In-line duct fan recommendations for long diameter ducts (~8"+)

I will be moving my glowforge into a commercial space that has a serious (and intimidating!) roof venting capabilities. I wasn’t able to take measurements yet, but wanted to ask if anyone has connected their glowforge to a much larger diameter exhaust duct and has recommendations for beefy fans

  • The room has a duct that looks like the aluminum hose that comes with the glowforge, but it is probably about 8" in diameter and goes up to the roof.
  • I can also use a huge fan that’s maybe 1 foot across and apparently very loud. I would prefer not to use it if I can help it.
  • I was thinking about getting the 6" AC Infinity fan and using a lot of adapters to get the air moving. (Glowforge 4" to 6" in line fan, then 6" in line fan to ~8" hose to the outside). but it would be better to get the largest fan possible right?
  • also considering a carbon filter at the end of the line
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GO big with the fan. the 6 inch AC infinity is great. Most of the versions I have seen have a speed control that you can use to slow it down if there is too much flow. I use a 6 inch at full speed to go a total of 7 feel across and 5 fee up from forge to wall vent. I had the 4 inch before that but the 6 inch works better.

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There’s an upper limit here, both aerodynamically and pressure wise. If you get a fan that can pull massive vacuum, you could collapse your duct or damage the machine. The 6" ac infinity is tried and true, I would think it would be enough fan.

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awesome! Yes I was eyeing the 6 inch AC infinity that everyone raves about. my little vivosun 4" does ok for small jobs, but it is definitely not pulling as much air as the glowforge air filter

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ah I didn’t expect there to be an upper limit, but that does make sense about the vacuum pressure. I was just worried that the length of the entire run (possibly 5-10 feet?) being much longer than my usual set up (<1 foot)

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keep in mind, fans like the infinity are variable speed fans. so you could run an 8" fan not at full speed going into that 8" output hose. that might actually be quieter than the 6" at full speed. i’m not sure what the CFM is on the 8".

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good point! I went and dug around for some numbers below. Might be a handy reference for folks in the future. I wonder if anyone has tried to find the upper limit? I’m imaging at the higher end, it becomes difficult to open the lid to the machine

Glowforge default air assist/air filter
~200 CFM estimate

195 CFM (actual CFM is probably lower from my experience)

402 CFM

807 CFM
(I guess this makes sense because there’s a square relationship between diameter and area)

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so, FWIW, i’ve run my 6" infinity at full speed regularly for the past year, no issues. sometimes i wish i could pull a little more (it’s probably time for a cleaning). that 807CFM is a lot. we have a big bofa filter at my office for a large universal PLS6 (32x18x9 bed) and i think we’re running it at ~500CFM (my memory is 532, site says 500). granted, the filter has a huge surface area in comparison and two stages, and is coming through two 6" tubes. so it’s a lot bigger. but the actual CFM to clear a larger laser bed is still ~500cfm.

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My exhaust run is over 40 feet, is 4" standard metal vent pipe, and I run 2 - 4" boosters rated at 195 CFM. One at the machine and one at the end. My internal exhaust fan has been removed.

Venting through the roof is ideal. I don’t think you will have to worry about a charcoal filter.

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Thanks for sharing your experience! I also removed my internal exhaust fan due to the noise (best mod ever) and no charcoal means less operating expenses which sounds excellent!

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I started with the same 4" fan and was having issues. Long story short it was a dirty exhaust vent at the end. I switched over to the 6" one listed here before finding the problem but decided to keep it. I love this thing! my setup requires my exhaust duct to have 2 90 degree bends and even a P-trap of sorts. This fan has been amazing. I run it 2 steps below max and things seem to be venting great. There is about 2.5 feet of duct before my fan and about 6 feet after.

I don’t recall if I found this listed or contacted the company but they say the steps for the 6" fan CFM are 44/88/132/176/220/264/308/351. I hope some of this helps and best of luck with your new adventure!

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