Inline fan box: Make it silent


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My grow spot is small. It is a under stairs room. My supplies weren't real extravagant, small carbon filter, 4in inline fan, cheap LED light, nothing crazy. I lined my room with 1/2in foam board. I was hoping that this would create a descent sound barrier. The day my equipment finally arrives was super exciting, until I plugged in my inline fan. Holy shit that fan was loud. Loud enough that anyone in my basement would ask what that noise was. Loud enough that I would have to have the TV louder than norm just so I could drown out the inline that is just a few feet away. I now had a new mission. I didn't want to hear my fan at all. It would REALLY bother me if that was a constant sound running around my basement. Time to find a solution.

On another site I saw a thread of a fellow who built a box around his inline and made it so quiet you could not hear it at all. Oh, Snap, thats what I'm talking about. I had to do this. Here is what I have done. This is a project that is not 100% finished yet, but will be on Monday.

I first made a fully rigged box of old plywood. Now I am not a carpenter so my design is REAL rudimentary. I used a table saw to cut a 2x4 in half, I didn't want to try to screw into that 1/2in plywood and split it all up. This box was very cheezy and not really as well designed as I would have liked, but it made a good model to begin from.


I used a small hole cutter on top to get access to the mount on my fan. I was going to hang this from the ceiling. Once I had it hung for reference, I realized that this was too much in my room. It was really in the way of my LED. My wife checks this out and asks me why it isn't on the floor? Well thats a good damn question. In a basement stairs setup you have some wasted space due to the angle of the stairs. I can work with that.


New setup has begin. This will sit on the floor and I am going to run insulated ducting from carbon, to box, to exhaust. My supplies are as follows.

3/4in MDF board - comes in a 4x4 sheet which is plenty

Table saw, circular saw, jig saw - whatever floats your boat to cut material

wood screws and washer - this was my original plan but as I will show later I have changed this out


extra foam board - use this as some more sound proofing. I don't want to hear this fan at all.

I made the box big for simplicity. The top bottom and sides are all 16in boards. You screw them together as you wish. After I screwed in the fan to the bottom piece I lined up one of the side boards. Remember, to do the sides you must account the extra length which comes from the width of the boards. My 16in boards when made into a box will have an extra 1.5inches in length or height depending on how you screw the box together. I lined up my side to drew a semi circle from the fan itself. To cut the side hole I raised the line to start my hole 3/4in, to make up the difference because my side was not flush with the bottom of the box, it was sitting on top of the bottom board. I do not have a 4in hole cutter so I used a drinking glass that had a 4in opening for a template.


After I had the sides connected I used some caulk to seal the seam of the box. I want this air tight. Next I used a piece of extra foam board over my hole and caulked it to the inside of the board.


I then connected my ducting to the fan and pulled it through the hole. I calked the inside of my board and screwed it together. Some caulking came out after it was screwed meaning this is sealed shut.


I bought supplies yesterday to change my box. I am ditching the wood screws and washers for a bolt with rubber washers, a rubber sheet, a fender washer, lock washer, and a nut. This will not sit on the box as it is now, it will hang. After running the fan I noticed a loud vibrating sound. When I pressed on the fan the vibrating went away. On Monday I will post some pics of the finished project. Essentially it will look the same, just flipped over. Once this is done I have some extra foam board that I will caulk to bare sides. I also have a piece of cardboard that came with my fan caulked to a hole side for more sound proofing. When I am done my fan will be silent and perfect.


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So yesterday I mounted the fan to the box with my bolts. I wanted to punch myself in the face for not actually taking off the mounting bracket and bringing it with me to pick out the hardware. Of course the bolts I purchased were too wide to fit into the bracket. Spent 20 some minutes filing down the inside of the bracket slit, but my bolts finally fit. Bought a larger pad of rubber that went on the underside of the mount, and a rubber washer to go above the mount. I did not want any metal touching to keep vibrations at a minimum.



Today will be hooking up the insulated ducting to the box. It is incredible how quiet the fan is once the ducting is in place. Depending on how the room goes I may eventually move the box to the outside of the room. Today I will take a video on how the fan is right now with just the elbows attached. I will do another video once the ducting is attached. This was a very rewarding project.

BTW, ever find anything in your room and ask, "How the hell did that get in here?"

I found a frog in my room yesterday....



New Member
Of course the bolts I purchased were too wide to fit into the bracket.

Story of my life lol. Looks good man! Wish I had the kind of space freedom with my setup to do something like that. Just yesterday I installed my fan and found myself in the same predicament. Luckily it's overkill for my setup and with a controller I can turn it down and reduce the noise significantly while I'm in the room.


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I have completed the my task. Room is very quiet. Had my brother-in-law over and he had no idea fan was running not 5 feet away. The exhaust is also whissssssper quiet. I just have a 4in hole cut in my wall and there is no sound of the air coming through. I have a grate ready to go over exhaust hole but the air passing through the grate makes too much sound for me. I am going for as silent as possible. I am very happy with the outcome.

Here is Dr.Octopus. He now resides in my room. So far he is a peaceful chap. I was originally going to make some sort of box to hang from my ceiling. My wife made the call to put the fan in a box on the floor. Very good idea. Had to make a longer run of the insulated ducting but this is what is keeping my air noise to a minimum. That ducting is like a silencer on a pistol, sucks out all the noise.


There is my 4in carbon and exhaust.



Time for a test run. Today was my birthday so we celebrated it in Detroit. Went to Autorama and Greektown. Good times. Before we left I placed a full reservoir in the humidifier and placed it near my intake. Lets see where RH is while out and about. Just hung my meter with some duct take, trying to get plant height.



Came home and saw that my RH is now in the high 40s and climbing. It sat at 30+ regularly. After the RH went up time to turn on the light for a over the night test run. Used a box to simulate some plant height for meter. By morn I will have a good idea on temp and RH. If I can keep temp good with light alone I shall be a happy guy. I don't want to also plug in a heater, but I may have too. Good times a coming!!!



Member of the Month: Jan 2016, Aug 2017 - Nug of the Month: June 2017 - Photo of the Month: Sept 2016


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Good man , I noticed you put down some rigid insulation on the floor. KICKASS for your plants tender roots.

You have done a great Job with this , as well , success is sure to follow with such attention to detail.

Yeah man, thx. Everything is going super good. I had to put a small heater in the room for temp and all is dialed quite well. Space is small and I'm new so only 2 plants for me right now. This is impressively stealth.



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Did you end up putting something inside the box for acoustics?

In one of the photos you can see the insulated foam that I caulked to one side. On the other side I used a large piece of cardboard that came with the fan. This piece had a hole cut-out that covered one of the inlet/outlet. I used this piece and caulked to the other side.

In hindsight I would make a smaller box and I would use more insulation. The only place you can hear this fan is really when your walking up and down my stairs. You reach the bottom of the stairs and the sound just disappears. You turn the corner from the top of my stairs and enter my kitchen and poof, sound disappears.

Awesome job man! Who needs to buy a silencer!!


Thx! I am still trying to utilize that space to the max so I may end up moving the box outside of the room. I can plug the carbon into the top exhaust which will go right down to the fan. I would just use a different piece of insulated ducting and lay it on the ground behind my washing machine. I don't have the option to exhaust outside so in the room it goes. Right now when you stand in my laundry room and put your ear close to the exhaust on the wall you just hear air swishing. Real quiet.


Member of the Month: May 2009, Oct 2010, Sept 2017
Silence is golden :thumb: . Thanks for the how-to writeup (and link to same ;) ) .


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Silence is golden :thumb: . Thanks for the how-to writeup (and link to same ;) ) .

Hah, no prob. Thanks for the 2 year bump.

I've been gone from here for awhile and a comeback is due. This fan and box has been extra quiet with zero issues. For shits and giggles I'll post a pic with my clone/seedling tent in place. As of right now I shall enjoy a bowl of Orange Creamsicle.

Mr. Krip

Grow Journalist
420 Staff
Nice work! :welldone:

I had done something similar back in 2010 when I built a stealth grow cabinet.

I also glued some foam to the insides of the box to help reduce the noise further. These are actually pics from my 2nd post here on :420:!




Here's a look at the full grow cabinet. I used it for many years and had to take it down a little over a year ago when I had to do some remodeling to the house. :rip:



And, the whole thing sat in this closet:





Well-Known Member
You're smarter than the average pickinick basket, you understand there's a concept called decoupling. At least you seem to from the rubber 'washers' you installed. Unless they're a special material, I don't think they balance the equation.

Let me put on the Mr. Whoopie hat. The goal is to cancel vibrations similar to how noise cancelling headphones work. Noise cancelling phones are to smart bombs as earplugs are to the gravity/crosswind (edit- should have added launch platform speed;)) steered variety.

With the phones, it matches pitch and intensity by emitting the opposite frequencies at the correct volume. Technical term's phase cancellation. What it all boils down to is I don't think you have the correct thickness/density of material to cover the range of variable's the vibrations of the fan are going to throw at it. Understand what I mean?

I plan on similar, but I have old rubber grommets from shock absorbers that will sandwich it at the mounting point with larger holes through the wood so there's no mechanical contact and then I'll hang the fan from springs to further 'decouple' it from the chassis.

Sounds overboard until you understand my greenhouse is in what once was my home recording studio which is piled in a corner. I've gone through great lengths to limit the things that can squawk while I'm recording so it doesn't add to the noise floor.

Stealth might not be as critical for you, but figured I'd put it out there for others. ;)
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