Does Backflow Affect GPU Waterblock Performance?

The ports on GPU waterblocks are not labeled IN or OUT in any way, so you might be wondering if reversing the input and output ports will affect its performance?

The previous generation GPU EK-FC water blocks, as well as the EK-Vector full coverage water blocks, are designed to operate efficiently regardless of coolant flow orientation. Because of this, these water blocks do not have designated inlet and outlet ports, but one installation still has small advantages.

Ideally, the flow of refrigerant enters the microchannels through the burst plate and then flows out from both sides. This flow path effectively splits the liquid on both sides of the fins stack through the hottest part, which is located above the GPU die. After that, fluid fills the rest of the block, the RAM and VRM area, and finally, both streams meet at the outlet.

What happens if you use reverse flow?
Swapping the in and out ports on the GPU water block reverses the path of the fluid: the coolant first passes through the RAM and VRM sections, then enters the fins stack from the sides, exits through the overclocking plate, and flows to the terminal. Sounds completely wrong, but it really doesn’t really matter.

Performance and testing
Through internal testing, we can confirm that the difference in cooling performance when using reverse flow in water blocks is negligible.

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When using the D5 pump on our test rig, the coolant flow rates are virtually the same. 238 l / h at ideal setting compared to 240 l / h in reverse flow. We can easily say that the flow rate is the same in both scenarios, and the small recorded difference is due only to the margin of error during testing.

The temperature difference recorded on the GPU core when using the EK-Vector RTX 2080 Ti waterblock is ideally 1.5 ° C compared to the reverse flow scenario. Yes, only 1.5 ° C. Of course, this may differ slightly depending on which card you have, the voltage at which it operates, if it is overclocked, what is its power limit in the BIOS, etc. But in general, you can expect an average of less than 2 ° C difference in reverse flow versus ideal setting.

What about EK-FC Classic waterblocks?
Like the EK-Vector blocks from the Quantum Line, the performance of the EK-FC GPU water blocks from the Classic line is not too much affected by input and output switching. The internal structure itself is designed so that the accelerator plate reduces the turbulence of the coolant before entering the microchannel zone above the GPU unit.

Therefore, if you are not an overclocker, then we advise you to use the flow path that is most convenient and provides the most aesthetic result. Since using a water block instead of standard air cooling already offers significant temperature improvements, such a small difference in core temperature when using reverse flow isn’t worth sacrificing for the perfect look of your PC.

However, it is worth remembering that CPU water blocks and monoblocks have a strict “in” and “out” orientation and there are much more significant backflow losses.