Been here 4 years and honestly have not even checked it…
We cut almost every weekday…
This is what was in there…
A few bits of stencil material…
Most gets vaporized…
A few bits of stencil material…
Most gets vaporized…
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Not much to worry about then.
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It can’t, there is a booster fan upstream that always runs.
And if the power goes out or the fan breaks without you noticing?
Sorry to be doubting all of these interesting solutions, but there are building codes about these sort of things that are in place to save lives, and usually in reaction to sort type of tragedy.
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I do appreciate your concern 
however you don’t have the benefit of seeing the installation, which I gave serious consideration to the design of - for the reason you mention.
The heater (I have installed half a dozen) normally is vented passively with only a moderate rise in the vent pipe, relying on the principal that heat rises. There is an 8" ‘Y’ at the base of the stack that goes straight up through the roof. That is where the 4" laser pipe and the 3" water heater vent pipe join, at the base of the booster fan mounted to the 8" vertical rise.
The 3" and 4" are pointing up, so in the event of power failure the hot combustion gasses would continue to rise just as they should - and much prefer that route (least resistance) as opposed to flowing down. Hot carbon monoxide would have to drop 7 feet to the laser. That’s not going to happen, because physics. 
I would risk neither.
When I finished this 1200 sqf walkout basement I did it better than what the builder did on the rest of the house. I have a background in aircraft mechanics, and I made sure I’m not going to wake up dead. 
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presumably if the power goes out, so does the laser, but i assume a couple people will probably use a ups backup.
can probably hear the booster fan vibrating the venting a bit, ether way?
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Yes, it’s in the furnace room which abuts my shop.
I cant hear my fan but I can see the hose vibrating when its on…thats how you know…lol
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I would be interested in all of you informed, ridiculously smart humans giving me feedback on 2 things.
- My (ridiculously informal) makerspace is venting the laser through the ceiling using a standard Harbor Freight dust collector fan (minus the bag obviously) pulling it out and an air compressor servicing a bunch of tools in the metal shop and the laser pushing air in. Safe or nah?
- If I owned the house I live in, I would cut a duct just like a dryer vent through the wall to the outside, laser cut a decorative cover for it (or make a cute meditating gnome or something for the front flower bed lol) Is this against code?
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This is what I was going to recommend.
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No idea but some modern houses have insulation and membranes in the wall cavity. If you breach the membrane you are supposed to tape it up to keep it vapour proof.
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In CT that would be a technical yes. We have rules on insulation that date back to the late 70s/early 80s when oil prices and inflation were skyrocketing. So there’s a rule about how much insulation (based on R values) you’re required to have in walls & roofs. An full wrap vapor barrier was (is?) used to boost the R value sufficiently to match the code. If you break it by cutting a hole in it then you lose a couple of points of R value and could (in my case would since they made the number only by adding a full wrap around vapor barrier) drop the value to something below the code requirement.
On the other hand, I’d expect it’s the rare code enforcement officer who would know that anymore or care. People routinely install dryer vents (and bathroom vents, etc) through the walls and pierce the vapor barrier during remodels that do not include stripping the wall to the studs and sealing the vapor barrier back up. It’s also unlikely that a 4" hole in a couple thousand square feet of wall is going to seriously impact the insulation value of your house 
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I was more concerned about the laser exhaust sharing the exhaust for the (I assume gas) water heater.
@PrintToLaser, You are putting a lot of faith in the proper running of that fan to avoid CO poisoning.
I would lean toward the direct to the outside route.
The vent thought the roof could work, but as I have indicated in previous posts, we do not know how flammable the debris is. If it is not completely burnt it is certainly dry and ready to burn. Sparks happen when dry particles are moving.
May not be an issue but why risk it?
Codes differ in different locations but the same basic principles apply.
the 2012 International Mechanical Code can be read for free here, and has been adopted by many local jurisdictions.
I know that there is a tendency among many do-it-yourselfers and Makers to think that building codes are for rookies or laymen but these are intended, in most cases, to save lives, not just make your life difficult.
It seems like a no-brainer to at least try to follow them rather than risk injury or death.
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You could probably foam the bleep out of the hole before inserting your pipe – the main thing is going to be the direct air path.
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The water heater would continue to vent passively, just as it was designed to. The safety of my home is not contingent on the booster fan running.
I set the fan up to run continuously just to provide positive ventilation to the furnace room instead of just passive. (added safety - not dimenished ).
Your concern for people’s safety is warranted, people die who are not aware of the hazard, so thanks, but you needn’t worry for me.
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The only reason why I keep mentioning this is because this forum might be were others seek advice.
You may have considered all contingencies but others may not have.
I would still be concerned with having ANY path from a flue, that is meant to carry poisonous CO gas, to any interior space. Hot air does indeed rise but if there is any pressure imbalance from the shop to the flue or from inside to outside, it could suck the gasses in to your house/shop.
I have seen many cases where the air does not go where you would expect (during a storm, when the air-conditioner, or heater is running, or even when the wind is blowing a certain way, etc.)
Best to separate exhausts from flues.
At the very least, please install a CO detector in your shop. Sometimes people die who are aware of the hazard, but create a situation that is more dangerous than they realize.
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I could also see it mattering the type of climate you live in. In Texas it isn’t real wet or real cold very often… But maybe a well made internal vent cover to keep on it when not in use so moisture and all that stays outside of your exhaust hose would be a good bet
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@marmak3261 had a good homemade design for that. And there are a couple commercial one using magnets to attach that are out there. I don’t know if the commercial ones would leak smells though - they can’t seal as well as a clamp & foil tape.
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I didn’t order a filter. I’d agree if I had.