I'm considering trying P183 since the upcoming P280 is really disappointing to me.

If it's placed in the lower chamber, will the heat be accumulated since there is no way to get hot air out?

I think it should work. There is less passive air flow, maybe, but also there is no heat from the CPU and GPU, etc.

Doesn't the P183 have a fan in the center of the lower chamber? If so, it could be thermally controlled and/or cool the hard drives in the lower chamber.

Thanks, Nail.

Yes, the middle fan can be the final solution.

The P183 has a fan in front of the drive cage, I think. Even a very slow-turning slipstream or similar will take care of the cooling needed, with very little noise "penalty".

The P183 V3 has many places where a fan can be placed, but only comes with top and rear case fan.

I am not sure a fan is needed, since there is clearance above and below the PSU when installed in a P183, and the PSU can vent out the rear. You can also open some sliding vents on the top of PSU chamber to let some heat rise to motherboard area above it heat becomes an issue.

If the PSU were installed at the top of a case, it would have to deal with all the other heat in the case which reaches it from all the other components, because hot air naturally rises (no matter how many rear case fans you have), so bottom mount PSU cannot be any worse than that.

To be safe, I installed a Seasonic X-660 (X-560 would be fine in most situations) in my P183, which acts like a fanless PSU until power draw reaches a certain level (which would be more than casual use in my system).

I was thinking of a similar setup, a x-400 or 460 (460 was the cheaper psu here for a while, not sure if it still is) in a p182. Currently I have a 350w psu for my i5 / hd6850 computer.
Now, I do encoding and some gaming, but the x-400 should be fine, right? I mean, even after ~24h of 100% cpu load? Would it be wise to put a fan in the lower chamber? I have 3 hdds down there at the moment, but they're not warm enough to warrant a fan.

I think its smart to use a very slow fan for the front/bottom P183. a slipstream 800 RPM is a decent choice (or any other low RPM you can find). The P182 has a bottom/center that needs a fan swap IMO since the Antec tricool is too loud and too fans for its purpose.

X-400 can probably keep working even without a fan, but if you have HDDs in the bottom its better to have the quiet fan than be sorry later.

What is the point to use a fanless PSU if we have to put a fan to vent it ?

I have an old P180 with an X-400 supply. I have my HDDs in the bottom chamber with the PS and cool the lot with an undervolted Nexus 3-pin fan at 550 RPM. The power supply barely gets warm, and probably doesn't need a fan at all. But as stated above, I prefer to cool the HDDs, and get PS cooling as a bonus.

It all depends on how power hungry your system is. If you do not stress your system too much, the fanless PS should be fine in the P183. When I built my system in the P183, it turned out that my loudest component was my Antec 500 W Eartwatts PS, but only under heavy stress. The Antec CP-850 PS solved the issue completely. It's quiet and efficient. That's what I would do if I were you, especially if you plan to upgrade your CPU and video card in the near future.

This is a good question. The answer is that I already own a fanless PSU and I'm interested in P183 now. For new build, I will never consider this combination.

The point is that you have more control over noise and if you set up the airflow properly you can cool many components with a single fan (HDDs+PSU in the P18x cases).

To expand on this, there are two reasons that a separate case fan gives you more control, especially for super serious silencers:

1) The fan would be installed vertically, which can reduce the chance of ticking/scraping noises developing over time, which would be more likely to occur with a horizontally placed fan
2) If the fan does fail or become noisy, it's easier to replace a case fan, than it would be to replace a fan in the power supply

These points are only really relevant if you've taken a holistic approach to silencing, and want your rig to always have a pleasing noise character.

Every fan has to earn its place, I'd say. Why buy a PSU with a fan?

That's why the Seasonic X series were invented (and their Corsair AX siblings). Best of both worlds. Fanless until the fan is actually turned on and earning it's place