Is Passive CPU Cooling Best for Silent Computing?

In a word, NO.

1. What is Passive CPU Cooling? Passive cooling means cooling without any forced airflow. In PC circles, the meaning has been watered down to cooling without an active fan directly on the heatsink. In reality, a fanless heatsink that is within an inch or two of an active case fan does not constitute fanless cooling.

2. Does the CPU HS fan only cool the CPU? The fan on a CPU heatsink has the task of cooling not only the CPU but also important components on the motherboard such as the NorthBridge chip and the Voltage Regulator Module (VRM) which powers the CPU and sometimes other components as well. Motherboard manufacturers assume a certain amount of airflow from the CPU HS fan in their thermal design. Eliminating the CPU fan -- even with a massive, low-airflow-optimized heatsink -- usually means that those motherboard components will run a lot hotter. This can lead to instability and shorten the motherboard's liefspan. The usual solution is to increase the airflow from case fans, which then increases the noise -- which then negates the whole point of running the CPU HS w/o a fan.

3. Isn't eliminating another fan always quieter? No. It has been shown time and time again that multiple fans can be run at very low speed quieter than 1 or 2 fans spinning faster to push the same amount of air. Multiple fans have the benefit of more focused cooling airflow to areas that really benefit, and a degree of fail-safe functionality -- ie, if one fan fails, it is not critical as there is still airflow from other fans helping out. The other issue is whether there are other noise sources in the PC that will make eliminating the CPU HS fan worthwhile; ie, there may be no audible improvement anyway because other components make as much or more noise. Finally, a small amount of airflow from a good fan is usually as inaudible as no fan at all, yet the temperature improvement can be well over 10C or even 20C.

Fanless cooling of high density thermal points such as CPUs or GPUs is only worthwhile when...

1. Doing so really reduces the noise audibly.
2. Cooling of other important components in the system is assured by other means (for example, with heatpipes in a "heatsink skin case")
3. The CPU or GPU is kept within safe operating temperatures even in a worst case scenario.

I've been slowly coming to a similar conclusion myself. And I think they way you say it says it all... at least when it comes to air driven cooling (resonance and mechanical hard drive noise I think are a different subject.).

1. Just a little air motion makes a big big difference. Why forgo it?
2. The CPU isn't the only thing that needs cooling.
3. If you want the most cooling with the least air movement, put the fan near what you are cooling.
4. All things equal, two slower fans can move the same amount of air with less noise than one faster fan.
5. If you really have a quiet computer you might not notice a dead fan right away, why forgo the safety of a redundant second fan... for what benefit?

Corollary1: As hot rod coolers go, downdraft CPU coolers aren't always the best performers... but they are the most balanced... cooling parts that are not cooled by "higher performance" tower coolers.

Corollary 2: How much noise, really, does a good fan make turning at 500 - 800 rpm. How much more noise, really, will a second one make?

Corollary 3:
Option 1: If your computer can get by with no fans... good for you.
Option 2: Otherwise there is nothing wrong with two slow fans gently changing the air over heat radiating surfaces.
Option 3: One fan on a system that will overheat if that one fan fails, is the least wise of these three options.


Mike, did I miss anything.

There are a few minor reasons to forego fans, one of which is cost.

The question is, what are "safe operating temperatures" as MikeC says? If you go by the manufacturers' maximum temperatures, there's a lot of stuff which can be run without any fans. But what would be the impact of high temperatures on the components' lifetime?

If you can go without fans and maintain temps that are acceptable to you - go for it. If the temps are too high... cheaping out on a $10.00 fan is false economy.

Yeah... what are temps that are too high? Certainly temps above manufacturers' maximum temperatures are likely too high. Most people, myself included, don't even know what those temps are.

The flip side of that question is what temperatures are safe? My personal rule is that if it is a temp that a human being an tolerate, that is a safe temp for silicon, copper and steel. 45C / 113F, how can those temperatures not be safe? Another 5C.... I'm still OK with that. 55C / 131F, I am starting to get concerned that I need to know what the manufacturers' maximum recommended temperature is. If I have to know what the manufacturers' maximum recommended temperature is, then I am not comfortable.

Where did I get this from. I just made it up.. but it feels right to me. There is no magic temperature or magic voltage above which a chip suddenly burns up. So it is hard to determine the criteria that different manufacturers use to set their recommended temperature. One manufacturer may use one set of criteria for determining max recommended temps and another may use another set of criteria. If it is an attribute that affects sales, marketing probably gets a vote on setting that number.

Here is an example: Gigabyte claims its capacitors are rated for 50,000 hrs 85°C ambient temperature. What does that mean. Does that mean on average... that is 50 percent fail before and 50 percent fail after? They don't say. What percent of degradation occurs before failure. What does that failure envelope look like... sudden or gradual? And what impact does a working capacitor functioning at a diminished capacity have on other components? Who knows.

All you can know for certain that every increment of heat, and every increment of voltage, is going to diminish (not increase) the life expectancy (and likely other performance attributes) of any electronics. Though strangely Google's data for their hard drives which are running pretty much non-stop, is that too cool or too hot diminishes expected lifetime performance of their hard drives (though too my knowledge no one knows why this was so).

Can you run it hotter than my crude personal guideline. Sure. I am probably being overly cautious. But that caution isn't likely to be the cause of the early, untimely (and inconvenient) failure of a motherboard or other electronic component.

Is complete absolute silence worth the risk of diminished component life, which risk may or may not even exist? That is a personal decision. No moving parts is very appealing. But two sliptreams running at 500-800 rpms how loud are they really? How expensive are they really? (don't forget as the speed of the airstream slows, static pressure becomes less and less of an issue).

First, the cost of a fan or 2 is trivial in the context of a PC.

Second, this is not a scientific poll but --- as a result of my work over the past decade, I have seen dozens of aged PCs. Once a PC (or motherboard) gets more than a couple yrs old, the failure rate seems to start rising, whether cooled very well, moderately, or without fans. I can say w/o hesitation that there is a direct correlation between higher failure rates and lower airflow. This is not to say that if you run your computer with minimal airflow/noise, it will fail sooner... but the risk of it happening is higher than in a more conventionally cooled system.

The parts I have seen fail most often in super low airflow systems: PSUs & motherboard, followed much farther behind by video cards... tho keep mind that most quiet systems have not run very hot GPUs.

What a multiple slow fans configuration has over a 0/1 fan setup is that the latter can ensure some airflow over all the hot components in a system while the latter cannot.

MikeC, would you be able to quantify your impressions with regards to temperatures and component failures?
I think that would be valuable because very few people have as much experience as you do about how mainstream desktop gear copes with low airflow.


Not necessarily.
You mention Slipstreams. Ordering one would cost me $15-25, not $10. And that's not the total cost of course. For an expensive system, that's not an issue. But for a cheap system...

I'm sorry Mike but there's no maningful "context of a PC" anymore. edit: The developement of the smartphone/tablet/netbook market and the energy shock means that the reckless spec inflation era is over. Devices with very different prices and abilities are going to coexist.
There's always been a second-hand market but new low-end parts have never been that cheap and even the second-hand stuff is more useful now than ever. Relative costs and changes in pricing are probably different from your perspective in North America.


Thank you for your honesty. What we'd need to make rational decisions is data about component failures.


As you may know, some manufacturers sell fully-built systems which get a good bit hotter under normal use (as opposed to benchmarking and the like).
But, for all I know, heat tolerance might vary drastically between components. Mobile and desktop gear tends to have different maximum temperatures according to the manufacturers for instance.

Except when you consider the added cost for going 100% fanless. A proper enclosure with huge heatsinks on everything will set you back more than a simple enclosure with cheap heatsink+fan combos that can be run at inaudible noise levels.

Mike, Could you clarify that more words. I thought you were saying that your experience is that better cooling, within limits, does in fact reduce the failure rate?

@Modo: you don't necessarily need huge heatsinks for fanless operation. You only need sophisticated cases if size is a concern. And even that's not a given. Cooling requirements vary drastically from one market and architecture to the next nowadays.

The main issue is not whether one should use fans or not. Fans aren't always needed but they have their place.
The information you need to determine rationally whether it makes sense not to use fans is also needed to determine what fans and fanned heatsinks you need.
People tend to use too many fans running too fast above heatsinks which are too large. It's wasteful but what else can you do when you don't know how hot is safe? And if I'm wrong about how conservative people are it's just as bad: lots components would be failing because they get too hot. This lack of information is hurting everyone.

It's true that the requirements scale down, but the difference in price between a big heatsink vs a small one plus fan remains. Note how even the tiniest computers often have fans. Heck, look at laptops. If it wasn't expensive to go fanless, everybody would do it to improve reliability by getting rid of moving parts.

The economics are different for manufacturers and consumers.
There are manufacturers which go for fanless and their products are not always more expensive. Again, fanless heatsinks don't have to be huge or expensive. It depends on how much cooling is needed.
For a consumer, it works like that: stock fans and stock heatsinks are free while small specialty parts are overpriced. While stock heatsinks of course make no noise, I have yet to stumble on a quiet stock fan. There probably are some very quiet if not silent stock fans on the market but so far as I know they're not common yet.

Would you care to name examples? Preferably of PCs suitable for gaming.

Name one.

I beg to differ. If we're talking PCs, they are ALWAYS more expensive than fan-cooled, often by a big margin. This has been true for as long as I have been watching (over a decade).

As for what are "safe temps" -- this is not a good question, it is far too general. What I said -- and will say again -- is that when no fans are installed in a PC, components run much hotter than when fans are used (even super slow fans), and component life generally is shorter.

This holds true for not only DIY systems but also custom-designed fanless systems factory-made by the likes of Mappit, Hush, etc. Motherboard selection becomes very important for fanless systems -- capacitors rated for higher than normal temps (105C, etc) are a minimum, to me. (For example, there were some Hush/Niveus systems which featured FIC boards years ago. I personally know of several system with these boards that died early -- mostly because mobo components failed, and also because of PSU failure.)

And to ces: Yes, better cooling, within limits, does reduce the failure rate.

One way you could describe the difference between very low airflow systems (which is mostly what SPCR encourages) and fanless systems is that the former can be set up to provide adequate cooling even at extreme conditions, while the latter can easily slip into inadequate cooling in extreme conditions.

What are extreme conditions in normal use?

Heavy CPU/GPU load (like gaming, video encoding, etc) combined with hot weather. 30C weather is not that unusual for a month or two in a year even in temperate zones. Now, one hot summer hopefully will not kill a passively cooled system, but repeated excursions (even if short) into too-hot temps over several years -- this is what causes the damage. Think of pro athletes' injuries. Often, it's not a single big hit or injury that does the damage -- it's what exposes the long wear and tear the body part has taken over many years.

I am not espousing the kind of paranoia about temps you see in many first time posters here (and in umpteen other sites)... worry if CPU/GPU temp exceeds 60/85C after an hour of prime95/furmark. Those are extreme lab tests that substantially exceed the loads of any normal apps, and should always be considered worst-case scenarios. What I am saying is that once you have achieved a level of noise that makes the PC a non-factor in your acoustic environment, there is NO benefit (and there is possibly a real cost) to removing or slowing fans any more. Conversely, there IS often a benefit to increasing fan speed or # of fans if it can be done without increasing audible noise.

Mike, would you be kind enough to express an opinion as to whether the configuration I propose here:
viewtopic.php?f=8&t=61324&p=531249#p531249
likely might pass that test?

.... well it probably won't... but do you think it might stand a chance at coming close? I know the only way to tell for sure is to do it... but you've seen enough that your intuition is not likely to be that far off.

And if you don't engage in gaming or other heavy duty multiple thread uses, is the CPU/GPU temperature generated by a prime95/furmark burn always that important of a temperature benchmark?

For many people, a 2600K even when pushed hard, won't even be breathing hard. The highest temp it ever reaches will be much lower than what is generated by prime95/furmark burn.

Maybe a suitable alternative benchmark might be to run CPUID HWMonitor nonstop for one month and see what the highest max temp is that it registers over that period of time. For many people this temp would be substantially less than the temp generated by a prime95/furmark burn.

What do you think... especially about my proposed configuration?

An aside on capacitor reliability...

Capacitor reliability has 7 or 8 variables. The capacitor build and chemistry, it's rated voltage and the max voltage it sees, it's rated temp and temp you use it at, the operating environment, etc..

If you want to have fun with capacitor lifetime calculations, here's a calculator @ Vishay for tantalums.

Does the lifetime improve with lowering temps? Yes. How much improvement you get sorta depends on how close to the edge of the component specs your system is running. Here's a sample curve using the calculator. This is a 10V 0.1uF cap rated for 125C operation, benign use, fairly low circuit resistance, and seeing 5V max.


The MTBF at 125C is 3.46 Million hours. You've got to drop the operating temp by 55 degrees to 70C to double the MTBF. To double again, drop the temp by 25 degrees to ~30C.

Take that same capacitor and raise the app voltage from 5V to 6V and you half the lifetime. Kick it up to 7V and you reduce the MTBF by a factor of 10.
................

Aluminum electrolytics have a much steeper temp curve, and you might see a doubling of MTBF every 10-15 degrees..
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I'm note sure what you're asking me to name since you've reviewed several fanless products. But since you go on to talk about fanless PCs, would Shuttle count? Their cheapest fanless model is about $10 cheaper than their cheapest fanned model (local prices).
Times are changing. If you go back a bit more than a decade, fanless heatsinks paired with cases with dreadful airflow were the norm. The Mhz war culminating in the P4 changed that. And now the trend has reversed and we're starting to see fanless heatsinks again.


You're the one who brought up "safe operating temperatures". I agree it's too general (just like your statement above) but it gets the point across.
We'd need to know *how much* component life is shortened in order to go beyond general statements and to make good decisions about the costs and benefits of fans.

Arguing that fans have no costs is hopelessly wrongheaded. Removing a fan has a tangible benefit which everyone can weigh for themselves (sometimes it is negligible). And the costs involved in adding a fan are likewise tangible.
But the benefit of fans for systems which can run without them is not tangible. That does not mean the benefit is not real but that means that, until it is quantified, for all we know it's insignificant. As the Google study on hard drive reliability referenced above has shown, what most everyone believes to be significant sometimes turns out not to be.

It makes little sense to test your cooling with furmark if you're not going to use the 3D features. Someone correct me please if you know a scenario in which the GPU is accidentally heated up.
But it does make sense to stress the CPU because lots of things like buggy programs or user errors can accidentally give the CPU heavy multi-threaded work. If you don't intend to give it such work, underclocking the CPU may (or may not) allow you to tweak the cooling safely. But I would always stress-test the CPU to see if the tweak is safe.

In my personal opinion, I don't think the Shuttle counts. Do you have any other examples? (you can always admit that maybe you got a bit carried away and perhaps exaggerated a bit... we've all done that here at one time or another)

For some posters, it's the argument that matters, not the subject....

When all is said and done, I don't care whether people want to disagree or agree with my comments here. Remember the header of this thread:

Is Passive CPU Cooling Best for Silent Computing?

The reason for my original post is simple: To answer the umpteen folks who come to these forums over the years asking, "Can this CPU be run fanlessly with that heatsink?"

In a nutshell, my answer is -- Why bother trying when there is no benefit over a nicely optimized low airflow fan cooled setup that will sound every bit as quiet and most likely run more stable for a longer time?

The low airflow, multiple fan approach simply works for silent computing -- generally better than fanless. Puget Computers' last couple Serenity SPCR Edition builds are a testament to this fact.

This is a pretty open forum & you are all free to advise such folks as you see fit (within reason). This is how I am advising them.

No, that doesn't count. It's an Atom system.

Reading your comments, your philosophy is to buy a system capable of running fanless. That's nice for you, but that's not what Mike had in mind when he started this thread. If you're happy with an iPad, go for it. But the people who come to SPCR usually need a PC for specific reasons: 3D workstation, Audio workstation, Gaming, etc.
An Atom, VIA Nano or ARM Cortex won't cut it here. And it's not like they are available in retail anyway. They will come at the very least with a mainboard and a cooling solution. It that's passive, so be it.

But this threat is about DIY computers. And if you spec your PC to your needs and not the other way around, most SPCR readers can't get around either an Intel Core something or an AMD Athlon/Phenom.
Getting these system fully passive, especially with a Gaming/Professional Grade GPU, is possible, but very tricky. In this context - that's what Mike meant - getting 3-4 Slipstream fans (8$ in Germany, don't know about Switzerland) is economically benign, will not elevate the noisefloor unless you're working in very specific environments, will improve in-case climate dramatically, insures against worst case scenarios and widens your choices (as there is no way to cool anything like a GTX580 passively).

+1

By definition a silent pc would have to be passively cooled.

The G4 cube came closes. When SSD becomes affordable and can replace HD's, I think a purely silent pc will be possible.

No. The universe is never quiet. But most of its sounds are thankfully inaudible to us. By definition, a silent PC is one that is inaudible to whomever it concerns.

If you can't hear a couple of slow spinning fans and they help cooling, then there's no reason to do away with them. That's the point of this thread.

If you do hear any moving fan, no matter how quiet, then yes, a passive setup could be the solution. Or moving the PC out of earshot.

in my bedroom during winter, i can use speedfan to disable the 2 scythe ninja fans so they are NOT spinning. the HD is a bit "loud", 7200rpm seagate FDB. The corsair vx450 PSU fan i can hear. I can "disable" it by sticking a chopstick to stop the fan from rotating and I can manually unplug the HD, and run off the SSD.

My pc is then totally silent.

This statement tells me that...

1) you are thinking of sound only as a physical phenomenon, the generation of vibration transmitted through the air. There is another definition of sound, which is the perception of said phenomenon. ie -- if no one is there to hear it, is there sound?

2) you have never "heard" a truly quiet fan-cooled system. I have... and can say honestly that they can be so quiet as to be no different (in subjective perception) from PCs that have no moving parts. (I have some of the latter, too.)

+1

Just to remind people that it is possible to make a custom bracket to mount a fan that points at the motherboard and still run a passive CPU cooler. Though, it has to be a huge thing with a Celeron or similar to get away with it. 500-700rpm is enough airflow. Often most of the CPU fan noise is the back-pressure from the air flowing through those little fins, which are almost always too closely spaced. A fan pointing at the board itself, tough, will have nearly none and run quite a bit quieter.


You have seen this all the time, from gaming consoles like the PS1/2, printers, stereo receivers, TVs and so on. 120-130F is pretty safe and can be run that way for years or sometimes decades. Anything over that and you're shortening the life. Though, since most people don't keep their PCs for 15-20 years, it's not a huge problem. But a passive only design can top 160-180F easily and poses unique challenges in the design and the components (Just ask Apple and note how many failures they've had in the past trying to get it right). Most PCs (motherboards especially) are not designed with special heat-resistant components and are designed around the assumption that fans will be used.

That's a fair point that other components on the motherboard will run at higher temperatures. Most reviews only look at the temperatures of the CPU when reviewing a cooler. Shame there isn't any data available for other temperatures. However passive coolers are designed to run effectively without a fan so if you attached a low speed fan to the heatsink you effectively have a conventional cooler that runs a lot quieter. That's the plan anyway. Just checking compatibility for the cooler i want and then i'm gonna combine it with an Enermax PWM fan with a manufacturer rating of as little as 8dBA. As the heatsink will be greatly reducing the heat of the CPU alone, the fan will only run at a low power and everything will still be kept cool at a low noise level.

Which Enermax PWM fan?