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Old 03-24-2019, 10:36 PM
System_Engineer System_Engineer is offline
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Default Front Intake vs. Top Exhaust

I have an Obsidian 500D SE RGB case and am wondering which is better:

1) Front mounted H150i Pro RGB that has 3 fans forcing hot air into the case through the radiator.


2) Top mounted H100i RGB that has 2 fans exhausting hot air out of the case through the radiator.

This is perplexing me and it seems that option #2 is more effective.
I would appreciate any wisdom I can get on this matter.

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Old 03-24-2019, 11:07 PM
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That's a tough one and often it's a "consulting answer" ... it depends.

Having the radiator as intake it the best scenario for coolant temperature. The coolest possible air available is going through the fins. This keeps the radiator ... cooler. Now, the radiator exhaust isn't necessarily going to be as warm as you think - perhaps 1-2C higher than the coolant temperature. This isn't going to be anywhere near as high as the CPU temperature ... but you'll likely looking at somewhere from 6-10C or so above ambient, depending on processor.

Now - that does warm up the inside of the case. Keeping the case internal temperature lower is a major advantage of having the radiator as exhaust. However, in this scenario, you can run into challenges ensuring that the radiator gets cool air. We've seen (and I've experienced, personally) cases where GPU waste heat actually winds up impacting (negatively) coolant temperatures, effectively warming the coolant ... and modern, high-end GPUs put off A LOT of heat. So you need to be cognizant of that and manage the heat from the GPU. There are several strategies for doing this; the most common of these is to actually flip the rear fan and have that as intake. I did this in a previous build and based the speed of this fan on a sensor just below the radiator intake. Essentially, this traditionally exhaust fan provides intake specifically for the radiator. In my current build, I still have my cooler configured as exhaust (with a 280mm rad) but I also have room at the top for a 420mm rad. So I have my radiator mounted forward and rear and top rear as exhaust. Using the Commander Pro, I control these fans based in the "Upper Case" temp (the sensor is just over the pump head) and use these exhaust fans to pull the warm GPU waste heat away from the radiator. I also have a temp prop in the intake flow for the radiator so I can confirm that this is actually working pretty well.
Either way ... it's a matter of trial and error. Keep an open mind. Try different things, even if it means bucking the "typical installation". And keep in mind that it's all about managing the flow of heat in the system.
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Last edited by DevBiker; 03-24-2019 at 11:34 PM.
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Old 03-24-2019, 11:31 PM
System_Engineer System_Engineer is offline
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Phenomenal explanation...Thanks again.

I understand completely and am going to do some playing around as you suggested.

(Thermodynamics + Fluids + Energy) = (Money + Time) = Enjoyable Challenges!

Have a good one.
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Old 03-25-2019, 06:23 AM
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It depends what works best on your setup, really.

In my Case, the front-mounted H115i RGB Platinum works better when mounted in the front with fans as intake. The coolant temperatures and thus the CPU temperatures are considerably cooler under full load/stress testing that way. The case temperature doesn't warm up all that much with the front intake either, maybe ~1°C more, component temperatures (video cards, VRMs, Chipset, etc.) don't seem to be affected significantly either. Note that I have a push/pull configuration, though, without the additional pull fans the air isn't propelled through the radiator and the case as quickly and causes more heat to linger which does raise the case temperatures a bit more.

That said, I'd recommend going with a 360mm Radiator if it fits your case (it didn't fit mine without cutting out some stuff so I went for the 280), the larger surface area on the radiator should help quite a bit and you should be able to run the fans with less speed if desired.

Last edited by Glzmo; 03-26-2019 at 02:21 AM.
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Old 03-25-2019, 04:50 PM
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In terms of straight benchmarking and lowest possible temperatures, the front intake installation will usually come out a few degrees ahead. A definite portion of that is local temperature (front rail is cooler than top 2-3 inches of the case). However, in this instance the mounting location requires a compromise on size and this is often the more meaningful factor. A H100i Pro/Platinum 240mm is perfectly capable of cooling a 9700K. However, it may require higher fan speeds to do so. A 360mm H150i has 50% more surface area and can disperse the same wattage with a lot less fan speed. Your use is likely not affected by a CPU/coolant temperature change of +-2C in either direction. Getting to use 1000 rpm on the cooler instead of 1600 rpm is going to be a lot more noticeable in day to day use. Some people are immune to fan noise. For others it cuts like a knife. Either way, the placement and size option is probably the more logical basis of deciding.
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Old 03-28-2019, 10:15 AM
D34DMetalPC D34DMetalPC is offline
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I've got my C700M set up with intake from the front and intake from the top. The 280mm rad is also up front as intake. Then there is one exhaust fan at the back (9 140mm fans in total!!!). I have to agree with everyone else about having the rad as intake rather than exhaust, but really it is up to the builder!
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h110i, h150i pro, obsidian 500d se

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