I’ve never seen where someone explained why using both fans is not a good idea. I get the reduction in noise from the internal fan, but is that it? Would it cause damage or something to the unit? Or is it really just about the level of noise?
Main advantage of the inline exhaust fan is the reduction in noise. Can you opt to run both, the inline and the internal? certainly. Will there be a benefit to running both? I highly doubt it. The limiting factor will be the volume capacity of the exhaust duct; you can only move so much air through the hose. Most (from what I have seen), use the 6” inline fan, which already exceeds the air volume capacity of a 4” duct. In other words, the volume of a 4” duct is already maximized.
If you don’t care about the noise of the internal fan, why bother with the expense and time to install an external inline fan? If your only goal is to maximize the exhaust volume, I can’t see how an external fan will really help. If your goal is noise reduction, then an external inline exhaust fan is the answer.
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While the noise level of the inline fan is a HUGE plus , the greatest advantage over the internal fan is that it is drawing air out instead of pushing it out. This greatly reduces the amount of fumes and odors that are present in the room. No matter your best efforts, the duct leaks and as @jim.kathy.alexander pointed out the capacity of the fan to move air exceeds the ducts capacity to carry. Air, like liquid will travel along the path of least resistance, add this to the increased pressure and you will have smoke, fumes and odors escaping at every opportunity until it reaches the end. If you will place the inline fan at the end of the ducting where it only pushes out the window/wall, all of the air being expelled was pulled along its path.
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I have an external fan ( 6 inch) but have been running the internal as well for a few months. I originally bought the external fan to reduce the noise and provide an alternative to the internal fan that was becoming a pain to keep clean. I ran with only the external fan for a long happy while. Then that forge died and the while the replacement is still under warranty it still has the internal fan in place.
Thus, I am running both. I hate the noise but fear not running the internal fan will result in a rapid growth of gunk upon it, leading to the need for removal sooner than later. I think the warranty on my replacement forge is just about up so that surgery will happen as soon as the next big cleaning.
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Just a little side note of FYI
with the external fan (switch set to off) when the Glowforge is ‘printing’ the internal fan is still on (at a slow speed, to aid in smoke movement)
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thanks. I might brave turning it off now. It will be excised eventually.
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I think it is just unpowered, but in either case I would expect that there would be less buildup with it freewheeling than powered up. What I have noticed is that the faster the smoke is moved out of there the less time it has to settle on stuff and the less buildup occurs YMMV but perhaps a third as much as before.
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I appreciate the breakdown, thank you.
I just got my replacement unit and for some reason I can no longer turn off my internal fan (I have an external set up) - what am I missing here? Can I no longer do this? ! Picture of where I used to be able to turn off the fan (as you can see it’s greyed out).Screen Shot 2021-11-18 at 4.37.02 PM|406x500
Double check that you’re online with the correct machine (there will be a drop down top right that shows all your machines). If yes, then either open a support ticket in the P&S section, or send them an email and they can fix that on the back end.
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For sure!
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You can turn off the internal by telling it you are using the filter
It’s greyed out for some reason and won’t let me! I’ll try support and see if they can fix it.
understood. I did that with my original forge.
I’m curious if this can be a replacement for the exhaust fan? Mine stopped working and they basically said I need a new glowforge, but if this could be a replacement I’d much rather spend $30.
I haven’t used my exhaust fan since I got my GF. I keep saying I’m going to remove it, but I haven’t yet and I have had my machine 2.5 years.
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Doesn’t the area you’re using it in smell of burned wood or whatever you’re cutting/engraving? Without the fan it all kind of lingers.
Nope, the inline fan pulls much more air than the exhaust fan would and its vented outdoors.
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I finished my new set-up at my new place. I’ve got a normal height window instead of the ground-level one from before, so I used some plumbing piping, and acrylic & an insulating tube for the window 
Now that I know it’s working I’ll likely replace the gaff tape with something more permanent.
I’m still using my original 4" Vivosun and my blast gate from @DaveStruve’s design.
and of course I cut the last piece of insulation (going around the fan exhaust and through the acrylic) just a touch short hence the tape there
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When my original machine exhaust died I got a 195 CFM Vivosun that worked well enough except for the smokiest cuts. Now my machine has a working exhaust fan so I used them both when there is a lot of smoke likely. So you will likely need a 400 to 800 CFM machine to not be able to use the exhaust fan on the machine, but they work a lot better and are way quieter.
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