A high efficiency fanless PSU is a great starting point for an ultra quiet yet powerful modern PC. In our latest system build guide, we explore case and configuration options, share our observations about how a fanless PSU changes PC airflow, and walk you through the fine details of a full fledged PC build with a fanless Seasonic X series PSU.
October 8, 2011 by Lawrence Lee and Mike Chin
Fanless ATX PSU options have never been plentiful. Many of the models that came and went in the past decade couldn’t deliver their rated output, made nasty electronic noises, and/or overheated and shut down when asked to deliver substantial loads. Suitable only for low power systems, yet priced prohibitively high, it’s easy to see why they never succeeded in growing much beyond a little niche. Our Fanless PSU Torture Test Roundup a year ago showed that there are still very few fanless PSUs worth considering.
On the positive side, three modern fanless PSU models have emerged that we can recommend without hesitation: The Seasonic X-400 and X-460, and the recently reviewed Kingwin Stryker STR-500. All are extremely efficient, with 80 Plus Gold or Platinum ratings, hold up well thermally and electrically under high load, and are as silent as can be. Current pricing for these units is also excellent with Newegg offering the X-400 and X-460 for US$90 and US$110 respectively (after mail-in rebate). The STR-500 is a bit pricier at US$160, but it’s a small price to pay for the most efficient, silent, passively cooled PSU on the market.
The Seasonic X-400, X-460 and the Kingwin STR-500 are the best fanless ATX PSUs in the market.
Without a fan to blow over its internal components, a fanless power supply needs to generate as little heat as possible, employ large heatsinks to dissipate the heat it does generate, and be well-ventilated. Even the most efficient power supply will falter if you stuff it into a closed system. The passively cooled PSUs we mentioned above all have a very open physical design, with mesh-like panels to maximize of air flow and ventilation. Most cases are designed for power supplies with internal fans, however, and many DIY builders wonder how a fanless PSU fits in thermally in a PC system.
Given the availability of these high tech, super-efficient, fanless power supply marvels, we’ve put together an article to address the question of how to get the best use out of them. We have been working with fanless PSUs for years, and we have some useful tricks and observations to share with you. We consider typical case layouts, the airflow that is normal in such cases, and discuss how a fanless PSU affects the cooling and airflow. We will also do a step-by-step build of a fanless PSU system as a guide for the uninitiated builder, ending with a complete thermal/acoustic analysis of the system.
"TYPICAL" ATX TOWER AIRFLOW
The original ATX tower design that dominated for the last two decades is based on a front-to-back airflow concept. There are variations, for sure, but in general, a fan or two on the front panel draws in air and blows it across hard drives, and into the center where the hottest components are. There’s almost always an exhaust fan on the back panel next to the motherboard I/O panel, and a rectangular hole on the back panel for the PSU. That hole is for the PSU air exhaust, and the original ATX design places the PSU at the top back corner of the case. An inherent aspect of this arrangement is that the PSU ends up directly over the CPU, and just a few inches above the VGA card as well, and as a result, the PSU fan sucks in much of the heat from those components into its casing. This causes unnecessary heating of PSU components, and the extra heat often forces the thermally-controlled fan in the PSU to spin up, resulting in higher noise.
Old school ATX tower (example: Cooler Master Sileo 500) with top/back PSU mounting location.
BOTTOM MOUNT PSU ATX CASE AIRFLOW
A modern ATX case variation puts the power supply at the bottom, out of the heat path of the CPU. When combined with a bottom intake vent for the PSU, this design keeps the heat of the CPU and GPU apart from the PSU, which now only has keep itself cool. This design divides up the heat to separate exhaust paths so that it is more easily managed.
Modern ATX tower (example: Cooler Master Silencio 550) with bottom PSU position and bottom panel intake vent.
In bottom PSU cases where there is no bottom vent, the PSU fan draws in air from inside the case. This can work fine except when more than one VGA card is used. Then, the second or third vidoe card can end up being very close to the PSU fan, with the same type of thermal jam-up that can occur in top-PSU cases.
FANLESS PSU IN THE ATX CASE
The defining quality of a fanless PSU is its fanlessness. Obvious, but thermally, what does this mean? A fanless PSU is a source of heat, though the three we consider best produce very little heat. They are also very well ventilated. Combine the existing PSU exhaust vent in the case with the openness of these fanless PSUs, and what you end up with is… a vent. Basically, from an airflow point of view, the fanless Seasonic or Kingwin PSU is a somewhat restricted vent in the case.
So what is the function of a vent in a PC case? It allows air to flow in or out. Which way the air flows depends on the location, direction and intensity of other fans in the case. Of course, if there are no other fans, then natural convection and rising heat have their way, but for the time being, we’re only considering system with some forced air cooling.
Let’s consider what happens in an old school ATX tower case like the Cooler Master Sileo 500 pictured on the previous page. When a fan is spinning, air is displaced from one side of the fan to the other. The displaced air is continuously replaced by air flowing from elsewhere, and this flow always follows the path of least resistance. When that back panel fan is spinning without a PSU mounted in place, air flows into the case (and to the intake side of the fan) via the back panel hole for the PSU — this is the closest hole with the least amount of resistance. Mount a fanless Seasonic X there, and the outside air now flows through the PSU to the back panel exhaust fan.
Got that? The PSU itself becomes an intake vent for the back panel exhaust fan!
This phenomenon is easily tested by holding a strip of tissue paper at the exhaust vent side of the PSU. If the back panel exhaust fan is blowing out, the air flowing in will force the tissue paper against the PSU vent. This is not to suggest that the Seasonic fanless PSU becomes the only intake vent but one of many, unless all other vents in the case are closed off. However, its close proximity and the openness of the back and side panels of the Seasonic certainly makes it a prime intake vent.
Having said that, does reversing the flow direction of the back panel fan force air out through the PSU? Here, the answer is generally not as clear, because the airflow pattern on the exhaust side of a fan is usually more directed and focused than on the intake side. If you develop a positive pressure flow by making all fans mounted on the case panels blow inwards, then for sure, the PSU will become one of the exhaust vents. This will have some effect on CPU and GPU cooling, which needs to be checked empirically.
Empirical testing, by the way, is fundamental for thorough PC cooling setup, especially if you have not ventured into the balancing game of silent cooling. It means experimenting systematically before finalizing the hardware settings, including fan positions, speeds and directions.
FANLESS PSU IN THE BOTTOM POSITION
What happens to airflow when one of these fanlesss PSUs is mounted at the bottom/back of the case? Well, unless there is a fan fairly nearby creating some kind of forced airflow, convection rules. This is something you need to keep in mind: A fan’s cooling airflow "reach" is limited in distance, especially when run at the very slow speeds which make them silent (typically, under 800 RPM).
Anyone who takes delivery of a Seasonic X-series fanless PSU will see the big warning about mounting the PSU in the case with its vented top facing up.
Seasonic recommends mouting the PSU with its ventilated top facing up in order to allow convection to help with cooling.
If you have ever examined the interior of a standard ATX PSU, you know that the normal "up" position puts the PCB on the top, with all the components hanging upside down off it. A 120mm fan is mounted on the "underside" of the PSU, blowing into the PSU, and the air makes a 90 degree turn to exit out the back. So Seasonic’s mounting recommendation for its X-400 and X-460 is the reverse of the norm, in order to use rising heat of convection to help cool the PSU.
But as we’ve just explained, a single back panel exhaust fan in the case reverses the airflow through the PSU. The rising heat effect of convection in a typical computer is easily dismissed by the forced airflow from any nearby case fan. [Note: We could get hung up in a major defense of this point, but for now, take our word for it. We’ve played with things like this for a decade, and we are completely convinced that the airflow from any 80mm or larger diameter fan at even minimal speed provides many, many times greater cooling effect than convection in any PC using typical heatsinks.]
Let’s look again at the Coolermaster Silencio 550, which has a bottom PSU mounting position with an intake ven driectly below the PSU.
Coolermaster Silencio 550 more or less leaves the PSU to cool itself. For a fanless PSU, this could spell trouble under high load.
Neither the back panel exhaust fan nor the front panel fan are in close proximity to the PSU, so they will not impact the PSU’s internal cooling much, unless the fans are set to high speed, which is anathema to a silent PC. If the front fan was positioned lower, and nothing put in front of it to impede airflow, its flow might help the PSU a little. But even so, with the X-400/460 mounted facing up as recommended by Seasonic, the most likely scenario is that the hot air from the PSU would rise up, with a bit of the heat going out the back vent of the PSU, and more of it going up towards the CPU/GPU area, and be evacuated by the top back panel case fan. This is not a bad scenario, but it does increase the thermal load on the main CPU/GPU cooling system. Our torture testing showed that the Seasonic X-400/460 can withstand very high loads and temperatures without skipping a beat, so perhaps that’s the only real downside.
Flipping the Seasonic PSU would allow some outside air to get into the PSU via the bottom vent of the case, but this might trap some pockets of hot air in the PSU, which is possibly what Seasonic is trying to avoid with its strong recommendation about keeping the vented top up. In any case, you can see that the bottom PSU position does not actually offer any clear thermal advantages for a generously vented fanless PSU.
IN A 90 DEGREE ROTATED CASE?
The SilverStone cases with rotated motherboard trays, the Raven RV01/02 and Fortress FT02 seem suitable for use with a fanless PSU. As the GPU, CPU, and PSU are positioned horizontally to one another, the heat generated from each component radiates upward, having a minimal effect on adjacent parts. In addition, natural convection is helped along by three 18 cm intake fans on the case floor and a 12 cm exhaust on top. With the open vent top of the Seasonic X-400/460 facing the back panel vent, the air could flow through the PSU easily, cooling its internal components, and blow out both the top and the back. However, these large cases are tailored for high-end gaming systems which are inherently louder. It might be a bit wasteful to pair a passively cooled power supply with such a system, and the 400~500W rating of these fanless PSUs might not be adequate.
SilverStone Fortress FT02.
MODIFIED STANDARD ATX TOWER
The new Antec Solo II is a conventional ATX tower with one significant tweak: A large top panel vent directly over the PSU. As far as we know, it is the only ATX mid-tower case with a standard PSU position to offer this feature. The open face of the power supply is intended to face the top panel vent. If a fan cooled PSU is used, that vent is an intake from drawing in air from outside the case. If a fanless PSU is used, then top vent can be an exhaust or an intake, depending on how other fans in the case are deployed. Regardless, the extra vent is a benefit for cooling a fanless PSU, more obviously useful than the bottom panel vent in a bottom PSU case.
Any PSU in the Solo II is still subject to the hot air flowing upwards from the CPU and GPU, but the PSU panel facing the bottom is sealed; the heat doesn’t have an easy access vent like a fan intake. The rear panel exhaust fan also helps keep this heat at bay, particularly if it is complemented by a front intake fan on the opposite side, or an in-line fan on a tower CPU heatsink that keeps all the air flowing in a line front-to-back. The Solo II also happens to have a number of quiet features — heavy 1mm panels, very sturdy construction, polycarbonate sheets on panels for vibration damping, and a hard drive floating suspension system. A fanless power supply suggests a silent system, and silence is the Solo II’s raison d’être.
The best microATX candidate is the SilverStone Temjin TJ08-E. The layout is odd, similar to a modern tower only flipped upside-down. The end result is well suited for a fanless power supply as it sits at the top with a dedicated exhaust vent. It has a massive 18 cm intake fan at the front, and a 12 cm position at the rear next to the CPU, so not much heat will waft up from the graphics card and processor. The fan setup might be better than the Solo II, but the top vent is smaller and the entire case is more cramped (see how the hard drive cage overhangs the motherboard tray).
SilverStone Temjin TJ08-E.
SAMPLE FANLESS PSU SYSTEM BUILD
As a proof of concept, we built a system with a Seasonic X-400 in the Antec Solo II case. Passively cooled power supplies have mostly been used for low-end systems but we went with more mainstream components for a mid-range gaming system to show you just what the X-400 is capable of powering, and how cool and quiet such a system can be. It is actually at higher loads that this new breed of super-efficient, fanless PSU shows its best advantage; this is when the fan in a conventional PSU begins to speed up and become a significant, audible source of noise.
CPU: Intel Core i5-2500K.
Motherboard: Asus P8P67.
RAM: 4GB Kingston HyperX LoVo DDR3-1600.
While many of us are waiting for Intel’s Ivy Bridge and AMD’s Bulldozer platforms to drop, Intel’s Sandy Bridge processors remain the best performing chips on the market. The 3.3 GHz 95W Core i5-2500K is incredibly popular amongst enthusiasts due to its reasonable price and unlocked multiplier. If you’re an AMD fan, you may prefer a cheaper Phenom II X4/X6 processor, but you’ll be sacrificing both performance and in particular, energy efficiency, which is vital in a quiet PC build.
As motherboards go, the Asus P8P67 is rather modest in terms of features but having a stacked board isn’t vital for this build. It does have three controllable fan headers, which means we didn’t need a dedicated fan controller.
For RAM, we picked out a 2x2GB kit of Kingston HyperX LoVo DDR3-1600. As computer memory is dirt cheap at the moment, it’s perfectly reasonable to go with 8GB as well if you’re so inclined. Brand is not terrible important given that RAM is effectively a commodity; Other well-known names like Corsair, Crucial, G.Skill, Mushkin, and OCZ are just as good as Kingston. We do recommend DIMMs rated for 1.5V or lower, as in our experience, they tend to be more compatible with a wider range of boards. These Kingston LoVo sticks run at 1.35V and sports spiffy green heatspreaders, a nice change from the usual fare.
CPU cooler: Thermalright Venomous X.
There are a number of huge dual 14 cm CPU heatsinks from Prolimatech, Noctua, and Thermalright, but the smaller and cheaper Thermalright Venomous X and Ultra-120 eXtreme produce very similar results. We went with the Venomous X as its wider fin spacing is well suited for low airflow — we wanted to make this machine as quiet as possible. The rock solid, idiot-proof mounting system is one factor that tilted our decision toward Thermalright rather than some of the cheaper value coolers from Scythe, Zalman, and Cooler Master.
GPU & cooler: AMD Radeon HD 6870 & GELID Icy Vision.
The Radeon HD 6870 is a common graphics card found in contemporary gaming builds. Ours is an AMD reference sample with a maximum power draw of about 160W. The stock cooling unit was fairly loud at load, so we paired it with a GELID Icy Vision to keep temperatures and noise level to a minimum. Various manufacturers make 6870’s with similar style dual fan heatsinks, but they’re nowhere near as formidable as this five heatpipe, 1 lb beast. The Icy Vision’s two 92 mm fans are connected to a 4-pin connector that fits our card’s fan plug, but it lacks the PWM wire required for the 6870’s built-in fan control system. We powered it using the included 3-pin/molex adapter.
Case fans: Scythe Kaze-Jyuni (Slip Stream) 120 mm.
The Solo II ships with a single TrueQuiet 120 mm fan at the back — this is an exceptionally quiet fan! — and two optional 120 mm positions at the front. For a low-end graphics card or integrated graphics we would probably be satisfied with just the one case fan, but with a high-powered GPU in the mix, some supplemental cooling seemed appropriate. The Scythe Slip Stream line performs well, have very smooth acoustics, and is inexpensive and widely available. We went with two 500 RPM models (SY1225SL12SL) for the front intakes and a 1300 RPM PWM variant (SY1225SL12LM-P) for the Venomous X CPU heatsink.
SSD: Kingston V+100 96GB.
HDD: WD Caviar Green 2TB.
ODD: Asus BC-08B1ST.
No silent system is complete nowadays without a speedy SSD, so we popped in a Kingston SSDNow V+100 96GB into our rig. It is completely silent but fairly expensive per byte. 96GB isn’t enough for most users so we added a 2TB WD Caviar Green for good measure. The Caviar Green is the ultimate low noise/vibration/power drive, but 7200 RPM models aren’t out of the question as the Solo II has elastic suspenders that will cancel out the noise of higher vibration drives. We also went with an Asus BC-08B1ST Blu-ray drive, though depending on how you prefer to consume media, leaving an optical drive off the build list completely may be perfectly acceptable.
As the Solo II has an orthodox layout, assembly is straightforward if you’ve ever built a tower PC before. The front bezel has to come off to install drives and intake fans, and the power supply and motherboard mount in the usual manner.
Though the case is somewhat cramped, there are enough nooks and crannies for tidy cable management.
TESTING & VALIDATION
System device listing.
Measurement and Analysis Tools
Our test procedures involve putting the system in various states (idle, playing HD video, CPU stress, CPU and GPU stress) and monitoring system temperatures, power consumption, and noise levels.
Fan Control Setup
Fan control diagram.
The P8P67 has four fan headers, three of which can actually be controlled, and one of which supports only PWM control. The 500 RPM Scythe intake fans didn’t require slowing down at all, so we connected one to the full speed PWR_FAN header in the top right corner and ran the second off with the power supply by using an included 3-pin to molex adapter. The Scythe PWM fan was obvious choice for the PWM-only CPU_FAN header, leaving the CHA_FAN1 and CHA_FAN2 headers for the rear Antec fan and the GELID Icy Vision.
Fan control setup.
We relied on Asus’ Fan Xpert utility to get a hold of fan speeds; It allows users to alter fan speed behavior with a customizable CPU temperature vs. fan speed graph. We set the CPU fan to increase linearly from 20% at 0°C to 45% at 45°C.
Fan control setup.
The Chassis fan settings which controlled both the rear exhaust and GPU fans had a minimum speed of only 50% so we decided to leave it flat. This was suitable for the included 1000 RPM Antec exhaust fan, but proved to be unnecessarily high for the GPU Cooler. The GELID Icy Vision is an outstanding heatsink, requiring very little airflow to produce excellent results so we supplemented the motherboard fan control with a Zalman Fan Mate to make it as quiet as possible.
Asus PC Probe readout.
According to Asus’ PC Probe utility, on load our final fan speeds were ~810 RPM for the CPU fan (45% setting), ~560 RPM for the rear exhaust fan (50% setting), and ~530 RPM for our front intake fan (full speed). The GPU fan rat at ~1300 RPM (50% setting) but we dialed the knob of the Zalman Fan Mate back to bring it down to ~1060 RPM. PC Probe only displays the CPU and motherboard (PCH) temperatures so we also used SpeedFan which recognized thermal sensors on the SSD and HDD.
To start things off, we put the system on full load and tested to see which intake fan position gave better results, and whether it was worth the extra noise to use both fans.
System Measurements: CPU + GPU Load
System Power (AC)
Noise Level @1m
Ambient temperature: 24°C.
Internal PSU temperature: 52~53°C.
The CPU and GPU temperature were hardly affected by the position of the fan. The bottom positioned favored the board’s PCH chip to the tune of 6°C, while the upper fan provided a 6°C boost in HDD and SSD cooling (both drives sit directly in front of it). The two fans combined brought us the best of both worlds and also reduced the GPU and GPU VRM temperature by 2~3°C. As the fans we employed ran at only 500 RPM, the noise increase from the second fan was about half a decibel, making it a no-brainer to double up.
The X-400 power supply itself remained fairly cool on heavy load. Scanning the interior of the power supply with an IR thermometer showed that the hottest points were under 55°C.
CPU + GPU Load
System Power (AC)
Noise Level @1m
Ambient temperature: 24°C.
When sitting idle and playing video, our system stayed very cool with the CPU temperature staying under 40°C. The CPU fan spun ~100 RPM lower than at load, reducing the noise level slightly to 17 dBA@1m. The efficiency of the i5-2500K is noticeable in our load tests. Stressing the CPU alone raised power consumption by a modest 54W — adding a GPU load on top of that required an extra 148W on top. Sucking down 277W, the X-400 is about 91% efficient, making the total power output 252W, approximately 63% of the power supply’s rating so there was some headroom for more powerful hardware still.
So how does did this build sound? Well at 17~18 dBA@1m, the volume of the system was quite low, and what was audible was very smooth, sounding like a pleasantly gentle ‘whoosh.’ This isn’t really a surprise as each component was selected for superb acoustics. We used smooth sounding fans, the quietest hard drive on the market (suspended for good measure), a completely silent SSD, and a case with thick construction and dampened side panels.
These recordings were made with a high resolution, lab quality, digital recording
system inside SPCR’s own 11 dBA ambient anechoic chamber, then converted to
LAME 128kbps encoded MP3s. We’ve listened long and hard to ensure there is no
audible degradation from the original WAV files to these MP3s. They represent
a quick snapshot of what we heard during the review.
Each recording starts with ambient noise, then 10 second segments of product
at various states. For the most realistic results,
set the volume so that the starting ambient level is just barely audible, then
don’t change the volume setting again while comparing all the sound files.
Our sample build may not be the quietest system you can build with a fanless PSU; after all, there were six fans in the mix, even if we did run them at very low speeds. We could have thrown together an even quieter system with integrated graphics or lower powered, passively cooled VGA card and just a single case fan. But not only would it have been boring — that kind of minimalist system is bread-and-butter at SPCR — it would have posed little challenge for the power supply.
The Seasonic X-400 proved its worth, effortlessly driving our powerful system with an Intel Core i5-2500K processor and a Radeon HD 6870 graphics card in a case with very low speed fans. An important aspect of its performance is that because there is no thermally fan controlled fan in the PSU, the system never changes its acoustic character, regardless of load; there is no fan speeding up or slowing down to attract your attention.
It should also be noted that the Seasonic’s current US$90 price-tag isn’t far off from an ultra quiet actively cooled model like the Nexus NX-5000. The amount is just a drop in the bucket in the context of the total cost of our system, about US$1,160.
Approx. Price (USD)
Intel Core i5-2500K
Thermalright Venomous X
Kingston HyperX LoVo 4GB DDR3-1600
Radeon HD 6870
GELID Icy Vision
Solid State Drive
Kingston SSDNow V+100 96GB
WD Caviar Green 2TB
Asus BC-12B1ST (BC-08B1ST discontinued)
Antec Solo II
3 x Scythe Slip Stream 120mm, Zalman Fan Mate
*after mail-in rebate
We hope this guide helps those considering a PC build with a fanless PSU. The machine we assembled can be used as a blueprint for a general silent PC with varying degrees of horsepower. Just remember to experiment thermally using stress testing and temperature monitoring software before finalizing settings.
Our choice of case, the Antec Solo II, is ideal for a passively-cooled machine but it works just as well with a regular power supply. Like its predecessor, the Solo II has some nice silent-oriented features. It you’re looking for something smaller, the SilverStone Temjin TJ08-E is a good microATX alternative, better for a power system than the more cramped Antec NSK-3480 (a 5-year old MATX design that happens to have a top vent for a top-mounted PSU). Many of the other parts we’ve chosen (CPU, motherboard, RAM, optical drive) can be substituted with parts that meet your individual needs without significant acoustic impact.
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Articles of Related Interest
Silent Mid Gaming PC Build Guide
Silent SFF Gaming PC Build Guide
HTPC Home Server
Gaming/Home Server: HD 5780 + 9 HDDs
Mid-Tower Home Server Configurations
SFF Gamer/File Server V2
Kingwin Stryker STR-500
Fanless PSU Torture Test Roundup
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