Extraction is a funny thing, you may also need to consider local laws, it may actually be illegal in your area.
4" soil pipe make for nice cheap long runs, if you need to turn a corner used radiused bends, not short 90' elbows as they screw up the flow rate.
dual domestic hidden in the roof space type inline / axial extractor fans, each capable of 350 cfm, are quiet, low power, and do the job, but site them where you can just swap one out if one dies.
HOW you plumb / attach the suction side of this to your laser is a question in itself, in my set-up one draws air though the bottom of the Z table, and one draws air out from the back of the bed, and for me this works excellently.
May I share a cautionary tale........
video -
https://vimeo.com/album/3052977/video/112489108
related blog post -
How to avoid producing scrap. | Exeter Laser
TLDR version - basically a laser cabinet with extractor fans running can very quickly turn into a forced draught wood burning stove, and even if you have fire and smoke alarms in your workshop, they won't be triggered until the extractor fans burn out or die
Nota Bene this is just extraction, not filtering, filter stages add back pressure, so it gets even more complex... a friend of mine made a wonderfully efficient filter that was basically a big copper water tank filled with layers of foam pellets and auto air filter paper and so on, incredibly efficient as a filter, then one day the whole lot caught fire, so now he had added an intercooler stage, which also needs cleaning, his complete filtration setup is now twice the size of the laser, and about 30% of the cost, but he has no alternative, thanks to legislation applying where his laser is sited.