AC Infinity S6 versus AC Infinity S4 fans

Would the AC Infinity Cloudline S4 fan be sufficient since I only run the glowforge about an hour a day? The Amazon descriptions show the S4 is quieter at 28db vs 32 db for the S6. And $20 cheeper and wouldn’t need the 6" to 4" reducers.

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Yeah, that’s even 10more CFM than the one I’m using, so you should be fine barring having an excessively long/complicated run (greater than ~15’ or more than 4 turns)


FWIW I’ve been using the same one as @deirdrebeth for a couple of years and by itself since my internal exhaust fan failed a few months back. I agree, you should be fine.

i don’t have either, but one of the things i’ve seen people who have the 6" version say is that the larger one doesn’t need to be run at full speed, so it’s actually a little quieter than running the 4" version.


Just curious, what’s the problem with using it for long/complicated runs?

the longer the run goes and the more changes in direction, the more CFM you lose by the end of the run.

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(edit - I thought by “length of run” you meant longer print jobs, sorry!)

The fan speed is not changing. There’s no loss in performance no matter how long the job runs for. Smoke is drawn to the left and out the back no matter where the head is or what direction it’s moving in.

I bought the S6 and it’s great. I wish, though, that I bought the S8. Only reason I didn’t was that the ACInfinity salesperson said they don’t recommend reducing from 8” to 4”. I shouldn’t have listened. While the S6 works pretty well, I do still get some smell in my office. I have a window screen that I can’t remove and I believe the window screen is limiting my flow rate. Since I can’t remove the window screen, I wish I bought the S8. I have the feeling if I cranked it up, the dust wouldn’t collect in my screen anymore and I’d have a room that doesn’t smell like campfire.

So why did I learn all that pesky physics around frictional losses & flow? Sheesh, I could have partied way more.

While conservation of mass argues that the CFM at the front & the end of the hose need to be the same (no air is created or destroyed simply by transiting the hose), the ability of the fan that is pushing the air gets impacted by the pressure being created in the downstream hose. Unfortunately although the models usually treat air as an incompressible fluid (it’s not, just that it makes the calculations messier) and the pipe as friction free (again it’s not for the ribbed hose we tend to use and with the gunk that builds up on the walls along with the impact of angles and curves vs a linear run).

Effectively you get less air transiting the system as you add length, ribs, gunk and changes in direction. The fan may be rated at 200CFM in free-flowing unrestricted air but it won’t achieve that in a sub-optimal installation that characterizes nearly all of ours.

I assumed by “length of the run” he meant the print job. My bad.

I’m using a 4" vivsun(sp) with 35" of ducting.

Well he’s technically incorrect - you don’t lose CFM “by the end of the run” as it was never there in the first place. If you’re stuffing 200CFM in on the beginning it must come out at the end and in a rigid or semi-rigid tube that does not swell and create additional tubing volume to store the extra air, the friction causes pressure increases which will slow the fan down at the beginning of the run. You’re not putting 200CFM in and getting 150CFM out. The fan is rated for 200 but may only be pushing 150 or even 100 or less depending on what kind of restrictions are in the pipe. HVAC guys deal with this all the time. Fortunately (sometimes anyway) ductwork often leaks like a sieve :slight_smile: (the bane of my father’s existence when I was a kid - he was in HVAC).

right, but in the end you’re not getting the full 200cfm out because the fan can’t push that much volume over that much distance in that much time along that tube. probably even moreso when the tubes aren’t completely flat along the sides.

i don’t know that a higher CFM will make as much difference as you think. you’re still going to get a lot of buildup on that screen. it will eventually clog, and every time you run a job, you’ll get a little less throughput as more particulate sticks to the screen.

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In your case, I would consider building a box that can house a cheap HVAC filter, then vent thru the window and screen from there. You want a cheap filter because you want to keep the obstruction to a minimum.

Yep that’s especially true with the thin ribbed foil dryer hose. A bit better with some of the more robust aftermarket hoses. Also one of the reasons the forge is so loud - most people have a fair amount of turbulence in there from the rubbing & the direction changes. Worth upgrading the hose (including to one of the insulated ones to cut down noise). Someone here (@PrintToLaser?) did an install with PVC pipe that’s likely got much higher throughout but I think it was a long install & had a booster fan on the end.

Nope, that wasn’t I, my run is the standard 4" galvanized vent pipe with the exception of a 3’ section of the clear flexible vent hose that allows the pull-out action of the glowforge in a “drawer”.

Since I removed the exhaust fan I now have 2 boosters, one at the rear of the machine that the flex vent connects to and one at the end of the galvanized run.

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Hmmm…you made me go look. It was @dwardio

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The difference in dB is negligible. The motion system of the Glowforge itself is around 55dB. Both fans are quieter than the Glowforge itself running in CF mode.

While neither the S4 or S6 do great with static pressure, the S6 is able to draw more vacuum, which ties into what @jamesdhatch was mentioning with losses inherent to the system, which means it’s able to better overcome some of those elements like bends in the tubing, frictional losses, etc.


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