With respect to my other question here, I have attached an egg box over the exhaust fan on my PC that was making a noise. The image does not show it clearly, but there is a ~1.5" clearance between the PSU exhaust and the egg box as per my annotation. I can feel the air coming from the top of the egg box, and from the small hole in the box (indicated), showing that there is still "exhaust" coming out.


Is this method of redirecting the air safe so that it will prevent overheating?

Update: this question is different to that linked above, because this question does not completely block the PSU exhaust, it - for want of a better phrase - shields it but still allows air flow.

  • I like your solution for when I have a PC backed up in a cabinet and can't get the fan to blow with any room; however, I have yet (in 30 years of doing this) to see a power supply whine because of the coil. I have (many times) seen them whine because of the fan itself inside of the PSU. As far as your specific question, try it and watch your internal temps closely. I personally think this isn't a good idea. Aug 20, 2021 at 16:38
  • What sort of noise is coming from the computer? Is it a screeching, a noise like a vacuum cleaner, a high-pitched whine, or something else? Maybe you could record it and upload it somewhere for us to listen to, so that we can figure out what the cause of the noise is. Aug 20, 2021 at 17:25
  • Is there anywhere for air to enter at the front of the case, not just round the sides from the back? Does the case have any dust filters that might need to be cleaned? Aug 20, 2021 at 17:27
  • Thanks both. I"ll monitor the temps. The noise is like a vacuum cleaner, but softer. It's not the fan, as I've watched the fan as I turn PC off and noise stops immediately whereas fan continues for a few seconds. There is plenty of space from the front, and I've compressed-air cleaned all fans so they are spotless...
    – Wad
    Aug 20, 2021 at 17:39
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    No it does not. That (my) previous question asked about completely blocking the PSU exhaust. This question is asking about what I have done instead, which is shielding it on left/right/bottom, thus still allowing air flow, and whether that is safe.
    – Wad
    Aug 20, 2021 at 18:54

2 Answers 2


Seems reasonable, especially if your PSU is has a temp-controlled fan that will spin faster as its own temp increases, and/or the components in your PC won't come close to the PSU's max rated load. (e.g. a 400W power supply with a normal non-overclocked CPU rated for a max of 80 or 110W, and no separate graphics card or a moderate one.)

If you almost never run your computer at high load / high power draw (e.g. gaming, video encoding, number crunching) for a long time, you mostly only have to worry about near-idle power draw. Modern desktop PCs may idle at about 15 to 20 W total, but mobo+CPU+SSD full power can be up towards 150 W even for a "consumer" quad-core chip, and beefy GPUs can consume hundreds of Watts on top of that. So make sure you check temps under load unless you only ever do short bursts of load, like compressing a medium-sized file, or compiling for a minute or two. (It takes time for the thermal mass of everything to heat up).

Hearing the PSU fan spool up will be a clue you might be pushing it, temperature-wise, if your PSU fan is temperature-controlled.

Also, I assume you have a separate rear exhaust fan in your case to ensure good airflow over the CPU heat sink and other motherboard components like RAM and voltage regulators, and hard drives / SSDs. Fortunately you can usually monitor temps for many of those components via sensors in the CPU / motherboard, and SMART for hard drives / NVMe, so definitely do that to see how much difference it makes at idle and load.

The more heat the PSU has to get rid of to keep itself cool, the less good an idea this is. E.g. if had a 1000W PSU and actually used a significant fraction of that capacity with some dual GPU setup, at 500W output load with a PSU that's 80% efficient at that load level, you'd be creating 100W of heat inside the PSU box itself and would need some serious airflow to keep temperatures down.

(Check the vendor's specs for temp range, and leave some headroom for dust buildup and hotter days in the future if you have a way of monitoring the PSU temp at all.)

One concern would be if the exhaust air gets deflected forward (instead of out away from the case) and mixes with air that gets pulled in to the front intakes, raising the effective ambient temperature. Your setup (under a desk) might mitigate that some, and there's lots of room air to mix with. (Especially if you have some air movement in the room).

Hot air rises, so that should help it stay away when you just deflect it mostly upwards.

Feeling the exhaust air by hand is a good check for PSU temp, maybe also touching the back grille. Make sure you do this with the PC under high load, preferably higher load than you would normally impose so you have a worst-case idea with some headroom.

  • Thanks Peter. I don't think there is a second exhaust fan; the only two fans are the one attached to the PSU, and an upright standing one which seems to blow air onto the board. I've got some software which monitors the components in the machine, but the PSU itself is not one which supplies temperature data. I also regularly "feel" the air coming from my makeshift exhaust pipe, and it is surprisingly cool; but the real test will be when I put it under load.
    – Wad
    Aug 21, 2021 at 15:09
  • @Wad: So your PSU has 2 fans built-in? And there is a fan separate from the PSU, but it's at the front of the case, as an intake fan? That might be ok, and will likely result in some air movement over the mobo out the back exhaust port (with the PSU fans still pulling some through the PSU itself). Aug 21, 2021 at 15:11
  • @Wad: feeling the temp of air coming through your exhaust duct is a good idea. If there's good air movement and it doesn't feel hot even before it can mix much with room air, that's a good sign. Your duct is adding a bit of extra resistance for the fans to push air past, but if they have enough pushing capacity to overcome a bit of back pressure you should still be fine. Aug 21, 2021 at 15:14
  • Another concern with your duct would be where the hot air ends up. If the computer sucks in more of it than it would otherwise, that means the effective ambient temp is higher. Aug 21, 2021 at 15:16
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    @Wad: "it can't bounce off" - fluid dynamics and turbulence are really complicated. I'd guess that some would end up deflecting forward, moreso than with air going straight out the back (even if that's toward a wall), since straight away from the case would put it farther away from the intakes as it rises and spread out as it mixes with the room air. It's probably a minor effect, especially if the fans aren't cranking hard. Aug 21, 2021 at 15:32

Typically, the manufacturer of the PC will have a data sheet that specifies airflow, temperature, humidity, clearance, and similar requirements. The simple answer is: if you satisfy those requirements, this is safe, if you don't, then it isn't.

If you built the PC yourself, then, well, you are in some sense the manufacturer, and it is your responsibility to comply with all the individual data sheets of all the individual components (case, PSU, motherboard, CPU, GPU, RAM, storage, etc.). And again, if you satisfy them all, then this is safe, if you don't, then it isn't.

Note that there may be different kinds of data sheets for different audiences. Since we are concerned about things like airflow and temperature here, you might not find the necessary information in the normal "user" data sheets, but might have to look into e.g. data sheets intended for OEMs or system integrators.

Just as example: for most of the devices with front-to-back airflow that my employer manufactures, this would not be allowed, since it violates the clearance requirements.

  • Thanks Jörg. I didn't build the machine myself; moreover the PC shop owner didn't ask me where I intend to put the machine, or otherwise ask questions that would facilitate gaining information on whether or not there would be adequate flow. I think my best bet is to monitor the temperature of air coming from my egg box; if it feels hot, then I need to make changes.
    – Wad
    Aug 21, 2021 at 15:13

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