Reverse flow direction on Alphacool ES RTX 5090 Reference GPU water block

[Mr Lunar]

I have an Inno3D RTX 5090 Frostbite Pro with the Alphacool ES RTX 5090 Reference 1-Slot water block pre-installed.

Because of my current AIO layout and tubing routing, the coolant flow through the GPU block would be reversed compared to the markings on the block.

I couldn’t find any clear statement in the manual about mandatory flow direction.

Does anyone know whether reverse flow is allowed and safe on this specific ES block, and whether it has any measurable impact on temperatures or reliability?

I’m aware that Alphacool Core blocks with jet-plate designs can be very flow-direction sensitive, so I’d like to confirm how critical this is for the ES series.

Any firsthand experience or official confirmation would be appreciated.

 

[Eddy]

The cooler uses a jet plate system like all modern coolers. If you swap the IN and OUT ports, you can lose up to 10°C in cooling performance. You won’t damage anything by doing so, but the cooling performance will drop significantly.

 

[Bablin1942]

From my experience, Alphacool ES blocks aren’t very sensitive to flow direction, unlike the Core series with jet plates. I’ve run reverse flow without any issues, and it didn’t affect reliability. At most, I noticed a 1–2°C difference, if anything at all. If flow direction were critical, Alphacool would have clearly stated it in the manual.

 

[Eddy]

From my experience, Alphacool ES blocks aren’t very sensitive to flow direction, unlike the Core series with jet plates

The ES coolers also feature a jet plate. The internal design is almost identical to that of the Core coolers.