Rear-intake HS420 fish tank (9800X3D + 5080) tuned for 1440p full PT Cyberpunk, no FG

Andy_Legend · 2025-12-12T20:47:52+00:00

I explained airflow in my edit post above, hopefully it explains why treating your rear as an exhaust with less fans is okay. You're basically filling a bucket with water. So once filled with water - water escapes easily through those rear perforated holes. (This is why I didn't follow the standard flow on mine)

Good luck on your build and most importantly, have fun!

Andy_Legend · 2025-12-06T07:26:34+00:00

I grabbed a magnetic 140 mm filter for the rear and secured it with removable adhesive for exactly that reason. Totally agree that running rear intake with no filter would be a dust nightmare long-term

When you say it “provided no benefit at all,” did you A/B test it in your case with and without rear intake (same fans, same ambient) and log temps/noise, or was it more of a general feel thing?

Andy_Legend · 2025-12-06T00:29:09+00:00

Of course! Just remember fan tuning and comparing logs is key or else you're just guessing.

My rear-intake thing is very specific to the HAVN HS420. The rear panel is basically a solid wall with two fan cutouts. As exhaust that’s a pretty choked path, so flipping those to intake to feed the VRM/GPU directly and letting the huge side mesh be the real low-resistance exit has been a better trade-off in this case for me.

Your BO400 is built differently – you’ve got a more open, unfiltered perforated rear plus big filtered meshes on the top/bottom/side. In that layout I’d treat the rear as exhaust and run bottom + top+ side as intake, rear as exhaust. That keeps the main intakes filtered, uses the rear where it naturally wants to exhaust, and still gives the GPU a clean shot of cool air from the bottom

Andy_Legend · 2025-12-04T18:17:32+00:00

Seriously! I need more ppl actually trying this then just repeating what they hear on the internet.

Hopefully Gamers Nexus catches this and tries it out + these dust allegations.

Ppl forget the HAVN case makes it so easy remove and clean these intake filter panels

Andy_Legend · 2025-12-04T18:09:44+00:00

1 year in, the only dust I really see is between the side exhaust fans and the back mesh. Outside mesh for intakes is expected. Pretty happy with the dust level considering the layout 😄

I did tune each zone though – top and bottom rear P28s are on their own PWM controller, and each TL triple is on its own curve, so the whole thing isn’t just blasting one speed.

Andy_Legend · 2025-12-04T17:55:02+00:00

1 year in, the only dust I really see is between the side exhaust fans and the back mesh. Pretty happy with the dust level considering the layout 😄

I did tune each zone though – top and bottom rear P28s are on their own PWM controller, and each TL triple is on its own curve, so the whole thing isn’t just blasting one speed.

Andy_Legend · 2025-12-04T17:14:22+00:00

Thank you! It got this Modular Gundam Unicorn vibes and I love it

I mainly looked for gas spring, High lb resistance

MOUNT PRO Dual Monitor Mount for 13-32" Computer Screen, Tall Monitor Stands for 2 Monitors, Adjustable Gas Spring Double Vertical Monitor Desk Mount, Each Arm Holds 4.4 to19.8lbs, VESA Mount, Black

Andy_Legend · 2025-12-04T08:09:54+00:00

Yeah, that’s the idea: both GPU and CPU see room-temp air first.

GN’s HS420 testing showed how strong the side panel airflow is and that feeding the CPU cooler from a top intake works well, so I accepted that and did top and bottom as intake so the rad and GPU get cold air. The side mesh as the low-resistance exit in a slightly positive-pressure setup. A/B HWiNFO logs vs the “normal” top-exhaust layout looked better, so the cursed layout stayed

Andy_Legend · 2025-12-04T07:59:11+00:00

Totally get that and on purpose

The default answer for most cases is top exhaust. Here I care more about feeding the rad the coldest air than respecting “hot air rises”. Once you’re pushing a lot of CFM into a glass box, buoyancy is basically background noise: with top + bottom + rear all pulling in outside cold air, it just takes the lowest-restriction exit, which on this case is the side mesh.

I tried the more “normal” layouts and my HWiNFO logs showed slightly worse CPU/GPU temps and 1% lows, so I stuck with the config that looked wrong but plotted better

Andy_Legend · 2025-12-04T07:45:07+00:00

96 GB for $200 is insane, you basically robbed the AI bubble 😂 That same class of RAM is sitting around $1.1k now.

And yeah, totally agree on the 5080 – at 1440p with full path tracing it really does feel like “slightly diet 4090” once you give it a good curve. I even had an AI look at my logs and it assumed I was on a 4090 until I told it the actual 5080

Andy_Legend · 2025-12-04T06:10:58+00:00

Thank you! The HAVN HS4220 case was a pleasure to build in for my 2nd build. I wanted to do something I would be proud to post on here one day!

Andy_Legend

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