Question Understanding static pressure / airflow fan details.. NZXT F140P V2 vs. F140Q V2.. which is better for me?

[Dunkz]

I want to install a 140mm rear fan, i have a NZXT H7 flow case and i was looking at a NZXT 140mm fan

I found the NZXT F140P V2 and F140Q V2. the main differences in specs seem to be airflow and pressure

The F140P specialises in Static Pressure, has airflow rated at 93.2 CFM and air pressure rated at 4.45 mm H2O
https://www.scan.co.uk/products/nzxt-f140q-v2-quiet-airflow-fan-white

The F140Q specialises in Airflow/Pressure, has airflow rated at 102.9 CFM and air pressure rated at 1.7 H2O
https://www.scan.co.uk/products/nzxt-f140p-v2-static-pressure-fan-white

I dont understand the relative importance of these details so i cant work out which would be better for my needs. Pls can anyone help explain what the practical implications are of the differences between these fans, and which would act better as a rear exhaust? the H7 Flow case is pretty airy with lots of space so my gut reaction is perhaps i only need the F140Q but i dont understand the implications of the technical details. they are both priced the same so it doesnt seem to be that one fan is better quality than the other.

any help appreciated

 

[Lutfij]

You look at airflow fans if you're trying to cool your case innards. Airflow fans tend to have high CFM ratings.

You look at fans with high static pressure if the fans are meant to push air through a tightly packed fascia, like a heatsink or a radiator. mm H²O denotes static pressure. Since you want to look for a fan that is meant to exhaust air, anything is fine to get but an airflow fans is what you look for.

You should also look into getting the same fan on the rear as the one's on the front of your case(which are set to intake). Just an FYI, NZXT have horrible fans much like Corsair's fans.

 

[Dunkz]

ok thanks for that, makes sense i think the H7 Flow 2024 version has F120Q case fans, so your saying put a 120mm fan in the rear instead of the 140mm one i was looking at? i dont understand why you say get the same fan for the rear as the front intakes considering its 1 fan in the rear versus 3 in the front?

 

[Paperdoc]

It helps to know exactly what those specs mean, and that goes back to how fan performance is affected by surroundings.

To measure these things one has to set up a system to run the fan at full speed all the time through a wind tunnel that is fitted with a way to restrict air flow. Then you can measure actual air flow rate (typically in cubic feet per minute or CFM) at various levels of restriction. The measurement of the restriction is really the difference in air pressure (typically in mm of water column height) between the inlet and outlet sides of the running fan. Then you can draw a graph of air flow on the Y axis versus pressure difference (also called Backpressure) on the X axis. Roughly such a graph looks like a straight line (almost) from max airflow at zero backpressure down to essentially zero airflow at some higher pressure. At that pressure and anything higher, there is virtually NO air flow generated by the fan.

The specs they publish normally are only the "graph points" at those two limiting conditions - they don't usually tell you the details in between. So you get the MAX "Air Flow" spec with NO airflow resistance and the MIN "Pressure" spec that will cause NO airflow. With those you could sketch out your own graph.

A fan can be designed to yield max airflow with no real resistance but typically it will stop producing airflow at a moderate resistance or backpressure. Instead you can design to deliver much better airflow at significant resistance, but at the very lowest resistance its flow will be less that the other design. Most of this is in the blade design, but some also is in the surrounding frame details. If you take those two designs and plot on the same graph their respective "straight lines", the "Air Flow" fan will start at higher max airflow, but drop down to zero air flow at a lower backpressure than the "Pressure Fan". The Pressure Fan starts out at lower airflow on the left, but keeps pushing air better than the Airflow Fan at higher backpressure. The two lines cross each other somewhere in the middle.

In a computer, air flow thought the case experiences little resistance to flow. Even the foam dust filters (as long as they are not clogged!) on the intake side of intake fans provide little resistance, so the fans used for these positions are the Airflow Fans optimized for high flow with little resistance. On the other hand, trying to blow air though closely-spaced fins of a heatsink or radiator offers much more resistance, so one uses "Pressure Fans" for this. Numerically, an Airflow Fan is well suited to use where the backpressure is under 1.5 mm water, and any pressure requirement over that needs a Pressure Fan. Normally you do not get those "needs" specified in a case or rad or whatever. But you DO get those specs for the FAN to help you choose. They DO vary from one fan to another, so compare both specs for different fans.

 

[Dunkz]

Wow thanks for that response, i even drew a little graph for myself. but yeah shame there is no info specified for the case but at least fans are cheap and probably i assume the airflow fan will be sufficient

 

[Paperdoc]

That case is supplied with three front 120mm fans and one rear 120. That is not really a sufficient set of fans and does NOT provide good balance, so more fans are added usually. NUMBER of fans does not tell the whole story. What matters is the added AIRFLOW max values. This is especially important if you start to replace those three front 120's with 140 mm fans that can blow even more airflow.

There is debate about this next point, so this is my preference. Ideally you want the airflow capacity of all your intake fans to exceed the capacity of the exhaust fans. In fact, of course, what goes in MUST come out, so intake flow WILL equal exhaust flow. But a difference in capacity will show up as a difference in air PRESSURE inside the case versus outside in the room. This is important for small cracks in the case where air leaks through. If there is excess intake capacity the interior pressure will be higher than the room (by a VERY small amount!) and air will leak OUT of the case at cracks. If intake capacity is too low, air will leak IN at cracks, and it will carry room DUST into your case. So arranging to have more intake capacity WITH good dust filters on those fans will reduce dust build-up inside your case. The difference does not need to be large.

For a rough first "stab" at this you can just add up the max Airflow ratings of all your Intake fans and of all your exhaust fans and compare. Do NOT base this solely on fan COUNT. Next, consider that the real airflow capacity of your intake fans IS reduced slightly by the dust filters that ought to be mounted in front of them. This all gives you an ESTIMATE of whether intake capacity will exceed exhaust, thus producing inside your case a "positive air pressure". You can NOT be absolutely sure about that until the entire system is built and operating. There are ways to TEST all this and "tweak" fan settings if you want to, but many do not bother.

In that case the most likely position for adding exhaust fans is in the top. This might be just fans, OR you might mount up there a rad for an AIO cooler system for your CPU that blows air out of the top. Doing this "air balance" estimation with a rad in the top is trickier because the rad fans offer significant airflow restriction for those rad fans.

NOTE this with respect to fans at the top. At the top front there is a corner where you could mount one intake fan on the FRONT plus one exhaust fan on the TOP. Most of the time such an arrangement causes an airflow "short circuit" so that air from the intake gets "stolen" and blown right out the top, never contributing to overall case cooling. So, if you are doing just fans this way, do NOT mount an exhaust fan in the TOP right at the front. OR, if you are mounting an AIO system RAD in the top that extends all the way to the front, do not mount an INTAKE fan on the FRONT panel at the topmost location.

 

[Dunkz]

ok what an insane topic this is. i have a 360 AIO on the top (Fractal Lumen s36 v2), i assume those are pressure fans since they exhaust through the rad. then i have to consider the fan curves i have set since most of the time all of my fans are running in quiet mode at around 35% of their max RPM, cos my CPU never gets very hot.

It could be that if i add an airflow rear exhaust fan i could very well end up with airflow in < airflow out . . which i read is not desirable? I suppose it begs the question should i set my front intake fans to read off the CPU temperature so that when the AIO fans spin up in response to a rise in CPU temp, so do the intake fans?

i'm hoping someone out there has done the math already!

 

[JayGau]

Just an FYI, NZXT have horrible fans much like Corsair's fans.

What the hell are you talking? Corsair have some of the best fans on the market. I tried many over the years and ended up with only Corsair fans in my case because they are the ones giving me the best results (but you have to be willing to pay for their high-end models). The ML120 are among the best rated airflow/static pressure and the QL140 pushes way more air out of my case than any other 140 mm fans I have in other machines it's really impressive.

And just for fun of it, I googled best PC fans 2025 and the new Corsair QX120 are always in the lists.

 

[Paperdoc]

Actually, with those details I'd advise a different route. Look at the current intake / exhaust capacity balance. Front intake has 3 x F120Q, max airflow of 75 CFM each but reduced a little by dust filters. Total intake capacity a bit over 200 CFM. Rear exhaust is the same F120Q, airflow 75 CFM no filters. Top has an AIO with 3 x Aspect 120 PWM fans rated max 56 CFM each but significantly reduced by the rad fins, so maybe 100 - 125 CFM exhaust capacity. Total max exhaust is maybe 175 - 200 CFM. That is pretty close to balance already! However, we do not know if it is really "ideal" under all conditions.

Next I advise you change the way you have your fan PROFILE settings - that is the item for each fan header that is the "strategy" for how it decides what is the right fan speed for a given temperature measurement. (Fan header MODE is the setting for what signal type (Voltage or PWM Control) it sends out to achieve that decided speed.) Setting to Quiet means that your fans always will run SLOWER than what the makers consider "ideal". But more importantly that setting REALLY limits the max fan speed when your system is working hard and getting hot, so it get too LITTLE cooling in those conditions. Remember, with fans "there is no free lunch". Proper cooling means you DO get modest noise. You get more when you work hard. If you force slow fans for quiet, you ALSO force higher temperatures for your whole system.

Set your CPU_FAN and CHA_FAN headers to use the default "Standard" or "Normal". When your system needs only modest or little cooling the fans WILL run slow and quiet, but they WILL speed up when they need to.

As to changing your fan types, you may want to leave them as they are (1st paragraph). Changing the rear one to 140mm size will increase the exhaust capacity and overall air flow a bit, and probably result in negative pressure inside your case. The other path would be to take into account my comment on airflow "short circuit" in the case top front. You might want to remove the top 120 mm intake fan on the front to avoid that flow pattern, but that would reduce intake by about 75 CFM. We can't know how much, but SOME of that airflow really is NOT doing its job anyway. But then if you replace the remaining two front intake fans with 140mm ones (the F140Q's are rated for max 103 CFM each) that raises the intake total back to nearly 200 CFM (after a small allowance for dust filters) and we're close to balance again.

Regarding which headers for what, the CPU cooling units (the AIO rad fans) definitely should be connected to the CPU_FAN header because it regulates its fan speed according to a temp sensor inside the CPU chip. ALL of your case vent fans shuld be connected to CHA_FAN or SYS_FAN headers that use a different temp sensor on the mobo.

 

[Dunkz]

thanks so much for the analysis. i will meditate upon it! fyi the case did not come with a rear fan already installed, just the three front fans. so from your para 1 probably i am in an intake surplus at the moment, so the question to meditate upon is whether i install a 120mm fan in the rear to achieve potential balance, or just leave it without the rear fan.

My fan curves do ramp up in response to CPU temp, they start off around 35% (hence Quiet) until CPU temp hits about 50 C and then they start to increase up to 100% RPM when CPU temp hits 70+ C, something like that. so i think that's ok

 

[Phaaze88]

i have a 360 AIO on the top (Fractal Lumen s36 v2)

Lumen S36 V2

Customize your CPU water-cooling from subtle to stunning with Lumen’s six addressable LEDs that you can command via motherboard or controller. Compatible with most common Intel/AMD sockets and RGB certified by industry standards, the Lumen offers high-end cooling performance and premium ARGB...

www.fractal-design.com

Pump-in-radiator design(that black box). The pump won't last as long if you leave the radiator up there.