How long a run before booster fan needed?

I’ve searched but I’m not finding what I need. How long a vent run can be used before you need a booster in-line with it?


There is no firm number. Anything longer than the provided duct, and two 90 degree turns, and “you’re on your own” - support won’t go beyond that.

In reality, many people have had success with longer runs, and then there are some that have had issues even with the short provided duct. Your mileage will vary.

I personally run a cheap inline fan, which happens to be the only fan now that my stock exhaust fan died. No issues. Oh, I have a total of 35’ of ducting.


Ok, thanks! I’m running a straight 25’ after moving my laser. I haven’t tried it yet as I didn’t want to burn out the internal fan.

You won’t damage the fan unless the duct is so restrictive, you have smoke blowing out of the gaps on the machine.

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For 25 feet, you almost certainly will need an inline booster. That’s a long run for a clothes dryer, never mind the GF. The GF’s fan is only 4". I doubt it has the “torque” to push that far. Especially given that dryer hose is “ribbed” so it doesn’t flow all that well to begin with. I’d be surprised if the GF ventilation system will work as well as you want it to. The GF has an inlet fan that’s the same size and if the exhaust isn’t moving air at least as fast as the inlet, smoke will be driven out of every seam in the machine enclosure.

And you could damage the fan. Because the long hose run is going to offer resistance that slows the airflow down, the pressure in the hose will go up. So the fan will be working in what is effectively denser air and as a result, the load on the fan will go up. The GF fan doesn’t appear to be anything special, just a fairly run-of-the-mill computer boxer fan. These fans don’t like working against a high head of pressure. They want to be blowing out the back of a computer enclosure with nothing more than a finger-guard between them and the ambient surrounds…

A booster fan will pressurize the duct downstream of it, so it is best to locate the fan as close as possible to the end. I would recommend you seal all the joints in your exhaust run, including the booster fan housing.
I found caulk to be a quick and effective sealant.

I have a long run, and the room is odorless.

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Not to be argumentative (too much butt-hurt around here lately!) but I have my cheap 184CFM-rated inline duct fan at the end of the provided hose, with a 25’ hose from there. All connections with simple hose clamps. I’ve been running it that way for almost 2 years and when I have the outlet a few feet from the door or window it’s been tossed thru, I get no smell inside.

Now that my internal exhaust fan has died, I’m also pleased to report the external solution is sufficient. I’ve done a few long wood engraves and also cut acrylic and, yes, I can detect an odor when I’m next to the machine, but that’s it.

I’m not implying anyone is doing anything wrong, I’m just sharing my experience - that it’s not necessarily hard or expensive to set up an effective venting solution.


Glad that external vent solution worked for you. :+1:
Most of my run is the standard 4" sheet metal vent pipe. I couldn’t lose the smell, soo I sealed every joint and side seam in the run and the smell disappeared (the booster housing leaked too).