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CPU>GPU>Radiator or GPU>CPU>Radiator ?

Gepo32

New member
I'm planning a build in an NCASE M1 (mini-ITX), so only room for one 240mm radiator and an Icebear LT Solo. I have a Coffee Lake i7-8700K and an AMD Radeon 5700 XT. I have no idea what will produce the most heat, so I need some advice on which order I should build my loop.

Should I do CPU>GPU>Radiator of should I do GPU>CPU>Radiator ?
Additional question: I'm actually thinking of underclocking both CPU and GPU, but would overclocking CPU of GPU or both change the order of my loop?
 

Metropolis34

Support
Staff member
Additional question: I'm actually thinking of underclocking both CPU and GPU, but would overclocking CPU of GPU or both change the order of my loop?
Sorry dude i do not get this question. What do you want to do over or under clock? The Eisbaer Solo would not be enough to cool the components with a 240 mm radiator. I mean it can cool of course but you would not have the ideal temperatures.
 

Gepo32

New member
Ah ok, did not think about not having enough radiator to cool overclocking.

Still, in what order should I make my loop? GPU to CPU or CPU to GPU ? If the GPU does not get very hot maybe it would be better to put it before the CPU. Or does this not matter in a very small loop? (and thank you for answering so fast!)
 

Gepo32

New member
I mean ideally you would do: Radiator>CPU>Radiator>GPU, but I can only install one radiator, so I will have warm water running from the CPU to the GPU (or other way). Does is make a difference ?

Ok, maybe the question is a bit silly, just want to make sure I don't do anything stupid before I buy my stuff :p
 

Metropolis34

Support
Staff member
How big is the radiator that you want to use in your system? In my system is the setup as follows : CPU -> GPU -> Radiator and reservoir combo back to CPU. If you have powerfull components in your system i would advise to go from reservoir to CPU and then to the first radiator and after GPU and a second radiator which goes back to reservoir. By the current hardware today more radiator surface is usefull i think ^^
 

Thunderchild

New member
GPU's make more heat. My RX 5500 XT is using up to 120W when running folding at home, my CPU is 65W, rarely CPU's go over 100W. I think GPU's are supposed to be allowed to get hotter so you want to send coolant to the CPU first as it's speed is more temperature dependent and then the GPU. Looking at the location of my quick couplings, if i was to split them and put a GPU block in it would mean the GPU would come after the CPU.
 

twinprime

New member
When both are on custom water, I seriously doubt GPU generate more heat. In my system the 2080Ti is on a Alphacool waterblock and idle 25C with max load at 37C (30min at 100% GPU load). CPU 3900X idles at around 38C and goes up to 67C during 30min max load. All stock clocks.

If you uses a decent custom loop with enough rads (I'm running a 65cmx360mm and a 45cmx420mm). Jayz2Cent has proved that loop order doesn't really matter, difference maybe 1 degree. It's because when the loop is in its steady state the water moves through it so fast that the temperature across your whole loop will be very similar,
 

Thunderchild

New member
You confuse heat and temperature. Heat is energy, energy out is broadly energy in. My RX 5500 XT is 120W, my CPU is 65W, my GPU makes more heat therefor. What temperature you can cool to is a different matter. If you have two identical GPU's or CPU's and run them on an identical load and then give one a larger radiator the GPU/CPU will be cooler despite the same power consumption, it is not making less heat, the heat energy is just diluted into more coolant and more easily dumped by the larger radiator.
 

twinprime

New member
In the world of cooling, the wattages and theories are mostly useless because it's much quicker to get emperical with this stuff (and more fun to)?
The question that was asked was "which generate more heat." I believe they actually mean which actually runs hotter in their setup. Who cares if CPU actually generates 50% less heat than GPU if it's half as cool in the same loop? How cool, or hot the component runs is ALL that matters regarding cooling.

My RX 5500 XT is 120W, my CPU is 65W, my GPU makes more heat therefor. <--- sure, let's assume that's correct for a second (it's most likely would be correct) but your GPU when on water will be half as cool as your CPU on the same water. From that point which will you try to cool more? Your GPU because it "makes more heat," or try to cool your CPU because it's simply hotter?
 

Thunderchild

New member
Try telling my employer that, they only make radiators. I can assure you that when you have an engine rejecting 100kWh of heat that must not go over a certain temperature with radiators of 2 square meters and 200mm deep you don't just guess. Thermo physics are fairly well understood and not that complicated. As much as you PC enthusiasts may think all of this gear is cutting edge it's actually childs play and there is not much you can do wrong. The radiators used are similar to what we use as car heaters that I expect deliver several hundred watts of heat output when you run 80-90C coolant through them. I can also assure you they are not worth the extortionate rices you pay. You are buying convenience not performance.

You can mix terms up and ignore stuff but you still can't answer the question if you do. The rate the cooling block can transfer heat to the coolant will be relevant. Given the same coolant temperature for both GPU and CPU you will get a certain amount of temperature rise per watt of heat output. if the cooling blacks have the same transfer characteristics they will be at the same temperature. If one block performs less than the other then the item will get warmer as it takes more temperature difference to drive heat energy from the GPU to the water, this will generally be down to surface area. Add to that that the water usually goes to the CPU first so the water the GPU see's will already be warmer so the GPU may remain warmer for the same heat output.

In the world of cooling, the wattages and theories are mostly useless because it's much quicker to get emperical with this stuff (and more fun to)?
The question that was asked was "which generate more heat." I believe they actually mean which actually runs hotter in their setup. Who cares if CPU actually generates 50% less heat than GPU if it's half as cool in the same loop? How cool, or hot the component runs is ALL that matters regarding cooling.

My RX 5500 XT is 120W, my CPU is 65W, my GPU makes more heat therefor. <--- sure, let's assume that's correct for a second (it's most likely would be correct) but your GPU when on water will be half as cool as your CPU on the same water. From that point which will you try to cool more? Your GPU because it "makes more heat," or try to cool your CPU because it's simply hotter?
 

Eddy

Iceman
Staff member
Without going into physical details.... it doesnt really matter here if you go like: CPU - Rad - GPU or CPU -GPU - Rad or GPU - Rad - CPU.
And one 240 mm radiator for OC with our components.... is possible.... but only with high rpm fans.
 

Thunderchild

New member
the bigger problem we face with PC cooling is that the colder the components the better but there will always be a difference on ambient so the same parts that would reject a lot more heat from 90C coolant allow less heat rejection since 90-25 is a bigger number than 50-25. I find that on my CPU only system the speed of the pump is irrelevant as I can bring lots of warm water or a little cool water, the net cooling is the same, so 20% or 100% pump speed same thing. i will guess that with more that one item being cooled by the loop speeding the pump up make sense as it means the faster flowing water will heat up by less as it goes through the first item so that it is still cool enough to be good for the second item.

I have the heat exchanger from my 35kWh gas boiler that I want to add to my loop, it will do far less than that as 35kW is to heat water to 60C with 100's C of gas flame but I am sure that it will make a decent cooler.

Currently there is not much point in doing that as my 2x140mm fan radiator is plenty for my CPU and I don't see any water blocks for my RX 5500 XT available so looks like I am stuck with air on that.
 

twinprime

New member
You keep missing the point that the question here is which is hotter, and therefore requries more attention.

Fact: When both are on decent water blocks, using the same coolant and pump, same loop, the CPU will always be way hotter than the GPU is, even if the GPU consumes more power. Obviously the CPU requires more attention regarding cooling (EVEN if it consumes less energy i.e. "generate less heat" per your assertion). Use your numbers and scientific facts to dispute this fact.
Fact (most likely): CPU consumes less power thaN GPU so generate less heat than GPU. This is probably true. But seriously who cares if it generates less heat if it's HOTTER?
 

Thunderchild

New member
Well it's a toss up that you have to decide. From what I see GPU's normally run hot, my air cooled GPU runs at near 90C normally but my CPU on air cooling would not go above 60C. A well cooled CPU will auto overclock more so you may want to get the most out of that knowing that the GPU will run fine a bit hotter. The best thing you can do is set it up and see what difference the pump speed makes. Pumping faster will give the coolant less time to heat up so both GPU and CPU will see about the same coolant temperature.
 
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