Exhaust Options

I’m building my :glowforge: space in my garage which doesn’t have any windows. The only exterior wall leads out to the street at head height and there’s only our drive between the house and the road itself. As a result, I’m not keen to send neat exhaust out that way. I have a washing machine in the lab / workshop which obviously pipes waste water to a soil stack… can anyone think of a reason I couldn’t send exhaust into the sewer? :confused:

If the exhaust is considered toxic then it it probably illegal to put it into the sewer. There are lots of chemicals that you are not allowed to pour down the drain. I presume because it would either kill the bacteria in the filter beds that digest the sewage or get thorough the filtering into the recycled drinking water.

You would need an airtight blast gate to prevent the smell of the sever coming out through the Glowforge.


Hmm I can’t think of anything in there which would kill the bacteria (at least not in the quantity I’d be putting down there - it’s just too little to make a difference). Heck, the company I used to work for used to send them low levels of potassium cyanide (with permission of course)!

Backflush through the :glowforge: is very good point mind!


The plumbing vent pipes are also small diameter compared to the 4" exhaust.
Around here we have radon mitigation systems that vent the crawlspace, I was considering that route at one point.

Soil stacks are 4" pipe here. The water pipes are 40 mm (or thereabouts). There’s an adapter which links the 40 mm to the 110 mm stack, so I can adapt it. I’m just not sure I want the Glowforge to smell of poop…


Do not combine with waste vent, radon vent, gas appliance vent, or really any other type of vent.
A connection to an existing vent could allow back-flow even with a booster fan.
If connecting to a waste vent stack you could expose yourself to these bacteria (like legionnaires disease).

Connecting to a radon vent is also a no go. Radon is very heavy compared to air and the Bernoulli effect and/or a booster fan can only work to lift the radon if the top is the only path out. Otherwise it will always drop to a lower level, defeating the purpose of the radon vent. Usually a radon vent also has a suction alarm to indicate if there are leaks in the pipe which would also cause it to fail.

Connecting to a gas appliance could allow CO and/or gas to back up into your laser/workshop. Turn on the laser and BOOM.

If you are not using a filter I would recommend a unique vent for the laser that goes up through the roof, out of a side wall, or out through an eave. If the length is long enough to warrant a booster fan I would place the fan near the end of the run in a location where it could be serviced (unfinished attic space for example) or add a service hatch. I would use smooth duct for all ducts that are hidden in a wall or floor (flex for the exposed part of the connection). The system should be designed in such a way that it can be cleaned with one of those pipe cleaner looking duct brushes.
I have posted here about how long of a duct run could be before you would need to use a booster, and how to calculate the effective duct run.
Not much is really know about how best to vent these, as the :glowforge: is the first large scale deployment of lasers for home use. What I recommend might be overkill (I have been called alarmist by others on this forum), but I would rather be safe than sorry.


I was going to let you know that without a backflow preventer, when the wind blows you will get that ode de fragrance :poop: into the GF :glowforge::nauseated_face:.

On a more serious side, I want to say that the Plumbing Code and the HVAC Code don’t allow shared connections.

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people really don’t seem to care; i still think this insistence on just attaching the exhaust to a chimney is an awful idea.


I was talking about the connection to the sewer not to a chimney, but I’m not insistent on it. I was just seeing if there were good reasons not to do it, and it seems like there are.

and i wasn’t talking about you, dude, sorry.

Oh - oops!

I’ve had a mooch through the interwebz looking for external air scrubbers as I figured there’d be a market in standalone units with the uptick in laser cutter sales. I was sure a Chinese company would be selling them by now but so far, nada. Maybe this is a business opening…

My worry with the official :glowforge: model is that it’s just going to add yet more stuff I have to buy from the US which is going to make the unit less economical :frowning: - I guess I’m building on myself then!

you’re not wrong but on the plus side replacement filters should be relatively inexpensive to ship, as they’re going to be pretty light in weight (especially relative to anything else you’re likely to be ordering from glowforge).

i’m still a little bit skeptical that they’ve revolutionized the filter itself (i mean the replacement media that fits inside the large filter container, which, viewed in the absence of any information, could potentially be very, very cool) - if that’s the case, you might see affordable options from third party sellers / manufacturers who are more local to you.

i have no problem with chinese build quality generally speaking (how much of all my technology is built there after all) - they’re just the new korea is the new japan from that point of view. but given how awful the affordable chinese laser cutters are*, i’m not so sure that i’d trust a similarly made air filter.

*= and the good ones aren’t any cheaper than a glowforge.

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On the postage front we pay a lot for big light items as they take up space. I can’t see these being small. Plus, tax is horrendous!

We work with this kind of filtration at work and they always work better when the filters are employed vertically; the exhaust takes the path of least resistance and lying filters down just allows the charcoal to settle and a small gap to open up which the gas then follows. I’m not sure how they’re going to make it efficient given the likely horizontal orientation. I’m not saying it’s impossible as I have no clue what they’re doing, but I’ll hang on to my cash fort he time being methinks.

Some good how-to guides on instructables which will give me a good start mind.


for sure - in your case i think that that pre-filter before exhausting outside would be ideal; i don’t trust any of the diy filters to be safe for venting indoors, though.

Agreed - I don’t want my tombstone to read ‘breathed his own fumes’ …people might get the wrong idea! :laughing: