Fan Airflow Direction


Backer #263. Just received my EON today. As several others have posted, my fan was mounted with the airflow pointing down. I took the screws out to flip it and noticed that the mounting holes on each side of the fan are different sizes. This makes the fan sit more flush to the top of the case when it’s mounted as shipped. That is, if I flip it, it will be sitting slightly lower in the case.

I know that several backers have stated that the fan should be directing airflow up and based on my two Synology NAS units, I would tend to agree. However, before I flip it, can someone from Argon 40 confirm whether or not this is an assembly error? Which direction should airflow be directed…up or down?



I’m not affiliated with argon40, but I think it is either a design error or a manufacturing error.

There are vents on the top and bottom of the unit. The natural airflow without a fan would be warm air rises out the top of the unit and replacement air is pulled into the bottom. Fans work best when they augment or redirect the natural flow, not when the try to reverse it.


I also have a couple of the Argon V2 and Argon ONE m.2 cases with the built-in fans.

I just checked those, and they are set up so that air is blown out the top of the case by the GPIO cover.

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Sorry to hijack this post but I found the exhaust fan at top of unit to be less than useful for the pi board. Tests indicated that it does not function for the purpose of cooling the harddrives and it’s location is not ideal for helping the cooling of the Pi board.

So, I’m thinking of installing a micro fan under the inverted Pi board to blow a gentle wind across the board and heat sinks and tie it to the exhaust fan or convert the exhaust fan to support harddrive cooling fan based on OMV’s S.M.A.R.T sensing.


If you do this can you supply some pictures on the placement and connection.

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Thank you for all the feedback, we will give a definite answer on this concern after our technical team resume work after CNY break.

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I do agree with you somewhat (about the airflow and design), but is this type of answer/input really necessary? Not everyone comes to the same conclusions and sometimes things get installed the wrong way. I once ordered a photodiode board for a different project and the photodiode was soldered the wrong way. So in short, it can happen!


Sure, one-off mistakes are made all the time. But we aren’t talking about an inconsistency between delivered units… at least not based on the input we have seen thus far.

Yes, that is most likely true. But there is no need of shaming people or being mean. You could have used a different phrasing, that’s all.


A comment in another thread noticed that the prototype unit in ETA Prime’s Youtube video showed the fan pointed up. I myself was not able to get a good enough look at it.
This is the only instance I’ve heard of a unit having the fan pointed up.

Anytime you push air into a chamber, you either have to exhaust some air or a positive pressure builds. As positive pressure builds in the chamber, you will reach a pressure point where the fan blades can no longer overcome the pressure and no air moves. So to leave the chamber, the air has to be pushed through the same path you are complaining about, all while fighting the physics of heated air rising.

The bottom of the EON unit has vent holes that mirror those on the top. The PCBs will add turbulence to the air, but will not decrease the volume of air moved.

The most efficient way to cool a chassis is to allow the hot air to naturally rise and vent out the top. Warm air rising from the middle drives will still be exhausted and replacement air pulled from the bottom.

There are many people with 2 digit IQs that fail high school physics and don’t understand heat, pressure, and airflow.

Also, anyone can do a quick Google search and know that you are wrong.


The best situation would have been to have mounted a fan directly below the SATA board while having slots in the board to allow the airflow to actually do its job to cool the drives… but thats not what we have.


Most people do not have degrees in thermal dynamics or mechanical design. You should temper your comments accordingly, otherwise you just come across as arrogant (even if you have the technical experience).

There are ways to educate and inform with-out being borderline insulting.

In my non-expert opinion but using logic (and my 3-digit IQ :wink: ) It would seem more logical to pull hot air out from the top of a enclosed unit rather than push cool air in. By pushing cool air in you are ‘fighting’ against the flow of the hot air rising up … just my opinion.

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If you weren’t going out there to offend then people might be a little more warming to your advice. Just saying.

The fan blowing down only helps when the side panels are open. Objectively speaking with all the side panels in place, there is 4C drop in temperature under heavy load for an extended period with the fan pointing up in my testing vs fan pointing down

The drop in temperature aligns with “hot air goes up” logic. With the fan pointing down, most of the warm air only circulates inside. If that 4C difference matters to you, you’d probably want the fan pointing up. Otherwise, you can keep it pointing down.

Also to note, under short burst loads, the orientation of the fan does not matter. It may not even turn on if you have it set to turn on at default 55C. Passive cooling will work well enough. The idle temprature of my setup is just hovering under 40C at ambient 24C.

So, there you go. If you are really worried about the drives heating up, you may want to figure out how to let in more air by making the side panels let in more air… drill holes maybe? 3D printed spacers to open a gap? Up to you.


Good to see some empirical evidence.

That’s a good point. The passive cooling of the EON is impressive. I had sysbench running all cores at 100% for quite a while. It was difficult to get the temp over 40C never mind 55C. As soon as sysbench stopped the temperatures dropped very quickly.

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I saw a temperature of 42 C yesterday when I deliberately broke the raid and rebuilt it and the disks were syncing/rebuilding.
Agree that the passive cooling is good, the fan has only worked prior to installation of script. My system is currently showing a temperature of 36.5 C (97.71 F) the aluminium case is slightly warmer to the touch at the bottom and there is warmish air coming from the top vent.

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Can we get an official answer from Argon 40 on this topic?


After some testing, we do agree with most of the observation here in the forum. Moving forward, we will invert all the fan in future shipments.

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Can you make a recommendation to existing owners of how we should proceed? The reason I ask is that just flipping the existing fan makes it a tight squeeze to install two 3.5 inch drives.