As you can see above I got the 190 CFM fan. I would prefer more but cannot find more than 205 for four inch hose at almost double the price or more. I looked at the other 100-cfm but the drop in price was not worth saving $7 for half the CFM.
The Blu-Dri has output plugs so one switch can rule them all even if the main fan is off. So I leave that plug turned on most of the time so room air is moving through the Glowforge most of the time, and kick on the blue whale at the lowest settings when actually cutting, and letting it run for quite a while after getting rid of the slightest stink.
When room air is moving through, it is not outside air, and therefore drier.
I think I have the same 4" fan as @rbtdanforth, it’s quiet enough to run the entire time the machine is powered, and has worked effectively. I’m also surprised and happy to report that it seems to do a good enough job by itself since my built in exhaust fan failed - and I haven’t removed the grill yet. I have no leaks and have not needed to tape up anything. I run the provided duct to the fan on the floor, then another 25’ of hose that I either throw out a nearby door, or run to a window. It’s been the door for 95%+ of my use.
Even now that the OEM fan is available, I don’t think I’m going to bother replacing it - certainly not internally given the hassle to get at and clean effectively (I have a pro, access is extremely limited). If I find the external duct fan insufficient, I will go with either an additional (identical) 4" fan inline, or something larger built into some kind of housing.
It sure is nice not having what amounts to a 747 engine running when the machine is busy printing!
I found that most of the time it was sufficient but when cutting oak near the front it would shove smoke out the pass through particularly if I had an over-sized piece stuck through and covering most of the crumb tray screen. Under those conditions having the crumb tray screen open in the front and not much room for the smoke leave any other way was quite problematic.
Fortunately the Blue Whale saved the day by feeding off the the smoke almost as fast as it got away and finished off the crumbs of the meal within the hour.
When your Glowforge is properly set up, you may have some harmless odor during printing which will rapidly dissipate. You may also smell something when you open the Glowforge lid after a print is complete. This is not harmful.
However, if you detect a strong, sharp smell that also causes eyes, nose, or throat irritation, or if there is visible smoke escaping while the lid is closed, shut off your Glowforge unit immediately. Smoke and fumes could be entering the room in excessive concentrations.
