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HEATSINKS AND COOLING
The A8N32-SLI is one of very few nVidia-based boards that is passively
cooled. This is possible thanks to an elaborate system of copper heatpipes and
heatsinks that transfer the heat away from the chipset bridges. Of course, it's
not enough just to move the heat around. Eventually, the heat needs to be exhausted
from the case.
To this end, the main heatsink for the chipset is located between
the CPU socket and the rear connectors. The basic idea is to move the heat from
the chipset into the exhaust airflow path from the CPU heatsink, which is almost
guaranteed to have a fan. Even if the CPU is being cooled passively however,
the case fan in a well designed system should provide airflow in the right place.
If it doesn't ASUS has included a small blower that can be used as a last resort.
A stack of copper fins puts the heat from the chipset in the exhaust of the
CPU heatsink.
How does the heat get up to that part of the board, you might
ask. Or, if you've already looked at the pictures, you might not, since you'll
already know that the answer is heatpipes. Two copper blocks — one each
on the northbridge and the southbridge — are used in place of the more
conventional aluminum heatsinks, and two heatpipes, one from each chip, carry
the heat up to the top of the board.
Copper blocks with heatpipes instead of aluminum heatsinks.
It should be no surprise that the all-copper design is quite massive in both
size and, well, mass. This is by far the heaviest motherboard we've encountered
— it's so heavy we were almost afraid to move it around much in case it cracked
under its own weight!
Perhaps a bigger concern is how the layout of the heatpipes will affect compatibility
with various heatsinks. As the photo below shows,
clearance is a bit tight around the CPU. Fortunately, the cooling system has
a low profile, and most of the large heatsinks are narrower around
the bottom, as they should be.
Another potential tight spot is above the top PCIe slot. There is not a lot
of clearance between the slot and the main chipset heatsink, and double width
cards with big heatsinks on the back side of the card may not fit properly. Large
graphics cards may be installed normally in the lower PCIe slot, so this issue
probably only applies to users with more than one video card.
Seemingly limited clearance around the CPU...
...isn't really an issue, as the huge Scythe Ninja fits fine and has plenty of clearance.
As long as the board is installed in a ATX tower case with conventional
airflow — especially the back panel exhaust fan — the heatpipes should have no problem keeping the chipset cool. However,
there are potential problems that could arise in a nonstandard setup.
Some of these have been mentioned already: The motherboard is not recommended
for use with passive heatsinks or watercooling setups unless additional airflow
is provided for the chipset.
In addition, cases that orient the motherboard horizontally or
upside down, such as HTPC and some enthusiast cases (Lian-Li PC-V series and Silverstone TJ06 come to mind), may affect the efficiency
of the heatpipes. The reason for this is simple: Heatpipes work best when gravity
helps return the refrigerant from the condensor to the evaporator (in heatpipe lingo). In other words, the
source of the heat should be below the cooling fins that dissipate the heat. That doesn't mean the heatpipes won't work otherwise; as long
as there is a difference in temperature between the source and the exhaust, the coolant will cycle, even if more slowly than usual. But, the cooling system is designed with the
assumption that it will be installed in a conventional case, and it's probably
best not to tinker with it without a lot of planning and testing.
Vital Statistics: YD124515MB, DC12V, 0.13A.
As a safety precaution, ASUS has included a small blower that is designed
to clip onto the chipset heatsink if the cooling is inadequate. Oddly enough,
this "safety feature" comes with a warning that threatens instability
if the fan is installed when it is not needed. This isn't as crazy as it sounds:
The blower is quite tall, and could actually interfere with airflow in a well-designed
system.
The blower is branded Y.S. Tech, but the model number does not show up anywhere
on the internet. Most likely, it is a custom design for ASUS. Its noise signature
is fairly benign — better than most northbridge heatsinks — but it's
still louder than most people will want from a passively cooled board. Because
the passive design is the primary reason why many will consider the A8N32-SLI
Deluxe, we did not bother doing extensive acoustic testing on the
blower.
The backside has an ASUS logo. The blade design is similar to those found
on some recent nVidia VGA cards.
Although the heatpipes carry the bulk of the heat from the motherboard,
there is one heatsink that they do not reach. There is a narrow aluminum heatsink
parallel to the top of the board that cannot count on heatpipes to help it out.
This heatsink is for the MOSFETs that help supply power to the CPU. Although
they do tend to get quite hot, this is the only motherboard we've seen that
has a heatsink specifically for them. Perhaps it is needed for the eight-phase
power regulation that ASUS boasts about...
Like the the main copper heatsink, the aluminum heatsink sits
beside the CPU socket where it can take advantage of the airflow coming off
the CPU cooler. A power supply with a bottom-mounted fan may also provide some
airflow around it, as will a rear-panel exhaust fan.
One last heatsink, this one aluminum.
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