Can't work out why its not venting

HI Brain Trust,

I’m hoping to get some help. I’ve had my glow Glowforge for nearly 2 years now, and after recently moving apartments, I thought I’d hit the jackpot getting a basement with a window! But for some reason, it’s given me more trouble than I could ever imagine, I have piped the Glowforge out the window with an in-line fan yet whenever I cut any material, the PM 2.5 and VOC in the room skyrockets almost immediately up to about 50-100 and the smell is really strong.

I’ve checked all the connections, I’ve checked all the pipes, I’ve sealed the window and the entire frame from the inside and the outside and for the life of me can’t work out what’s going on.

I’ve read about switching to a PVC pipe (the air-con ones) but they look thinner than the AC Infinity 4 layer ones - the AC Infinity ones have a PVC outer layer too. Or do people mean a PU pipe?

Does anyone see anything wrong here. (Images Below and Video with Dropbox link)
Video Here

Thank you!


I had that setup for a while and found it was impossible to seal the “escape window” enough to keep fumes from re-entering. That may explains the issue with cutting acrylics you posted about.

If you could run the external exhaust above grade, that would probably help, but might annoy your neighbors in an apartment complex.


I would also check the machine itself. I had mine on a shelf that wasn’t 100% level, and somehow the position of the GF “skewed” the lid just a skosh and I had some smoke escaping the front of the machine. I only suggest it because you say you just moved the machine.


It looks pretty close. I would say it actually looks really good but you’re smelling stuff so clearly something is amiss.

There are a couple of ways that smells can get into your workspace. This is all general stuff and it may be basic, so I’m sorry if this is stuff that you already know but fundamentally ventilation is a fairly simple situation.

First you need to look at places that might be under positive pressure. Generally that means things that are after a running fan and before some sort of a blockage or resistance.

So you have three fans in the system that are relevant here. One is the intake fan on the bottom of your Glowforge, two is the Glowforge internal exhaust fan in the back left, and three is your external fan.

The intake fan pulls air into the Glowforge case and if you are impinged on the way out, it can lead to a positive pressure in the Glowforge itself and smoke will escape through the cracks in the Glowforge. This is typically caused by a dirty exhaust fan, so it can’t work at full capacity.

If you have that fan turned off in the Glowforge interface, it may still be a source of resistance if it’s a dirty fan. So now your intake fan is pulling too much air and it can’t escape the glowforge quickly enough. I would take a very careful look at your exhaust fan and make sure it’s nice and clean.

The second place where you may have positive pressure is between the exhaust fan and your in-line fan. This could be caused by having a kink in your hose from a bend that is slightly too sharp or it could be caused by the internal resistance of a particularly long hose run — which I don’t think is your issue here — or it could be caused by not running your external fan at a high enough speed or a problem with your external fan in general.

For that, I would take a close look at your exhaust fans to make sure they’re both clean, take a look at the inside of your ducting to make sure that there’s nothing stuck in there or otherwise dirty, and make sure that there’s no kinks impinging airflow between the back of your Glowforge in the front of your external fan.

And the third place that could have positive pressure is anything after your external exhaust fan. Check very carefully to make sure that all of your seams are tightly taped and sealed, and also be wary of bends that are particularly sharp. You do have a 90° bend in that hose, but it doesn’t look like it’s kinking the hose. I think you ought to be OK but I’d check it.

If all of this checks out, your fans look like they’re functioning properly and not blocked, your hose looks like it’s running as smoothly and straight as possible without any tears or impinging… Then you have to wonder if you’re sucking fumes back in from the outside.

You’re pushing air out of your room, so more air needs to come into the room to compensate for that. It’s got to come from somewhere, and if there are any gaps in your window set up, you’ll be pulling fumes right back into the room when the Glowforge is running. Your window looks fairly well sealed with all that tape but windows are notoriously hard to seal completely.

One possibility prevent this is to extend your hose out past the window, to make your fumes further away from where they might get sucked back in through cracks. I see that you have an extension that goes out about 6 inches from the window, if you can extended a little further that might help. If you want to see the ultimate set up you should check out @dwardio ’s post. His set up is what iview as the gold standard, it uses hard pipes to reduce internal resistance and vents above his roofline. I’m still pretty jealous about that even though mine works really well.

Anyway, it looks like your set up is pretty good. I feel like you’re going to find the one thing that is a gap and you’re gonna fix it and be happy.

So, that’s a lot. How to narrow it down so you don’t have to take everything apart? For me I would work backwards and use incense to help find where the leak(s) might be happening.

First, test the window seal. Set up incense right outside the window of your workshop, then run the external fan and Glowforge at very low power while not lasering anything… And run it for a while and see if you start to smell the incense inside. You would know for sure whether or not you’re sucking in from the outside and can concentrate your efforts on the window seal.

If you run it that way and smell no incense indoors, then it’s not your window seal. Next up test the external fan. Turn off the Glowforge entirely but crank your external fan to whatever level you normally run it at. When it’s pulling air through the Glowforge, light some incense on the bed of your Glowforge. It should immediately start sucking the smoke out through your exhaust close the Glowforge up, let it run for a while and see if you smell the incense in the room. If you do, it means there’s some sort of a leak between your external fan and the window.

If you pass that test, next step depends on whether or not you’re running the internal exhaust fan in your glowforge. If you’re still running the internal fan, then the best test is actually something kind of unconventional and would require disabling your safety interlock. You want to be able to run the Glowforge with the door open… Then once it’s running, do the incense test by lighting incense on the bed of your machine. This will prevent a buildup of pressure inside the machine from your intake fan. Let the exhaust fan run with the external fan… If you have both positive pressure between your Glowforge exhaust fan and the external fan and a leak between the two, you would start to smell incense at this point.

If you pass all three of those things then you know the problem is that your internal fan is making too much pressure inside the Glowforge and you’re starting to see leakage from the cracks in your machine. At this point you have to figure out why your airflow isn’t adequate even though you have two exhaust fans running.

Anyway this seems like a fair amount of work, but if you’re very sensitive and really need to make sure this you’re set up is perfect, this is how you’d do it.


Could it be something as simple as because your exhaust is sitting inside of what looks like a window well and the smoke is just hanging in there and seeping back in? I know that mine is at ground level (I have a walk-out basement, but where my GF is, I have it vented out a window at ground level) and when the wind blows from that direction, I do get a lot more smoke/smell back in my room. I can also see more smoke inside my machine when it’s really windy, so I tend to not use it on really windy days.


I am also venting our of my basement window. I have a 4to 6 inch 90 out the back of the GF . Found out that the fan on the rear of the GF was looking bad. Had to remove it.


Thank you, this was fantastic information. I shoved my phone torch inside the 6” ac infinity pipe going from the external fan to the window shining it up towards me from the inside and it looked like the night sky. I could see the light from my torch almost at every point. Some points were a dim brown spots that looked like when you hold your phone under a piece of paper but then there were all this bright white spots that looked like pin holes. There were not actually tears though.

I thought surely that’s just because the iPhone torch is so powerful. Then I did the same with a brand new 4” ac infinity pipe, also the black one and couldn’t see a single thing dot.

I’m assuming it should be the same on the 6”, should be totally black and you shouldn’t be able to see the iPhone torch from the outside….?

Also do I actually need a blast gate, again something new which I didn’t realise I needed? I am about to add one of those grills with the flaps that open and close but I really don’t want to unseal the whole window again so I’m tempted to just leave the open pipe exposed.

It is a basement well, I originally thought, oh I’ll just hand the pipe from the grill above and vent straight up, obviously that wasn’t going to work because when it rained it would be a hose into the Glowforge :joy:

I’m in Switzerland so we get snow and rain in winter, do I need the blast gate?

Lastly, I see people doing from the Glowforge immediately to a 6 inch hose with that adapter vs what I have. Does it really make a difference? Because buying that adapter from the US is going to cost at least $70 with shipping plus another pipe.


I strongly recommend one. It will help keep your GF in the recommended temp range, reducing time lost to allowing it to warm back up. I live at 1500 meters in snowy Colorado and keep mine shut anytime the temperature drops below 0°C.


They sell alot of those pipes at your local building supply stores. That’s where i bought mine after seeing the prices to have them shipped from the US. When i lived in the US, i bought the adapters from Home Depot or Lowes (home improvement stores), and here in Japan, i bought them from the same place that sells tools and hardware.

Also, to add to your check list, in the past, I’ve had air coming back into the room for reasons other than blocked fans. I have pets, the the intake on the right would often get blocked with fine hair, causing overheating errors. But also that same fine hair blocked the rear exhaust grate. So even if my fans were clean, air wouldn’t pass- and i couldn’t see this because the hair made such a thin, fine net. And the part that vents outside, i used to have a screen there because i didn’t want insects and animals coming in. The exhaust buildup on the screen would stop air from escaping, even if it didn’t look that dirty to me.

So when i cleaned after a project, i would be cleaning air assist, rear grate (because i ended up removing the exhaust fan), the external fan, and the screen where my exhaust hose was touching. My previous home had terribly insulated windows, so no matter what i did, there was some smell that made it’s way back in, but never unbearable if all else was clean.

I would say that when it rains or snows… you might just want to unhook your machine and close your window… would the rain pool in that well area and get into your home? Blastgate would help, but not sure how helpful if a flood of water was coming in- someone shared a file on the forum for a blastgate they made themselves from acrylic. But i think adding one of those little hoods that direct airflow to the outside of your setup would be helpful in blocking incoming rain and snow… again, not helpful in a pool of water though.


I prefer a louvered vent to a blast gate. It stops backflow and critters and it’s completely maintenance- and hassle-free.


So I went to the hardware store here the other day before writting this post and looked at a few things.

  1. a Louvered vent - this was super weird, they had a plastic one with the back diameter (where the host goes) of 156mm but the largest hoses they had were 6" at 150mm. They had a aluminium one that was 145mm at the back, so the hose sat nicely over that but it was aluminium which I didnt really want.

Question, once it is pushed up against the acrylic, how are you a) holding it there and b) sealing it around the edge so the smoked doesnt come back in around the side and through the hole in the acrylic around the side of the pipe?

156mm One

145mm One

For pipes they then had this shitty AirCon ones that looked like they could puncture at any moment, so I was confused as to why everyone was saying go with PVC over Aluminum since most of the Alu are covered with PVC too. They had an Aluminium one which was serious aluminium, i.e. I tried to put a hole in it with my finger and it just made a dent. You really would need a nail to pierce it, I didn’t get it because I have never seen anyone suggest those.


Aluminium one

But they are the only two they had. So I went on Amazon and found this PU one, which I was wondering if that is what everyone mean…

I then also found these:
Flap Vent

4" to 6" Adapter (because I cant get the 3D printed one from the US), not sure if this will fit though

This pipe because I couldn’t get the AC infinity one

Its very annoying that in the US you can easily get all this stuff but as soon as you are in another region it’s super hard. Makes me want to get a 3D printer and start to sell them myself.


Here’s what my setup looks like. I used a dryer vent hose with a louvered cover out the back. I do have a blast gate on mine inside the house to keep the drafts out; the louvered cover outside helps with that too, especially since our winds normally come from that direction. I’ve had mine up for 2 years now and haven’t had any problems, unless the winds are really strong. We did replace the lower glass with 1/4" plexiglass, but we own the house, so we can. If you’re renting, you might be able to check to see if they’ll let you do that. Then we just used waterproof silicone to seal the edges of the vent and the window.



Hope you get yours worked out!


Gotcha - when at least I am saying PVC, I mean a pipe rather than a hose.

You can’t see through it, but debris is never cutting through it.

I did use one like your examples (that came with the machine), but it punctured pretty quickly. I replaced it with an insulated one - exactly the same exterior, but the inside had like 20mm of insulation so it was stronger and quieter, but more stuff got stuck in it, then I moved to the pipe.

For connecting (you can see it in the picture) I use gaffers cloth tape. Lots of folks use duct tape. Anything meaty enough to hold them together without tearing over time will work :slight_smile:


Here is a video of my starry night hose… any one else’s like this?

Some of it looks more just like cracked PCV on the top than holes but I can’t tell.