Bottom-mounted radiator -- how much clearance?

X

Xylo

Limp Gawd
Joined
Jul 5, 2005
Messages
421
In my new system, I'm considering mounting the radiator on the bottom of the case (cutting hole + screw holes, mounting it in)...the fans would naturally be on top, sucking air in through the radiator...

I'm wondering, just how much ground clearance would I need to make this practical and not restrict air-flow?

I also wonder: given enough clearance, would dropping the radiator down outside the case (with the fans still just inside the bottom sucking air through it) give any sort of significant benefits?...anyone have any ideas on this?


Thanks!
Xylo
 
If you have a low speed fan 1-2 cm is enough. It is easy to test by holding you hand and ear to the fan and moving you case up and down and feel if you get less airflow.
Does you rad have any walls around the fins or can the air get in from the side of the rad? if the air can get in from the side it will suck in warm air from inside the case then you might whant to lower it so it is outside the case so all air are comeing from the outside. But if you have walls on your rad and it can only get air from the outside of the case then you don't win anything from puting it outside. Well maybe more space inside the case.
 
About as much clearance as half the width of the radiator is enough for near zero restriction. So if a 12cm wide radiator, then 6cm clearance.
 
I thought that bottom mounted wasn't good? I've always heard pump at the bottom, radiator at the top. Correct me if I am wrong.
 
The only reason why bottom mounted rad is bad is because if you blow air in from the rad you will heatup the air inside your case with the warm water. And if you blow air out from the bottom you are going against the air is going up theory but that is not as bad as it sounds.
Mounting the rad at the top can cause all air in the tubes to rise and stay in the rad. The best is to have the res at the top. But many people have the rad at the top and res at the bottom it is working fine, after some hours the air is removed anyway
 
There's really no signifigant problem with exhausting out the bottom of the case, I did it on my test build to try it out and got almost exactly the same temps as when the radiator was mounted on top. The build I'm working on right now has a bottom mounted radiator with exhaust out the bottom. Do not intake into the case, that's adding temperature to the ambient case temps and defeats the purpose of water cooling.

The advantage to pump on bottom, radiator on top is that you run less risk of trapping air bubbles in the pump housing (very bad) and the pump is fed by gravity rather than suction.

Yes, warm air rises. We'd need someone to calculate exactly how fast the air from a typical radiator rises based on it's temperature. That calculation would need to first be made assuming no air current. Then consider that you'll have a fan moving about 30-60 CFM. That's more than enough to overcome the convection of the warm air and still exhaust the majority of the heat.
 
Even with 2 slow 120mm fans on my radiator, the air coming out is still cool. I wouldn't worry about warming up your case because of the radiator.
 
Cathar said:
About as much clearance as half the width of the radiator is enough for near zero restriction. So if a 12cm wide radiator, then 6cm clearance.
Click to expand...

Perfect, thank you.
 
So you will be sucking air from below your case, and exhausting it into your case?
 
BellaCroix said:
There's really no signifigant problem with exhausting out the bottom of the case, I did it on my test build to try it out and got almost exactly the same temps as when the radiator was mounted on top. The build I'm working on right now has a bottom mounted radiator with exhaust out the bottom. Do not intake into the case, that's adding temperature to the ambient case temps and defeats the purpose of water cooling.
Click to expand...

That doesn't make any sense. Why would it matter if the case air is warm or not? As long as the radiator is getting cool air, it is cooling down the major heat producing components in your system (assuming you are cooling the CPU and GPU). The air temperature inside the case has no effect on the heat transfer of the water blocks, so it really shouldn't matter much, if at all.
 
Dark Ember said:
That doesn't make any sense. Why would it matter if the case air is warm or not? As long as the radiator is getting cool air, it is cooling down the major heat producing components in your system (assuming you are cooling the CPU and GPU). The air temperature inside the case has no effect on the heat transfer of the water blocks, so it really shouldn't matter much, if at all.
Click to expand...

I think he was more referring to heating up the components not cooled by the water (northbridge, memory, hard drives). Heat means shorter life and there is alot of components in a case.

But i have never owned a wc setup and dont know how much heat is outputed from a rad.
 
I was thinking about doing this too, since the bottom of the case provides the most room for components. I had the thought of bringing in cooler outside air through the rad on the bottom then making some sort of duct leading from the bottom, to the top of the case for exhaust, preventing the hot air from escaping into the case. Just an idea
 
Aku12 said:
I think he was more referring to heating up the components not cooled by the water (northbridge, memory, hard drives). Heat means shorter life and there is alot of components in a case.

But i have never owned a wc setup and dont know how much heat is outputed from a rad.
Click to expand...

I understand what he meant. But think about it - you are dissipating the same amount of heat energy with air cooling as you would be with water. Therefore putting that same amount of heat into your case (along with regular ventilation, i.e. exhaust fans) shouldn't really make a difference.

Yes, by making sure the heat blows out you can minimize the hot air in your case. I'm just saying that this doesn't matter all that much because the most heat sensitive parts are in the watercooling loop.
 
Dark Ember said:
I understand what he meant. But think about it - you are dissipating the same amount of heat energy with air cooling as you would be with water. Therefore putting that same amount of heat into your case (along with regular ventilation, i.e. exhaust fans) shouldn't really make a difference.

Yes, by making sure the heat blows out you can minimize the hot air in your case. I'm just saying that this doesn't matter all that much because the most heat sensitive parts are in the watercooling loop.
Click to expand...

True enough. Adding the extra heat generated by the radiator/heat exchanger back into the case is probably not going to cause system instability (on it's own) or any other signifigant problems. Afterall, if you've got a mess of active heatsinks on the CPU and GPU in a "standard" case all they're doing is blowing that heat around in the case to be exhausted with the heat from all the other components.

However, one signifigant advantage of water cooling is selecting where the heat is exhausted. By removing the heat from the CPU and GPU from the internal case temperatures a regular active heatsink on the northbridge will be slightly more effective. In thoery (although I've never tested it) passive RAMsinks on the video card and system memory will also be more effective with the lowered internal temperature. It's also possible that even the HDDs will benefit from the lowered internal temperatures.

It's somewhat self-defeating (IMHO) to invest the money to water cool your computer and not take advantage of all the benefits it offers.
 
Bepunk said:
So you will be sucking air from below your case, and exhausting it into your case?
Click to expand...

Yes...Just like all the people that have their rad's at the front of their case, pulling air through them into it. That seems fairly common...
 
Well, now I'm confused...a LOT of the water cooling setups I've seen had air being pulled through a radiator mounted in the front of the case...would that be any different than pulling it in through the bottom?? Or am I just mistaken, and are people actually venting *out* the front of their case much of the time?

As far as general air-flow goes, my plan was something like:

120mm fan front - in
radiator bottom - in

120mm fan rear - out
PSU rear - out

And maybe an extra just "vent" to alleviate any air pressure problems (I am worried about maybe pulling too much in and not being able to push enough out?...but folks have said this is unlikely to be a problem?...)

That seems to me like it would give a decent air flow from the front/bottom to the top/rear, no?
 
Aku12 said:
I think he was more referring to heating up the components not cooled by the water (northbridge, memory, hard drives). Heat means shorter life and there is alot of components in a case.

But i have never owned a wc setup and dont know how much heat is outputed from a rad.
Click to expand...


1) Bottom mounting advantages will be noise reduction.
2) Coolest point in your case as heat travels up in general.
3) Decently cooled radiator will be only pumping air about 1-2c above ambient temp. It REALLY isn't bad. In fact, in most of case designs, this will cool critical comopnents such as GPU and northbridge better than general case flow due to orientation and heat trapping ability of such case.
4) It leaks, no biggy. Most common component in loop to leak would be reservoir, radiator than whatever...

Cons: You do need a way to make about 2.5-3" height of something. 2.5" casters usually do good on this... actually could be pro on moving case around :p
Most of time, dust will be getting into case at much faster rate than front intake... You will need to clean it up periodically.
more exhaust will be better in your case than intake as it will help radiator fan's to pull air against restriction better -> Found this out with some custom made case testing I've done few months back.
 
The reason i thought mounting a rad at the bottom is bad is if i blow in air my small 80mm fans cant blow out all air. And the diffrent to have it at the bottom or front is no diffrent at all.
My self i have it on the bottom and the air is not blow in or out, its blown around, I havn't cut the holes yet and it works perfect as it is. But it will get better if you cut holes!
 
So in the same way, mounting a radiator to the top of a case, fans on the outside, pulling out (case air moving through the radiator as it's exhausted) is a bad idea? Pushing outside air into the case (whether from top or bottom) is the best way?
 
Yes, outside air into case is the best way. You get the coolest air possible through the radiator, and then you only get a 1-2C rise in case over ambient. That is ALOT better than air cooling.
 
Bepunk said:
Yes, outside air into case is the best way. You get the coolest air possible through the radiator, and then you only get a 1-2C rise in case over ambient. That is ALOT better than air cooling.
Click to expand...

And while I think you are correct, others above in this very thread would apparently disagree with you...heh. :)
 
jinu117 said:
1) Bottom mounting advantages will be noise reduction.
2) Coolest point in your case as heat travels up in general.
3) Decently cooled radiator will be only pumping air about 1-2c above ambient temp. It REALLY isn't bad. In fact, in most of case designs, this will cool critical comopnents such as GPU and northbridge better than general case flow due to orientation and heat trapping ability of such case.
4) It leaks, no biggy. Most common component in loop to leak would be reservoir, radiator than whatever...

Cons: You do need a way to make about 2.5-3" height of something. 2.5" casters usually do good on this... actually could be pro on moving case around :p
Most of time, dust will be getting into case at much faster rate than front intake... You will need to clean it up periodically.
more exhaust will be better in your case than intake as it will help radiator fan's to pull air against restriction better -> Found this out with some custom made case testing I've done few months back.
Click to expand...

Thanks!...this is exactly the sort of stuff I was thinking, too...

A couple things:

1) The height -- yeah, need to figure something out here...I was just thinking of doing casters myself, but if what Cathar said is true, I might want another centimeter or two of clearance...so maybe some casters w/ some sort of "buffer" in between them and the case to boost an extra centimeter to make it a good 6...Of course, I can also just get big ol' "chair" casters or similar from Home Depot or something...hehe.

2) Air flow out -- so you *did* find that to a problem, huh?....hurm....I'm afraid I might need to add another exit fan then, despite really not wanting to. I was hoping to be able to keep fans from off of the sides of top of my case...but sounds like I might need a top blow-hole or something...sigh. I don't mind a vent, but I just hate to keep adding noise-makers. :)
 
I have tried the low mounted radiator thing before and it worked, for a while. I warn those with pets however that pet hair is a definite impediment to cooling

I have three Persian cats……….so I try to keep anything that intakes air as high as possible.

Just a thought ;)
 
Bio-Hazard said:
The old stand-by.......McMaster-Carr............... :eek:
Click to expand...

Heh...indeed, just checked, and they have exactly what I'd want... :)
 
BillR said:
I have tried the low mounted radiator thing before and it worked, for a while. I warn those with pets however that pet hair is a definite impediment to cooling

I have three Persian cats……….so I try to keep anything that intakes air as high as possible.

Just a thought ;)
Click to expand...

Well, I wanted to try to find some of that washable foam dust screen and just mount it along the bottom so it would be foam -> rad -> fans....

Anyone know where I could find a single strip of that foam material though?...I really don't want to get two seperate fan screens and create even more of a dead spot in the rad...heh.
 
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