CPU Cooler and Top Exhaust Fan Airflow Question

LukeMurtagh1995 · 21 Jan 2019 at 17:21

Hello everyone,

I had a quick question and wondered if anyone more experienced than I could help. I was planning on building my new PC with an air cooled Corsair 780t case. My plan for cooling was to have three Noctua NF-S12A 120mm fans at the front and one same fan at the bottom for intake, and one NF-A14 140mm fan at the rear and two more of the same fans at the top for my exhausts. I am also going with a NH-D15 CPU cooler which will blow towards the rear exhaust fan. Could the top two 140mm exhausts interfere with the airflow to my CPU cooler? I can’t imagine the top rear fan would, as that should just help to exhaust hot air from my CPU cooler, but wouldn’t the top middle fan just end up exhausting cool air out of my case that otherwise would have entered my CPU cooler?

TLDR: Do top exhaust fans interfere with airflow to a CPU air cooler?
Thanks for the help!

Edit:
My build:
CPU: i7-9700K
CPU Cooler: Noctua NH-D15
Motherboard: Asus ROG Maximus XI (WiFi)
Memory: Corsair Vengeance LPX 16GB (2x8GB) DDR 4 3200MHz
GPU: EVGA Superclocked 1080 8GB
Storage: x2 970 EVO 1 TB SSD
PSU: Corsair RMX 650W
Case: Corsair 780t
Case Fans: x4 NF-S12A x3 NF-A14.

LuckyBenski · 22 Jan 2019 at 07:53

I'd say 7 case fans is potentially excessive. It's good that you have the space but I'd try putting 2-3 intake fans in, then possibly just one exhaust. Positive pressure in the case is generally a good thing.

Having intake and exhaust fans very close together can cause air recirculation or for fresh air to be exhausted rather than "used" by a heatsink. So I would advise not having any exhaust fans in front of or above the CPU cooler. Anything in front can supply fresh air, anything behind can remove warm air.

I'd also consider the usefulness of empty fan slots for similar reasons. Will an open slot between the front panel and the CPU cooler just release air that would otherwise flow directly to the cooler? Possibly try covering those with cardboard to encourage front--to-back airflow. If it works well you can find a more aesthetically pleasing solution.

Experimentation with your particular case, cooler and other hardware will ultimately tell you the answer

doyll · 22 Jan 2019 at 13:53

LukeMurtagh1995 said:
Hello everyone,

I had a quick question and wondered if anyone more experienced than I could help. I was planning on building my new PC with an air cooled Corsair 780t case. My plan for cooling was to have three Noctua NF-S12A 120mm fans at the front and one same fan at the bottom for intake, and one NF-A14 140mm fan at the rear and two more of the same fans at the top for my exhausts. I am also going with a NH-D15 CPU cooler which will blow towards the rear exhaust fan. Could the top two 140mm exhausts interfere with the airflow to my CPU cooler? I can’t imagine the top rear fan would, as that should just help to exhaust hot air from my CPU cooler, but wouldn’t the top middle fan just end up exhausting cool air out of my case that otherwise would have entered my CPU cooler?

TLDR: Do top exhaust fans interfere with airflow to a CPU air cooler?
Thanks for the help!

Edit:
My build:
CPU: i7-9700K
CPU Cooler: Noctua NH-D15
Motherboard: Asus ROG Maximus XI (WiFi)
Memory: Corsair Vengeance LPX 16GB (2x8GB) DDR 4 3200MHz
GPU: EVGA Superclocked 1080 8GB
Storage: x2 970 EVO 1 TB SSD
PSU: Corsair RMX 650W
Case: Corsair 780t
Case Fans: x4 NF-S12A x3 NF-A14.

Yes, top fans will interfere with case airflow. We want good front to back flow. Best way in most cases is something like NF-A14 as front and bottom intakes. NF-A12S are not good because they do not have a high enough static pressure rating to overcome grill and filter restriction except at or near full speed. Remove all unused PCIe back slot covers to increase rear vent area around GPU. Have bottom intake fans speed synced with GPU fans and front intakes speed synced with CPU fans.

A bit of FYI; 2x 140mm fans move same amount of air as 3x 120mm fans of similar design and 2x 140mm fans are quieter too.

You might find link below to basic guilde of how airflow works and how to optimize case airflow of interest.
https://forums.overclockers.co.uk/t...-i-put-my-temp-sensor.18564223/#post-26159770

LukeMurtagh1995 · 22 Jan 2019 at 14:14

doyll said:
Yes, top fans will interfere with case airflow. We want good front to back flow. Best way in most cases is something like NF-A14 as front and bottom intakes. NF-A12S are not good because they do not have a high enough static pressure rating to overcome grill and filter restriction except at or near full speed. Remove all unused PCIe back slot covers to increase rear vent area around GPU. Have bottom intake fans speed synced with GPU fans and front intakes speed synced with CPU fans.

A bit of FYI; 2x 140mm fans move same amount of air as 3x 120mm fans of similar design and 2x 140mm fans are quieter too.

You might find link below to basic guilde of how airflow works and how to optimize case airflow of interest.
https://forums.overclockers.co.uk/t...-i-put-my-temp-sensor.18564223/#post-26159770

Thanks for the reply. I had thought about getting just two 140mm fans at the front instead of three 120mm fans, but I thought three 120mms would give me a more thorough airflow as they will be pulling air into more of my case, although I don’t know how much of a benefit a more equal airflow will have on temperature. Would you happen to know which type of NF-A14 fan would be best? There are just the generic NF-A14 fans but I also see industrial variants which can run to around 3000 rpm, albeit at a significant increase in noise. Would the industrial fans be overkill?

Edit: I’ve also just seen what you’ve linked me. I’ve already decided to go with one SSD and one NVMe SSD so I won’t need my hard drive cages as in my case they sit right in front of my front intake fans. I’ll also ensure to remove unused PCIe back slot covers as you suggested originally. I realise I may sound paranoid about making sure my temperature are low but I have heard that many first-time builders can negelect airflow so I’m trying (perhaps too hard) to try and make sure I don’t make the same mistake.

LukeMurtagh1995 · 22 Jan 2019 at 14:16

LuckyBenski said:
I'd say 7 case fans is potentially excessive. It's good that you have the space but I'd try putting 2-3 intake fans in, then possibly just one exhaust. Positive pressure in the case is generally a good thing.

Having intake and exhaust fans very close together can cause air recirculation or for fresh air to be exhausted rather than "used" by a heatsink. So I would advise not having any exhaust fans in front of or above the CPU cooler. Anything in front can supply fresh air, anything behind can remove warm air.

I'd also consider the usefulness of empty fan slots for similar reasons. Will an open slot between the front panel and the CPU cooler just release air that would otherwise flow directly to the cooler? Possibly try covering those with cardboard to encourage front--to-back airflow. If it works well you can find a more aesthetically pleasing solution.

Experimentation with your particular case, cooler and other hardware will ultimately tell you the answer

Thanks for the help. I might initially try just three 120mm fans at the front and one 140mm fan at the rear.

LukeMurtagh1995 · 22 Jan 2019 at 14:29

LukeMurtagh1995 said:
Thanks for the reply. I had thought about getting just two 140mm fans at the front instead of three 120mm fans, but I thought three 120mms would give me a more thorough airflow as they will be pulling air into more of my case, although I don’t know how much of a benefit a more equal airflow will have on temperature. Would you happen to know which type of NF-A14 fan would be best? There are just the generic NF-A14 fans but I also see industrial variants which can run to around 3000 rpm, albeit at a significant increase in noise. Would the industrial fans be overkill? Do you also have any recommendations for 120mm fans? I can find several different Noctua 120mm fans for sale on various websites but if you have any specific one in mind I’d be very interested in hearing your advice.

Edit: I’ve also just seen what you’ve linked me. I’ve already decided to go with one SSD and one NVMe SSD so I won’t need my hard drive cages as in my case they sit right in front of my front intake fans. I’ll also ensure to remove unused PCIe back slot covers as you suggested originally. I realise I may sound paranoid about making sure my temperature are low but I have heard that many first-time builders can negelect airflow so I’m trying (perhaps too hard) to try and make sure I don’t make the same mistake.

Whoops, ignore this post. I made a mistake.

doyll · 22 Jan 2019 at 16:18

LukeMurtagh1995 said:
Thanks for the reply. I had thought about getting just two 140mm fans at the front instead of three 120mm fans, but I thought three 120mms would give me a more thorough airflow as they will be pulling air into more of my case, although I don’t know how much of a benefit a more equal airflow will have on temperature. Would you happen to know which type of NF-A14 fan would be best? There are just the generic NF-A14 fans but I also see industrial variants which can run to around 3000 rpm, albeit at a significant increase in noise. Would the industrial fans be overkill?

Edit: I’ve also just seen what you’ve linked me. I’ve already decided to go with one SSD and one NVMe SSD so I won’t need my hard drive cages as in my case they sit right in front of my front intake fans. I’ll also ensure to remove unused PCIe back slot covers as you suggested originally. I realise I may sound paranoid about making sure my temperature are low but I have heard that many first-time builders can negelect airflow so I’m trying (perhaps too hard) to try and make sure I don’t make the same mistake.

2x 140mm front intakes is enough, but if you can add 1x 140mm bottom intake as well. NF-A14 PWM would work fine. What you are trying to do is to have case fan intake airflow total to be about 40% more than component airflow total.

tamzzy · 22 Jan 2019 at 16:23

LukeMurtagh1995 said:
My plan for cooling was to have three Noctua NF-S12A 120mm fans at the front and one same fan at the bottom for intake, and one NF-A14 140mm fan at the rear and two more of the same fans at the top for my exhausts.

what an absolute waste of money.
3 good fans is usually where the performance/price curve hits the peak - 2 intakes in the front, 1 exhaust in the rear
4 fans if you're OCD and want to waste a bit more money.
7 fans won't help with much more.

LukeMurtagh1995 · 22 Jan 2019 at 16:41

doyll said:
2x 140mm front intakes is enough, but if you can add 1x 140mm bottom intake as well. NF-A14 PWM would work fine. What you are trying to do is to have case fan intake airflow total to be about 40% more than component airflow total.

Right, so I’ll try two 140mm Noctua NF-A14 Industrial 2000 PWMs for my front intake as they have an airflow of 107.41 CFM and a static pressure of just over 4, and one of the same fan for my rear exhaust. In terms of my bottom intake I would have to get a 120mm fan as there isn’t the room for a 140 so I imagine a NF-F12 Industrial 2000 PWM would be good as it has an airflow of 71.69 CFM and a static pressure of just under 4. Is there anything about this setup you would change?

doyll · 22 Jan 2019 at 17:23

tamzzy said:
what an absolute waste of money.
3 good fans is usually where the performance/price curve hits the peak - 2 intakes in the front, 1 exhaust in the rear
4 fans if you're OCD and want to waste a bit more money.
7 fans won't help with much more.

Wow! seems you are in a very bad mood .. and your post doesn't even really address the problems of fans with such low static pressure ratings they cannot supply enough air regardless of how many are being used.

LukeMurtagh1995 said:
Right, so I’ll try two 140mm Noctua NF-A14 Industrial 2000 PWMs for my front intake as they have an airflow of 107.41 CFM and a static pressure of just over 4, and one of the same fan for my rear exhaust. In terms of my bottom intake I would have to get a 120mm fan as there isn’t the room for a 140 so I imagine a NF-F12 Industrial 2000 PWM would be good as it has an airflow of 71.69 CFM and a static pressure of just under 4. Is there anything about this setup you would change?

You don't need industrials. They are not quiet even at low speeds. The normal NF-A14 1500rpm is more than enough .. but do whatever you want.

LukeMurtagh1995 · 22 Jan 2019 at 17:28

doyll said:
Wow! seems you are in a very bad mood .. and your post doesn't even really address the problems of fans with such low static pressure ratings they cannot supply enough air regardless of how many are being used.

You don't need industrials. They are not quiet even at low speeds. The normal NF-A14 1500rpm is more than enough .. but do whatever you want.

Oh, okay. I'll just settle for three 140mm NF-A14 1500rpms then. Thanks for your help!

tamzzy · 22 Jan 2019 at 17:41

doyll said:
Wow! seems you are in a very bad mood

lol. wasn't meant to come across that way

okay i'll put it in another way...
spending £100 on 7 fans won't net OP as big a gain as one would expect, when 3 are sufficient.

doyll said:
and your post doesn't even really address the problems of fans with such low static pressure ratings they cannot supply enough air regardless of how many are being used.

well...

tamzzy said:
3 good fans

it kinda does...

evakaname · 22 Jul 2019 at 16:47

doyll said:
2x 140mm front intakes is enough, but if you can add 1x 140mm bottom intake as well. NF-A14 PWM would work fine. What you are trying to do is to have case fan intake airflow total to be about 40% more than component airflow total.

Hi! I may be out of line here but this is exactly what i was searching for. Im looking around for some tips to my new build too and you seem to know what you are talking about.

I recently got a Noctua NH D15, and a Phanteks Enthoo Pro M (TG) case, but im having trouble deciding on case fans. 3 would be ideal for space and motherboard headers, and also airflow, but i dont know what fans to buy. The CPU cooler can go up to 82 CFM, and ill need to feed that beast, and also take that hot air all out on a workload. So im guessing ill need some beast fans, no? I also have an Asus Geforce RTX 2080.

tamzzy · 22 Jul 2019 at 16:51

evakaname said:
Phanteks Enthoo Pro M

alraedy has a 140mm fan at the rear. keep it there...

2 more of these at the front and all set:
https://www.overclockers.co.uk/arctic-cooling-p14-pwm-pst-black-fan-140mm-fg-04k-ar.html

tamzzy · 22 Jul 2019 at 16:52

evakaname said:
The CPU cooler can go up to 82 CFM, and ill need to feed that beast

it wont blow 82cfm in real world due to the resistance of the d15 cooler

half that, probably.

LuckyBenski · 22 Jul 2019 at 17:55

tamzzy said:
it wont blow 82cfm in real world due to the resistance of the d15 cooler
half that, probably.

Also if you're feeding reasonably cool air to the CPU fans, it probably won't end up running at full speed

tamzzy · 22 Jul 2019 at 17:58

LuckyBenski said:
Also if you're feeding reasonably cool air to the CPU fans, it probably won't end up running at full speed

hah. that too...unless pwm configured wrongly (or not at all)

evakaname · 22 Jul 2019 at 18:09

tamzzy said:
it wont blow 82cfm in real world due to the resistance of the d15 cooler
half that, probably.

LuckyBenski said:
Also if you're feeding reasonably cool air to the CPU fans, it probably won't end up running at full speed

Right, i havent considered that resistance, i assumed it is the overall number lol... though it may take in quite a bit of air at workload, but i can fit two 140 fans on front so that should take care of it.
Im also doing math for max capacity because that should be the point of measure i thought, should it need to go up.

evakaname · 22 Jul 2019 at 18:14

tamzzy said:
hah. that too...unless pwm configured wrongly (or not at all)

Well, i have currently 3 pin fans (two 140s come with the TG edition of this case, and i have some other no name fan as 3rd on front), no pwm though... i thought of setting case fans full speed from bios, just to keep cool and not having to worry about it?

i usually game or digital paint big canvases on that pc The latter not needing that much power besides saving times i know but cant hurt to keep cool, just so i dont need to keep adjusting from bios when i game or work. Noise doesnt bother me much, case is under and front of the table.

tamzzy · 22 Jul 2019 at 18:17

The stock phanteks fans are pretty decent. No need to change them.

Just use the cheap no name fan as the exhaust. And use the 2 phanteks fans (I'm assuming they're both 140mm size) at the front intakes. Sorted.
No need to waste money if not needed.