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So I got condensation in my PC for the first time today :P

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So basically winter caught me off guard and I woke up to this:

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I am using external watercooling with MO-RA3 placed in a different room on the attic that is not actively heated. Tonight, the temperature outside went down to -5C suddenly, which caused that room to cool down to like 5C.

Normally that wasn't the problem, because my entire system was watercooled and it was dumping all its 500-1000W heat into that room, so it was never really going down below like 8-10C, and ambient inside the case was roughly the same as my room ambient, around 18C/40%RH, even with panels closed because some slight radiation from blocks and tubes was the only heat source there, so dew point remained around 5C. I was using this setup already for 2 years with 6900K/2080Ti SLI system and it was always within safe margins.

Right now though, I do not have the block for 4090 yet so not only I am not dumping any real heat into radiator room, but the GPU is heating up the case ambient even at idle and with side panels open, so the ambient in radiator room went down to 5C, and case ambient went up to 25C, resulting in dew point around 11C, so water was whole 6C below dew point. And of course, I fell asleep yesterday, so PC was idling like that the entire night :p

Fortunately, it is all jerry rigged together randomly before I get the block so I kept paper towel on the GPU backplate. After closely inspecting the case and the paper towel though, there were no droplets that actually dripped down, which is pretty good considering that it was left like that for hours and water temperature was 6C below dew point. Also, the CPU block was perfectly fine with no signs of condensation, so I guess the ~25W that the CPU draws idle was enough to keep it warm.

Very interesting start of the day :p It is a pretty good experience though, 6C below dew point with air cooled card dumping some hot air into the case, even if idle, sounds like it should be an absolute disaster, and it wasn't that bad really. It took forever for condensation to form, and it still didn't drip, although it was quite close. With all watercooled parts and insulated tubes you can probably run below dew point just fine, GPU and CPU blocks have enough of their own heat even at idle to stay warm, only parts that do not are a problem it seems.
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Nice you caught it in time. Warm, moisture latent air will condense on cold surfaces.

Once you get that GPU on water, your loop temp will go up but you also lose a local source of heat (convection and radiation).

You know why [building] radiators are traditionally placed under windows? To mitigate condensation.

You can’t control the outdoor temp so it’s quite risky.

I wouldn’t be comfortable running that system when your loop temp is below dew point. You’ll have to insulate your blocks too. Otherwise you may find condensation on your 4090 block.

In other words, be careful! I’d find a location for that rad where temps are more stable. Even if warmer.
 

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^ That only works assuming your temp in the attic stays at a constant temperature or doesn’t drop further.

Assuming you live in Poland, I know most residential houses don’t insulate the roof. Rather it’s the ceiling plane beneath the bottom of the roof trusses or beams. Or in other words - the attic is unconditioned.

It can get also get quite cold in the winter. Not as frequent or drastic as Canada… but I’ve spent a lot of time in małopolska, and it does drop to negative temps frequently in the winter.

As long as you’re confident a constant 400-500w being exhausted by your radiator will maintain a decent temp in your attic, you’re OK. An idle system will keep blocks warm, sure… but your loop temp could still be below dew point on very cold days and you still risk condensation.

I also still think you’re underestimating how the air cooled 4090 is influencing behaviour in your case. Dew point isn’t just based on ambient temp.

I would advise reconsidering the location of the rad or at least insulation. Even a semi-enclosed enclosure around the rad to mitigate some of the cold is an option.

The risk for a short is high given the volume of most attics and the unknown temperatures of an unconditioned attic in the winter.
 

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Ah - you’ve should of clarified from the start it was a conditioned space! This my frame of reference:
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Look - my posts were just to flag the risks and seems like you’re on top of it. Just don’t want to see you fry your hardware :)
 

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My main room is conditioned, radiator room isn't, but it is insulated, not very well and roof window is very old and not good, but still :p
OK not technically conditioned (besides your PC) but it’s within the building envelope and some heat loss from below will be contained in that space.

Very different than just an uninsulated attic.
 

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Nah, just need to throw more heat in there and things will be great! Curious as to what OP does in the summer, however. With the temperature swings we have in the states, there is no way that would fly here.We can go from -11 to +38C from winter to summer in a NORMAL season in the northeast.
Yup. I’m in NE Canada, eh. Typically get as low as -25C and high as 35 (without windchill or humidity). Nice 60C delta.

Chiller, geothermal, heck tying your loop into in floor heating. Lots of options :)
 
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