wye. I used the aluminum Lee Valey 6" aluminum blast gates.

The first test I repeated assembling all straight pipe with the seam on top and results were similar, the straight pipe went oval. No permanent set occurred, came back close to original shape when gate was opened.
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I then rotated the seams side to top and retested. The pipe didn't collapse when the gate was closed, however you could see where it was on the verge.

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Now for the fun, I slammed the gate shut in this configuration. The straight pipe "bounced" oval back to round. No permanent set in the straight pipe, but the vertical pipe did take a set which surprised me.

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Finally I put the plywood rings on the first four sections (that was all I had at the time and forgot to take picture). Repeated slamming the gate shut and there was no collapse.

My conclusions: I can get by with 30ga pipe using the plywood rings. Rotating the seams does help resisting pipe collapse. I will put one, maybe two plywood rings on each section of straight pipe and rotate the seams 90 degrees top to side. None of the elbows or wye showed any sign of collapsing. If I had a "do over" I would buy 26ga pipe, but use the 30ga fittings. I am using 6" pipe, so different pipe sizes and DC's will have different results. I will save some money using 30ga, but will involve more installation time.

[Ole Anderson]

Thanks, always nice to see folks go to the effort of testing things like this. And it verifies why I recommend to never use 30 gauge duct. But I am glad you were able to make it work for you.

[William C Rogers]

Thanks, always nice to see folks go to the effort of testing things like this. And it verifies why I recommend to never use 30 gauge duct. But I am glad you were able to make it work for you.

Thanks Ole, there were so many saying 30ga is not a problem. It is a problem if you don't take extra steps when installing. I didn't save much in the pipe (if bought from a HVAC supplier). The savings is really in the fittings.

[Peter Aeschliman]

Yeah, while it may be a workable material (plywood rings, etc), clearly if one has the means, heavier gauge is a much better choice. Thanks again for the real-world testing. It benefits us more than you. I really enjoyed your other thread as well.