Why do graphics cards have fans on the bottom and heat plates on the top, even though hot air rises? Wouldn’t it be more beneficial to flip that design over and push hot air up?
In: Technology
The fans on a graphics card are intakes, not exhausts. They typically exhaust through the case rear.
You want the cards taking air from below because in most configurations, the other side of the card is near the CPU and its heat sink/fan. Sucking in that air not only hurts the card by taking in warmer air, but hurts the airflow for getting rid of the hot air from the CPU.
The standard for PC expansion cards say that they need to have the PCB on top and the components on the bottom. It leaves very little room on top for any fans and even if there were room the components that needs cooling would be on the other side of the PCB. In fact most graphics cards violate the standard by adding the heat plate to the back and would therefore not fit in tight chassis that are designed around the standard. The plate is also not so much a heat plate but rather a backing plate to help support the heavy heat sinks and fans on the front, it have a minimal impact on thermal dissipation.
The fans on graphics cards are intakes, not exhausts. GPUs actually exhaust through the back of the case, meaning that if you pointed the fans upward, they’d be sucking in warmer air, for exactly the reason that hot air rises.
Not only that, but motherboards and cases are designed with GPUs in mind; flipping the design would require redesigning motherboards and cases to conform, which would be a pain.
Hot air rises, because its less dense and therefore is buoyant compared to the surrounding air. At gpu temperatures this effect isn’t that strong.
A fan overcomes this effect by orders of magnitude, and it doesn’t really matter.
Latest Answers