# Top Mount Radiator fan direction



## JustJeff (Aug 21, 2021)

I'm getting back into watercooling after well over a decade away.  I'm not planning any overclocking right away, but I'll probably muck about with it once the system is built.  The system in my specs is what is being built.  The CPU, Mobo, RAM are all sitting in their boxes.  PSU is in my current main PC.  All the watercooling has been sitting in a box for well over a decade.  I'll test the D4 to confirm it's still working.  Radiator needs to be purchased (leaking radiator is what prompted me to stop watercooling).  CPU block needs to be purchased.

For now I have a full tower under my desk.  360 top mounted radiator with fans, 120 fan in front, 120 fan in rear.  One thing other thing to note is that I dont' keep the side panel on.  From the top of my case to the bottom of the desk I have about 6 inches.  It seems that I should pull air in from the top and push it out from the front and back.  If I push air out of the top it's going to deadend into the desk and build up heat.....or so I would think.  The full tower is temporary though.  I'm planning wall-mounted system...but for now I want to get the new stuff in the case and up and running.  I'll finish planning the wall-hung, build it and transfer the hardware to it later.


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## ThrashZone (Aug 21, 2021)

Hi,
I would intake on rads simply because they like coolest air possible
Top and front of cases are also filtered already so rads won't collect dust as fast if maintained weekly

Leaving the side panel off most of the dust will collect in the rad instead of the cases designed filtering system which can also be improved with other materials

Open wall mount not you'd still be smart to concoct a filtering system for it somehow.


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## JustJeff (Aug 21, 2021)

ThrashZone said:


> I would intake on rads simply because they like coolest air possible


Yes, that is how I seem to remember it should be.



ThrashZone said:


> Open wall mount not you'd still be smart to concoct a filtering system for it somehow.


I'm not worried about dust too terribly much.  I have access to compressed air and can regularly blow out radiator fins, fans, GPU, etc.


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## MxPhenom 216 (Aug 21, 2021)

If you are putting rad at the top, those fans should be used as exhaust. Not intake, unless you want to defy physics and push hot air down and into your system....


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## FireFox (Aug 21, 2021)

MxPhenom 216 said:


> If you are putting rad at the top, those fans should be used as exhaust.


Exactly.
I still don't understand why people recommend/suggest top fan as intake
Knowing that someone will quote my post and contradict what i am saying please don't.


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## ThrashZone (Aug 21, 2021)

Hi,
As said because front and top of cases have filters lol


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## FireFox (Aug 21, 2021)

ThrashZone said:


> Hi,
> As said because front and top of cases have filters lol


this


MxPhenom 216 said:


> unless you want to defy physics and push hot air down and into your system....


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## JustJeff (Aug 21, 2021)

MxPhenom 216 said:


> If you are putting rad at the top, those fans should be used as exhaust. Not intake, unless you want to defy physics and push hot air down and into your system....


You didn't address only have 6 inches of space from the case to the desk.  Does that provide adequate air space for the hot air to get out and disperse into the rest of the room? I just ran into this identical situation as a heating and air technician.  Homeowner put a deck over top of their condenser and were burning up fans due to the hot air being pulled through the coil not being able to get out.  All the air was deadpanning into the bottom of their deck, heating up all the air around the unit and getting recirculated back into the condenser.  Their system wasn't running properly and they were smoking their motors.

I'm looking for the best alternative for a temporary situation.  Which is better to draw the coolest air from the top in and let it escape out of the open side panel, or to deadpan the hot air coming off the radiator out the top.  Keeping in mind that the side panel is off and nothing is heat soaking inside the case..


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## MxPhenom 216 (Aug 21, 2021)

ThrashZone said:


> Hi,
> As said because front and top of cases have filters lol


That's irrelevant. If your concern is dust going into a system, well:

1. As exhaust for the top, dust will never enter from that side of the case in that configuration
2. Set up the airflow in the system to be either neutral or positive pressure. Negative pressure will make for a dusty system no matter what.



JustJeff said:


> You didn't address only have 6 inches of space from the case to the desk.  Does that provide adequate air space for the hot air to get out and disperse into the rest of the room? I just ran into this identical situation as a heating and air technician.  Homeowner put a deck over top of their condenser and were burning up fans due to the hot air being pulled through the coil not being able to get out.  All the air was deadpanning into the bottom of their deck, heating up all the air around the unit and getting recirculated back into the condenser.  Their system wasn't running properly and they were smoking their motors.
> 
> I'm looking for the best alternative for a temporary situation.  Which is better to draw the coolest air from the top in and let it escape out of the open side panel, or to deadpan the hot air coming off the radiator out the top.  Keeping in mind that the side panel is off and nothing is heat soaking inside the case..


Thats fine. I see nothing wrong with that. Its not going to really circulate back into the system unless you forcefully make it do that.

Keep it simple,

All you need to do it make sure the air pressure in the system is neutral or positive. 

Neutral: Same amount of air leaving the system as entering 
- Can by done by having the same amount of fans for intake vs exhaust

Positive: This is the best option for a clean system, and cool running - More air entering than actively leaving
- More intake fans than exhaust


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## ThrashZone (Aug 21, 2021)

MxPhenom 216 said:


> That's irrelevant. If your concern is dust going into a system, well:
> 
> 1. As exhaust for the top, dust will never enter from that side of the case in that configuration
> 2. Set up the airflow in the system to be either neutral or positive pressure. Negative pressure will make for a dusty system no matter what.
> ...


Hi,
Wrong again exhaust will draw from where ever it can back/ cracks in the case... unfiltered air plus dude does not use a side panel either lol



FireFox said:


> this


Hi,
Thanks
Rad hot air is nothing compared to other components


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## MxPhenom 216 (Aug 21, 2021)

ThrashZone said:


> Hi,
> Wrong again exhaust will draw from where ever it can back/ cracks in the case... unfiltered air plus dude does not use a side panel either lol
> 
> 
> ...


That will only happen if the pressure in the case is negative. It will have to pull air from somewhere if its got more leaving then entering....

He was referring to what I said as 'this' in response to what you said....


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## FireFox (Aug 21, 2021)

@JustJeff 
My best advice is to try both, intake/exhaust and see what suits you.


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## ThrashZone (Aug 21, 2021)

MxPhenom 216 said:


> That will only happen if the pressure in the case is negative. It will have to pull air from somewhere if its got more leaving then entering....


Hi,
Since there is no side panel being used this is irrelevant read the op lol 
He's also going to be using an open wall mount where there is No Walls except the back lol

Besides once again hottest components are not the radiator but is the CPU depending on clocks/ GPU usually the hottest/ Memory all these components create and run at hotter temperatures than the water will ever get which even under hard oc'ing should top out at 35c


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## Deleted member 24505 (Aug 21, 2021)

Imo top out, front in. The cool air coming in the front will naturally go out through the top rad cooling it. Why have top in which will basically pump warm air from the rad into the case. Say 3 in front and 3 out top will make it neutral so less dust.


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## MxPhenom 216 (Aug 21, 2021)

Gruffalo.Soldier said:


> Imo top out, front in. The cool air coming in the front will naturally go out through the top rad cooling it. Why have top in which will basically pump warm air from the rad into the case. Say 3 in front and 3 out top will make it neutral so less dust.


That is what I have been saying, but at the same time idk if that holds up when you have a case without the side panels on it.


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## ThrashZone (Aug 21, 2021)

JustJeff said:


> Yes, that is how I seem to remember it should be.
> 
> 
> *I'm not worried about dust too terribly much.* * I have access to compressed air and can regularly blow out radiator fins, fans, GPU, etc.*


Hi,
Your call 
It's much easier to remove a filter and vacuum the dust off or take it outside and blow it off "which I do both" rather than doing all this inside the house where the dust bunnies are still in the house.



MxPhenom 216 said:


> That is what I have been saying, but at the same time idk if that holds up when you have a case without the side panels on it.


Because seems like everyone is commenting on the title not the second paragraph in the op lol


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## maxfly (Aug 21, 2021)

I would do which ever is easiest. With no case door it isn't going to matter. Your components are going to be pulling cool air no matter how you set up your rad fans (including the rad). Its a temp build anyhow, so just build it to be taken apart easily is my best advice.
Once you go with your wall mount, figure out which way your fan orientation is going to be most effective. 
 Btw the only time natural convection is actually a factor in an enclosed environment is if your running a fan less rig. The moment you introduce fans you introduce pressure. This immediately forces the air to go where the fans are pushing it or pulling it. If convection were any kind of real factor in case cooling, every case would be built with fans on the bottom and top only.


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## eidairaman1 (Aug 21, 2021)

Passing through a Rad you need high static pressure fans. If the rad is inside the case you need to ensure hot hair has other means of escaping.


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## Deleted member 24505 (Aug 21, 2021)

with no side panel, put the rad where it is most convenient, as air flow is irrelevant.


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## mtcn77 (Aug 21, 2021)

MxPhenom 216 said:


> If you are putting rad at the top, those fans should be used as exhaust. Not intake, unless you want to defy physics and push hot air down and into your system....


This is wrong. If you make it the exhaust side, the fan motor ambient temperature will increase - reducing MTBF. Also, I would be reticent to put any cheap sleeve bearing fan in a vertical axis orientation for the proper lubrication can only work horizontally.
The exhaust side can work on its own pressure difference if you seal the case properly. Cold air has higher inertia, if multiple fans work as intake, the air turbulence can reduce air insulation.


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## claes (Aug 21, 2021)

mtcn77 said:


> This is wrong. If you make it the exhaust side, the fan motor ambient temperature will increase - reducing MTBF. Also, I would be reticent to put any cheap sleeve bearing fan in a vertical axis orientation for the proper lubrication can only work horizontally.
> The exhaust side can work on its own pressure difference if you seal the case properly. Cold air has higher inertia, if multiple fans work as intake, the air turbulence can reduce air insulation.


Sorry to troll but this post doesn’t make sense.

My best reading is that you’re worried about fan motor temperature and therefore think intake is better than exhaust. This might be true (although probably irrelevant), but doesn’t address any of the claims made in the post. Therefore you haven’t made any claims as to why they’re wrong, only an aside (fan operating temperature) that could be a potential downside to exhaust that the OP should consider.

The second paragraph makes logical sense but ignores that the OP is planning on running the case without a side panel.


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## Outback Bronze (Aug 21, 2021)

ThrashZone said:


> I would intake on rads simply because they like coolest air possible


 
Agreed. Been WC for decades...


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## JustJeff (Aug 21, 2021)

FireFox said:


> @JustJeff
> My best advice is to try both, intake/exhaust and see what suits you.


Yep, I have thermometers for the purpose of measuring supply and return air.  I'll just set my thermometers in the system and measure the deltaT.

I got my answer and it seems that people are going to muck up the thread debating the general issue without actually having read the specifics of the OP


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## mtcn77 (Aug 21, 2021)

claes said:


> Sorry to troll but this post doesn’t make sense.
> 
> This might be *true* (although probably irrelevant), but *doesn’t address any of the claims made in the post.*


Well, since it is 'my' post to address, it does relate to the claims I set as long as it is still true, which you have also recognised. That makes it self explanatory doesn't it? I don't claim something, I just simplify the train of thought.
If you want to digress, I'd be happy to, but that would be beside the point. Why and how cooling works are different inflection points. I'm trying to sequence the second part. If you think you can increase cooling by not attending to the pressure losses, or thinking air can go where it takes sharp turns(as in oversize fan blowing on the open case) think of it like a car engine and some seals...

The clearest path and the shortest trajectory of fan volute wins.
PS: I forgot some fans do not operate in "pull" quietly, but since we are discussing radiators, I'm expecting there is a way to stack the fans before the radiator?


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## claes (Aug 21, 2021)

Mxphenom was talking about pulling hot air from under the desk
You’re talking about hot air affecting fan life span

I’m not arguing with you, I’m just explaining that telling someone that they’re wrong without addressing their claims doesn’t address why they’re wrong.

Besides being a little rude, in the context of this thread, if we’re to assume that what mxphenom said is true and that hot air will collect under the desk, then you’re technically agreeing with them.

Have a good one


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## mtcn77 (Aug 22, 2021)

claes said:


> I’m just explaining that telling someone that they’re wrong without addressing their claims


As again, you are reading it as dispositional reference whereas it is situational reference. I didn't put any connotation on his claim, that would be rude. I said it as a principle. You are taking the explanation as the criticism.



claes said:


> if we’re to assume that what mxphenom said is true and that hot air will collect under the desk


While true, that would be fallacy of intent. Just because setup is wrong like he said it would be, is no judge of his character. I'm not saying "you are wrong", I'm saying "that is wrong". Those are two different statements. One has no referencial meaning, only contextual.


maxfly said:


> Btw the only time natural convection is actually a factor in an enclosed environment is if your running a fan less rig. The moment you introduce fans you introduce pressure.


Hi, while true, pressure is only sustained for a little while, so it is better to say the moment forced convection is introduced, you introduce a pressure loss gradient. Air doesn't work like liquids. What you say is more relatable to water coolers.


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## claes (Aug 22, 2021)

You can bring a horse to water etc. Whatever suits you I guess


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## crazyeyesreaper (Aug 22, 2021)

1) put the damn side panel on
2) adequate air intake at the front
3) exhaust hot air out of the system via the top
4) position fans as pull fans meaning top of case > fans > radiator, this will result in dust accumulating on the radiator but thats easier to remove / clean than the fans themselves.
5) yes 6 inches is enough space. if its under a wide open desk it wont be a problem. The fans positioned as noted above will have more force and continually push the hot air up and outwards.

Essentially if your only going to watercool the CPU and no GPU as of yet. your literally worry about a bunch of details that you don't need to. Now if your gonna watercool a 3090 or something then yeah might be more worthwhile to use the extra brain cells. But overall its a moot point. Air intake up front exhaust out the top and be done with it.


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## mtcn77 (Aug 22, 2021)

claes said:


> You can bring a horse to water etc. Whatever suits you I guess


Are we talking about the same subject? Randomness has no place in pc cooling. It needs meticulous inquiry to work properly. Connecting intake and exhaust fans inside the same slipstream has a dual purpose of amplifying air pressure. Connecting an oversize fan won't benefit this at all. Sometimes even work to the detriment, as it might create insulating air pockets since it might be pushing air against the direction of heat flow, breaking laminar flow characteristics that improve air pressure and reduce heat pockets.



crazyeyesreaper said:


> 5) yes 6 inches is enough space. if its under a wide open desk it wont be a problem.


It will have reflected heat, though. Pretty bad, just like high internals. I would caution against it. Pc cases work just like column radiators. Air circulates around them and cold air inside the room gets accelerated towards it, but this slows down if its upstream(really up, like vertical into the ceiling) gets impeded and it starts getting isolated from the cold air in its own heat pocket.


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## Deleted member 24505 (Aug 22, 2021)

I'm sure you mean a D5 pump too, not D4


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## DeathtoGnomes (Aug 22, 2021)

OP could put a fan outside above the case to direct the hot air out from that small space.


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## maxfly (Aug 22, 2021)

Gruffalo.Soldier said:


> I'm sure you mean a D5 pump too, not D4



Its the predecessor to the d5. An oldie but a goodie


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## Deleted member 24505 (Aug 22, 2021)

maxfly said:


> Its the predecessor to the d5. An oldie but a goodie



Aah never heard of the D4


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## mtcn77 (Aug 22, 2021)

@claes don't hate me pal. I am not smart enough to pull off an engineering feat in explaining how much flow redirection affects air flow impedance, but it is there. It is a slow taper to zero convection, inverse to fan distance, and just like helicopter blades there is a sonic limit to how fast fans can start with the pressure gradient until the count down to zero begins. Better fans just replicate a volute closer to the fan and a categorical worse fan is like a stock fan that is pushing air through the bends in a really crowded case.


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## MxPhenom 216 (Aug 22, 2021)

mtcn77 said:


> Are we talking about the same subject? Randomness has no place in pc cooling. It needs meticulous inquiry to work properly. Connecting intake and exhaust fans inside the same slipstream has a dual purpose of amplifying air pressure. Connecting an oversize fan won't benefit this at all. Sometimes even work to the detriment, as it might create insulating air pockets since it might be pushing air against the direction of heat flow, breaking laminar flow characteristics that improve air pressure and reduce heat pockets.
> 
> 
> It will have reflected heat, though. Pretty bad, just like high internals. I would caution against it. Pc cases work just like column radiators. Air circulates around them and cold air inside the room gets accelerated towards it, but this slows down if its upstream(really up, like vertical into the ceiling) gets impeded and it starts getting isolated from the cold air in its own heat pocket.


Sounds like we have a freaking HVAC expert in here


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## maxfly (Aug 22, 2021)

MxPhenom 216 said:


> Sounds like we have a freaking HVAC expert in here



Sometimes its best to just walk away


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## MxPhenom 216 (Aug 22, 2021)

Looks like we are talking about helicopters now...


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## crazyeyesreaper (Aug 22, 2021)

mtcn77 said:


> Are we talking about the same subject? Randomness has no place in pc cooling. It needs meticulous inquiry to work properly. Connecting intake and exhaust fans inside the same slipstream has a dual purpose of amplifying air pressure. Connecting an oversize fan won't benefit this at all. Sometimes even work to the detriment, as it might create insulating air pockets since it might be pushing air against the direction of heat flow, breaking laminar flow characteristics that improve air pressure and reduce heat pockets.
> 
> 
> It will have reflected heat, though. Pretty bad, just like high internals. I would caution against it. Pc cases work just like column radiators. Air circulates around them and cold air inside the room gets accelerated towards it, but this slows down if its upstream(really up, like vertical into the ceiling) gets impeded and it starts getting isolated from the cold air in its own heat pocket.


Doesn't change the fact that if he is running a CPU only loop it wont matter in the grand scheme of things. If the loop has a high TDP GPU then that would be different. However a 10700KF even OCed heavily will only be around 250-260-watts when manually OCed unless trying to push extreme clocks. Considering the real world testing data I have available to me. It literally is a moot point for one major reason. No one actually using a PC will tend to have it pegged at 100% 24/7 meaning the heat exhausted under the desk will change depending on load and if its gaming / browsing / typical work that variance in power draw means there is no consistent heat exhausted meaning it has time to dissipate.


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## HammerON (Aug 22, 2021)

For the past year and a half I have had two pretty much exact systems running 24/7 in separate cases.  They were both 3900X crunchers.  In my main rig, I had the fans on the top mounted 360 rad as an exhaust.  On the other I had them set as intake.  The main reason I did this was the second rig only had a water block and not a mono block cooling the VRM.  I wanted the air from the fans (even though it may be slightly warmer) blowing over the VRM heatsink.  Both systems had one 360 rad and D5 pump.
Anyways, both systems were clocked to 4.1GHz with the same 1.18 Vcore.  Both systems ran at the same CPU temperature, which was ~62c.  VRM was a little hotter on the second rig (the one w/out the mono block) but well within limits.
Now the interesting thing is, just last week I took both systems apart to upgrade and clean as they had been going for about 1.5 years.  What I found was that the second rig had a lot less dust inside.  But the case is also a little better than the other Thermaltake case that the first cruncher is in.  So not apples to apples exactly.

From my experience water cooling for some time now, it really doesn't make too much of a difference.  But that is just my experience and I am by far no expert


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## MxPhenom 216 (Aug 22, 2021)

HammerON said:


> For the past year and a half I have had two pretty much exact systems running 24/7 in separate cases.  They were both 3900X crunchers.  In my main rig, I had the fans on the top mounted 360 rad as an exhaust.  On the other I had them set as intake.  The main reason I did this was the second rig only had a water block and not a mono block cooling the VRM.  I wanted the air from the fans (even though it may be slightly warmer) blowing over the VRM heatsink.  Both systems had one 360 rad and D5 pump.
> Anyways, both systems were clocked to 4.1GHz with the same 1.18 Vcore.  Both systems ran at the same CPU temperature, which was ~62c.  VRM was a little hotter on the second rig (the one w/out the mono block) but well within limits.
> Now the interesting thing is, just last week I took both systems apart to upgrade and clean as they had been going for about 1.5 years.  What I found was that the second rig had a lot less dust inside.  But the case is also a little better than the other Thermaltake case that the first cruncher is in.  So not apples to apples exactly.
> 
> From my experience water cooling for some time now, it really doesn't make too much of a difference.  But that is just my experience and I am by far no expert


That is kind of what I was getting at regarding negative vs neutral vs positive pressure and the difference between the 3 regarding how clean the system is. Temps would be pretty negligible between the 3 configs.


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## ThrashZone (Aug 23, 2021)

Hi,
Bad thing about top exhaust and being under a desk is the exhaust air is going to be in the op's lap/ belly instead of at his feet 
Might be good for winter warming but bad in the summer.


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## mtcn77 (Aug 23, 2021)

Again, experience is the best lesson. Air surrounding the pc case works like an heat engine. If you let it isolate itself from the convection currents surrounding the room sitting under its desk like a drawer, it won't work properly.

There has to be a good contact between the heat source and the cold plate in order for the Stirling Engine to work properly according to the temperature difference and similarly, the case has to be in open circulation to make good contact with the convective air stream.


MxPhenom 216 said:


> Sounds like we have a freaking HVAC expert in here


Yes, sweety.








He just recirculated the idea of the original Cosmos case with its back to front gpu air duct. Next time tell me something new when you feel on top of things.


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## MxPhenom 216 (Aug 23, 2021)

Damn, he's arrogant too. Nice


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## Jetster (Aug 23, 2021)

FireFox said:


> Exactly.
> I still don't understand why people recommend/suggest top fan as intake


Positive pressure, you can still direct the heat out the top back.
OP just put it anyway that works for you. Then check your temps


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## DeathtoGnomes (Aug 24, 2021)

Jetster said:


> Positive pressure, you can still direct the heat out the top back.


There are limitations to this, mostly depending on the case (and its size).  In a situation like this, the case is in close quarters under a desk, I'd go as far as ghetto mounting an extra rear exhauset fan just to make the top mounting (as intake) more flexible temp wise. it still might be up a couple degrees but shouldnt overheat rapidly


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