Anyone venting through a building up to the roof? How to configure?

I am in the basement of our school and I need to vent through the entire building up through the roof. I cannot vent through a window because it will go into the other classes above. If we configure upstairs it will still come back into the classess potentially. The only option is to vent upwards through a closet that has the necessary hookup to the roof vent. I am concerned about what type of fan setup I need etc. Has anyone done this or has anyone done something similar? Suggestions?


If you are venting through the roof you need tp make sure that it will move more than 400 CFM air through without pumping it to the floors above. My guess is that you have professional folk reworking ventilation so the school can open safely anyway, so this would be a minor addition.

There are a number of inline fans that could boost the volume to what is needed. Contrary to my expectations the exhaust air is not heated significantly so there is no natural pressure from heat to assist the lift.

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Is there any suggestion for use of a continuous or intermittent fan? Can the fan come on and go off with the unit or does the fan need to start prior to the unit and/or run longer than the unit. My coworker is asking me questions about the Glowforge and I am not sure how to answer those two.

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the fan needs to be running the whole time the glowforge is operating. It does not need to start prior to the operation, but letting it run for a little while after the GF stops will allow it to fully clear out the exhaust run.

I vent through the roof of a 20’ building, using rigid 4’ ducting with a step-up to 6’ at the fan. I use a 6’ 435 CFM Hurricane brand inline fan.


The quality in-line fans take very little power and are extremely quiet, Mine is a hair small so It needs the assist for very smoky situations but I have it run 24/7 to keep the air moving through and keep any dampness out.

I vent through the roof of my house from the walk-out basement through a vacant furnace flue that became available when we upgraded to a high efficiency furnace. That’s about a 30’ rise. Total exhaust run is about 50’. My system works well with 2 - 190 CFM boosters, one a few feet from the laser and the other in the furnace room at the base of the rise to the roof. The first fan plugs into the same power strip that powers the laser so it comes on with the laser. The second one I have to manually switch on when working.
Venting through the roof is absolutely the best option in any situation, most just don’t have that possibility.

This is a good thought worth exploring. Interesting that the closet has a roof vent. Just having that available is a stroke of luck.

@rbtdanforth makes another good point that in using an external booster fan allows you to turn off the internal exhaust fan that makes as much noise as a gas turbine engine. It would greatly enhance the classroom environment!


If you leave your GF permanently attached to an exterior vent, you should leave the fan running continuously. If you don’t, outside air will seep in to the GF. If it’s really hot and humid out, and the GF is in airconditioned splendor, the inside of the GF will condense water and corrode all your electronics and mechanics. If it’s really cold out, the interior of your GF will be really cold and when you try to start a print it’s going to refuse because of that.

I have a magnetic dryer vent coupler on my exhaust hose. When the GF isn’t running, the hose is decoupled from the exhaust fan. I have a gasketed metal plate with magnets that I place over the open coupler on the fan, to block outside air from flowing through the fan and in to my workshop (which is heated/airconditioned).

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There are other solutions to this. I have a louvered dryer vent that simply automatically closes. Available on amazon for super cheap.

When it’s particularly cold and I want to be absolutely sure (read: I’m being paranoid), I simply open the front door of the Glowforge and close the lid. That makes the interior of the machine open to the room.

No need to run a fan fulltime.


That’s because they don’t really do what you think. Those vent flaps are mostly just intended to keep insects and small animals from easily gaining access to the interior of your home They do a little to reduce the backflow of air, but they don’t really seal tightly enough to prevent backflow.

The dryer vent I installed has louvers. It most definitely doesn’t keep outside air from coming in. Stops the squirrels and chipmunks and bees/wasps from making a home inside the fan, but that’s about it…

And when it’s particularly cold and you open the GF to keep it warm, you’re also opening a path from the outside in to your home/workshop that’ll increase your heating bill.

I strongly encourage everyone to implement a physical disconnect for their vent hoses and not leave 'em hooked up all the time unless you’ve got positive airflow through the hose. I remember at least one user who posted on the forum about how leaving their vent hooked up permanently resulted in corrosion and failure of their machine. It’s not a question of whether everyone else who does the same thing is susceptible. The answer to that is definitely “yes”. The physics are universal. It’s more a question of how fast your machine will be ruined if you leave the vent hooked up all the time. Louvers may slow it down, but they’re not going to stop it. But not having the hose connected, or keeping it at above-ambient pressure will.

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The seal is quite good, I have no problems with backflow even in heavy winds, three years into things. It does exactly what I think it does. Maybe you have a janky vent cover, mine is excellent.

I will bet a significant amount that running a positive pressure fan is an order of magnitude worse in that regard.

Bottom line is that with my setup I don’t have a backflow problem. I open it up sometimes just in case, but not always. I have never had any condensation issues even once in a very humid part of the world, three years into things. I’m not just spinning theoretical yarns here, this is empirical tested data.



Thank you for the suggestions so far I will forward them to my coworker to see what he can do. Of course our Glowforge was purchased but there was no infrastructure set up at the time to support implementation immediately. I don’t think anyone realized the needs of the device and the obvious issue with venting. I may come back with some more questions but I am beyond happy to learn that other users have vented through a building since the only official manual support is for the short window venting.

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