[SOLVED] Proper Air cooling for new PC

[dragonfly22588]

Ok, so I'm building a new system and I want to ensure this time around I build something that cools the system properly and doesn't accumulate a lot of dust. My old system which is a mess inside always got a lot of dust. This is my proposed new setup below, nothing fancy and it's all air cooled but the question is what is the ideal number and placement of the exhaust fans? The Fractal case comes with 2 x 140 mm Aspect fans and I was planning to use the 2 x 120 mm exhaust fans I have on my current system to put 1 in the back and 1 on top. This is in addition to my CPU cooler fan. I read somewhere that if I'm taking more in then exhausting, it can cause negative air flow and lead to more dust. Given my setup, what is the optimum fan setup and type to use? Thanks.

PCPartPicker Part List: https://pcpartpicker.com/list/bLQZ3y

CPU: Intel Core i5-12400F 2.5 GHz 6-Core Processor ($166.99 @ B&H)
CPU Cooler: Thermalright Assassin X 120 Refined SE 66.17 CFM CPU Cooler ($21.63 @ Amazon)
Motherboard: MSI PRO B660M-A WIFI DDR4 Micro ATX LGA1700 Motherboard ($149.99 @ B&H)
Memory: Silicon Power GAMING 32 GB (2 x 16 GB) DDR4-3200 CL16 Memory ($68.47 @ Newegg Sellers)
Storage: Samsung 970 Evo Plus 2 TB M.2-2280 PCIe 3.0 X4 NVME Solid State Drive ($159.99 @ Adorama)
Video Card: ASRock Challenger D Radeon RX 6600 8 GB Video Card ($239.24 @ Newegg)
Case: Fractal Design Focus 2 ATX Mid Tower Case ($69.79 @ Newegg)
Power Supply: Corsair RM650 650 W 80+ Gold Certified Fully Modular ATX Power Supply ($92.43 @ Amazon)
Monitor: Asus VG245H 24.0" 1920 x 1080 75 Hz Monitor (Purchased For $0.00)
Total: $968.53

 

[geofelt]

A very nice build list, do not change a thing.

As to cooling, two front 140mm intakes is all you need.
Use only a single 120mm rear exhaust fan to direct the airflow past the cpu cooler and the graphics card.
Adding top exhausts might increase the front intake volume a bit, but they would also redirect the airflow up to the top before it can cool the cpu, gpu and motherboard. Strong exhaust fans will also tend to draw in unfiltered air from adjacent openings.
In theory, at least if all the intake air is from one source and is filtered, that will keep your parts cleaner.


Your parts are not unusually hot. I would not be worried at all.

 

[Paperdoc]

I'd go with your plan of using both old 120mm fans, one rear and one top, as exhaust. In terms of air flow a balance, 140 mm fans typically will generate more air flow than 120 mm models for the same fan speed signal, so it is likely that you will have small positive pressure inside your case. Now, the dust filter on the intake fans will reduce their air flow slightly, but still they likely will out-perform the 120 mm units. Normally you do not have dust filters on exhaust fans, but your case has a single filter cover for both of the top locations, and there may be no way to NOT have that filter over the top exhaust. Not a real problem, only a minor reduction in exhaust air flow there.

The top has two positions - rear, and middle of the case. I'd suggest the rear position just above the CPU location. II would worry that a fan in the top middle location would "steal" air flow from the front of the CPU cooler which should be blowing towards the case rear fan.

The two 140 mm fan supplied with the case are specified as 3-pin fans. For speed control such fans require that their mobo header be configured correctly to use the older Voltage Control Mode (aka DC Mode), and not PWM Mode. According to your mobo manual both of its SYS_FAN headers arrive pre-configured that way, but you can change them if you are using a 4-pin fan.

You have not told us what your older 120 mm fans are - 3-pin or 4-pin. I suggest you connect those two to one of the SYS_FAN headers and set that header's Mode to DC for 3-pin fans, or PWM for 4-pin. Connect the front pair to the other and set its Mode. When first setting up, configure each of them to use the default Standard Profile for automatic speed control. AFTER you have it all operating you can experiment if you wish to ensure the air balance is set to produce the small internal positive pressure that can prevent influx of unfiltered air at cracks in the case. For this you need a small source of smoke - a smouldering cigarette or incense stick. With the system running, move the smoke source slowly over the case exterior near any small cracks or openings and observe which way the smoke moves. If it drifts away from the case the air is blowing out of the cracks and you are in good shape! If it is sucked in, room air is flowing in at the cracks. If it moves very fast, there is a larger-than-needed pressure difference. Do this process for two or three workload scenarios to you can test the full range of possible uses.

IF you feel the air flow balance is wrong, you can go into BIOS Setup for the fan pair you want to adjust. Change its Profile setting so that you can specify your own custom "fan curve" of fan speed versus temperature. You can adjust one set to either increase or decrease its impact on case air flow to achieve a better balance. Remember to go through the Exit Menu to Save and Reboot.

 

[dragonfly22588]

@Paperdoc Thank you for your very thorough answer. I did recently read a little into the positive and negative airflow outcomes within a case and it appears the general consensus is a positive airflow is what will keep dust out. With that said I did find out the front Aspect case fans have a CFM of 41 each so 82 total. My rear exhaust fan is a Be Quiet Pure Wings2 120 mm PWM high speed https://www.bequiet.com/en/casefans/1635 generating 65.51 CFM @ 100% PWM. I do not know what the top exhaust fan generates. With that said it seems I would benefit with a 120 mm up top or possibly a single 140 mm to generate more than plenty positive air flow. I could get another Be Quiet fan. If I do what is the ideal net positive CFM I should have in the case? Does the CPU fan add anything to the exhausting CFM? The top filter can technically be removed but I'd like to keep it there, again to prevent dust from coming in.

Is it ok to have a top 140, rear 120? If I get another Aspect 140 or a brand I can identify the CFM then I can be reasonable sure of having a higher total exhaust CFM. Does that all seem correct?

 

[geofelt]

Changing cooling fan arrangement is usually fairly easy.
My advice is to set up simply with what you have and see how you do.
If you find you have a cooling issue or if you simply want more cooling, then you have a base line to compare to.
Use the simple CPU-Z stress test to load all cores.
Run HWmonitor while you are testing.
It will give you the current, minimum, and maximum temperatures of the individual cores. If you see the max on a core of 100c. in red, it means that core throttled. Do not be alarmed if you keep running. It simply means that that core was slowed down, likely only for a moment.
Cooling is important for the graphics card.
Run a graphics stress test. Graphics cards will target 80c. and perform the best they can keeping that temperature.

 

[Paperdoc]

OP, you seem confused about the air flow balance. And remember, what goes in must come out. Do we start out with POTENTIAL air flow numbers, but the REAL air flow in MUST be the same as out. What DOES change is the PRESSURE difference between the exterior and interior of the case. Without a driver like a fan, air flows from the higher-pressure zone to lower. So at small openings or cracks the air will flow OUT of your case (and prevent dust intake) if the pressure inside is higher than out. Now reverse that view, and consider HOW the pressure inside can become higher? It can happen if the INTAKE fans are able to try to push air MORE than the exhaust fans. So we try to arrange that the max POTENTIAL air flow for INTAKE is higher than the max potential exhaust flow. In that sentence, substitute "rated" for "Potential" and you get the idea.

You say you have INTAKE at front rated for 82 CFM max, and EXHAUST at rear rated for 65.5 CFM. Adding a single 120 mm top fan as exhaust adds at least 40 CFM to the exhaust capacity, so you're already exceeding the intake max capacity and causing negative internal pressure. Going to an even larger top fan makes that worse. Adding that 120mm top fan is a good idea. AFTER you have that done and working, use the air flow smoke tracing technique to determine which way air is flowing at cracks, and adjust the exhaust fan speed downwards if necessary to ensure the smoke flows AWAY from the case.

 

[dragonfly22588]

@Paperdoc Thanks, I realized after I posted that I mixed up the positive and negative airflow meaning but now I understand. I will do as you suggest. I can't tell but with my motherboard do I have the pins to be able to use my PWM rear 120 and control the fan speed while using my old case 120 mm 3 pin and control it by voltage?

 

[Paperdoc]

First, thanks for Best Solution.

No problems controlling the fans - I believe you have two 140 mm 3-pin fans supplied with the case fro the front. Then two older fans 120 mm - are these both 4-pin type?

The key thing here is to group your fans according to the type, so PWM 4-pin fans in one group, and 3-pin Voltage Controlled fans in another. Use a simple Splitter for each group, like this

https://www.amazon.com/Cable-Matters-2-Pack-Way-Splitter/dp/B07PXLHNZ6/ref=sr_1_3?crid=3F8I8UZMTHYBH&keywords=fan+splitter&qid=1672377525&sprefix=fan+splitter,aps,91&sr=8-3

That is a 2-pack of 4-pin Splitters, but you can use that for both 3- and 4-pin fans. They have 3 output arms but you only need two I think. Just be sure with each Splitter group to plug one fan into the single output arm that has ALL 4 pins in it - that is the only output that will send its fan's speed signal back to the mobo header.

Your mobo has four fan headers in total. One is CPU_FAN1 for the CPU cooler. One is PUMP_FAN1 you do NOT need to use - it is mainly for the pump of a liquid-cooled system. There are two SYS_FAN headers at rear and bottom, so use one of these for each of the two fan groups. The manual does NOT tell you an important feature you will need to adjust in BIOS Setup. Every fan header has a screen for adjusting its operating settings, and one of these is the MODE, which is adjusted to match the type of fan attached to that header. Your mobo comes with both SYS_FAN headers pre-set to the older Voltage Control Mode (aka DC Mode). When you connect the two 3-pin fans using a Splitter to one SYS_FAN header, you can leave that alone. But for the two 4-pin fans and their Splitter, set that header to PWM Mode. That way each fan type gets its optimum signal set for good control.

 

[dragonfly22588]

@Paperdoc Yes, the front fans are 3 pins and they appear like they can connect to each other allowing me to use a single SYS_Fan plug for these fans. My rear exhaust fan is the 120 mm 4 pin PWM however upon closer inspection it seems that my top exhaust is a 3 pin 140 mm fan with a switch to toggle "L" or "H" fan speed. In that case can I attach the rear exhaust PWM fan to the other SYS_Fan and the 3 pin top exhaust to the PUMP_FAN1 without the need to purchase anything else? Then it sounds like I can set the proper power setting for each fan right?

 

[Paperdoc]

OK, for that 3-pin 140 mm top fan, using the PUMP_FAN1 header is probably right. (The problem here is that the manual does not tell us things.) MOST PUMP_FAN headers have the same configuration options as other headers, but include an extra to choose whether you have connected to that header a fan or a pump. Set that to FAN so it allows you to use its speed control ability. Set it to Voltage (or DC) Mode for the 3-pin fan, and use the Standard automatic speed control Profile. If there is a choice of TEMPERATURE sensors for it to use, set that to the motherboard, not the sensor inside the CPU chip. If you adjust this way, that header will deal with the top fan exactly as any other common SYS_FAN header would.

On the fan itself, set that switch to H for high speed. This will allow the header to control its speed properly. The L is only for use when you have NO way to control its speed and want it running more slowly all the time.