The Radeon HD 5870 reference cooler design
On the back of the card, there's an aluminium heat shroud, which encloses almost the entire PCB. The only part that isn't fully enclosed is the area behind the GPU, where there's the usual four-point support that ensures a good contact between the GPU and its heatsink.
Removing the shroud reveals very little in the way of components on the back of the black PCB. There are, of course, many surface-mounted resistors, capacitors and diodes on the back, but there are no memory chips - they're all on the front side of the PCB, surrounding the GPU.
The heatsink adopts the familiar radial fan design - this one measures 70mm across and, generally speaking, it's quite quiet. Under load, it does get louder, but it's by no means noisy. The fan doesn’t doesn't spin up or change pitch randomly, for example, and it's nowhere near as loud as the Radeon HD 4890's cooler – I compared the two cards directly by putting them in identical machines sat side-by-side and running the same workloads on the two cards.
The heatsink features four 6mm heatpipes, which transfer heat away from the copper contact point with the GPU into the array of aluminium fins that make up the rest of the cooler. The radial fan blows air across these fins, and then through the vents at the far end of the card. The vents on the PCI bracket are much smaller than we're used to seeing, but AMD has done a good job of channelling air via a duct, to ensure air escapes through the vents effectively.
Not all of the warm air is blown directly out of the chassis though, as there are some vents along the top of the heatsink shroud (in the red plastic portions, for example). Again, there's channelling on the underside of the shroud to ensure that air is ushered in the right direction.
Judging by the size of the vents on the top edge of the shroud and feeling around the area for airflow, we believe that no more than a third of the exhausted air goes back into the chassis. What's more, the card never gets warm to the touch, suggesting that it's pretty good at getting rid of the heat it produces, unlike the Radeon HD 4870 and HD 4890, which were both responsible for a few burnt fingers in the bit-tech
Overall, the cooler is a good bit of design, and superior to Nvidia’s cooler for GT200 cards. For these cards, Nvidia typically augments a rear vent with vents down the side of the card – this leads to GT200-based cards actually dumping a lot of heat into your case despite them having large rear vents. The HD 5870 reference cooler might also dump some heat into your case, but as it’s a cooler card and the rear vent works well, this is less of an issue.