HVAC dust collection fittings: what happens if you did keep everything reversed?

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Forum topic by Holbs posted 11-23-2016 01:31 AM 636 views 0 times favorited 5 replies Add to Favorites Watch
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2003 posts in 2227 days

11-23-2016 01:31 AM

As most know, HVAC metal ducts & fittings are designed for outward airflow, not inward. Hence, the crimped ends in a wood shop would face toward the machine, not the dust collector, when bought at a store. We have to cut out the factory crimp ends and hand crimped other ends. I am in the midst of yet again, reconfiguring my 6” HVAC ducts. While at Home Depot, I fitted a couple couplers and a 45 degree fitting out of curiosity… and the factory crimped ends did not seem too drastic from what I know of dust collector ductings. It got me thinking… has anyone kept the factory crimps facing toward the machines? Any science behind the loss of CFM or wind pattern disruption if the factory crimp is facing towards machines? I would imagine…after a couple runs, dust & debris would clog up the surrounding crimp ends anyways to add additional sealing aspects in regards to airflow.


-- The Carpenter Bee is derived from the Ancient Greek word wood-cutter "xylokopos/ξυλοκὀπος"

5 replies so far

View Fred Hargis's profile

Fred Hargis

5171 posts in 2691 days

#1 posted 11-23-2016 11:55 AM

In my last system I had one or 2 facing backwards and it didn’t seem to matter, but my joints are all sealed at assembly. My guess (and it is a guess) is that if you had them all facing backwards it would have some impact, but how much would depend on so many factors it would be hard to make a general statement.

-- Our village hasn't lost it's idiot, he was elected to congress.

View CharleyL's profile


223 posts in 3562 days

#2 posted 11-23-2016 03:51 PM

Orienting them correctly for the direction of air flow will reduce the static pressure, since the joints will create less turbulence when oriented properly. How much of this mis-orientations will affect your system will depend on the system’s design and duct size, but striving for the lowest static pressure in the system design and installation should be the goal. In a dust collection system, all joints need to be sealed very well and as smooth as possible inside.


View MrRon's profile


5190 posts in 3441 days

#3 posted 11-23-2016 06:03 PM

You can have a problem if you process materials that create long strands rather than dust/chips. An example would be drilling soft metals like aluminum on a drill press. The long spirals can catch on the crimped ends of the duct and cause a blockage.

View Jim Finn's profile

Jim Finn

2686 posts in 3120 days

#4 posted 11-23-2016 10:58 PM

Where possible, you can use a, brush on, sealer on the inside of the joints. That should help.

-- No PHD just a DD214 Website>

View Holbs's profile


2003 posts in 2227 days

#5 posted 11-24-2016 01:39 AM

I could seen planer or jointer shavings causing long strand air flow disruptions along jagged HVAC internal crimps. I could see that after enough time passed, those strands would build up enough to disrupt air flow. Yea…forgot about those long strands. Dang it…

-- The Carpenter Bee is derived from the Ancient Greek word wood-cutter "xylokopos/ξυλοκὀπος"

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