Understanding fan specs

I have confirmed that the specifications published for AIO cooler fan are per fan, not per unit.

Over the last 12-18 months fan specifications have plummeted across most, if not all AIO cooler manufacturers. So I'm wondering how coolers can be as efficient or effective with such appalling specifications.

Example. The H115i fans are 104cfm, 3.99 mmH20. The H115i Pro fans are 47cfm and 1.27 mmH20.

One would assume the radiator and pump work the same way, so cooling performance is down to the fan. Pump speeds seem to be typically the same or close to, across different brands.

Correct me if I'm wrong, but when calculating airflow and static pressure you add the airflow, but the static pressure remains the same, regardless of how many fans are attached.

So, for the H115i the total airflow across the 280mm surface is 208cfm, and the static pressure across that surface is 3.99 mmH20.

For the H115i Pro the total airflow is 94cfm and 1.78 mmH20 static pressure.

How can the H115i pro be as efficient at the H115i given these figures?

Can someone please explain it to me. thanks

Over the last 12-18 months fan specifications have plummeted across most, if not all AIO cooler manufacturers. So I'm wondering how coolers can be as efficient or effective with such appalling specifications.

The deep push into RGB fans complicates the power requirements of many fans and forces a reduction in speeds to keep the total power/current down.

You don't see a lot of 3000 rpm LED fans. However, this stuff is trendy to be sure and perhaps it is just the pendulum swinging back the other directions from 2700 rpm ear splitters. Either way, the fans are not the critical piece and you can use what you want in most applications with no penalty. See below.

You have to equalize to RPM when comparing fans. Technically, P-Q curves are not linear, but this all you can do since those are almost never provided. It is close enough most of the time. (Fan 1 moves 80 cfm at 2000 rpm; Fan 2 move 50 cfm at 1000 rpm -> Fan 2 is better since fan 1 would only move 40 cfm at 1000 rpm). This assumes you are not willing to run the fans at the highest speed possible all the time. Most people are not willing and that makes performance in the middle ground more appealing.

One would assume the radiator and pump work the same way, so cooling performance is down to the fan. Pump speeds seem to be typically the same or close to, across different brands.

Strangely, most of them are made by the same OEM, so yes, lots of similarities. However, pump speed is rarely a meaningful setting on most AIO coolers with short hose runs and relatively low restrictions. Only those running high core count CPUs and long professional workloads are likely to see much difference between 2000 and 3000 rpm. 7900X? Maybe. Experiment and see, but it would be stunning to see more than 1-2C.

The radiator is where you can see a lot of variation or innovation in custom loops, but in AIO they will all be very similar. Back to fans, with coolant deltas in the single digits at worst, the possible reduction in temperature is going to be small even with high speeds. Cutting your coolant delta from +6 to +4C would be a big gain. Still only -2C on the CPU. Not as exciting. Pick your fans for sound and aesthetics.

Correct me if I'm wrong, but when calculating airflow and static pressure you add the airflow, but the static pressure remains the same, regardless of how many fans are attached.

No, other way around. Static pressure is cumulative and airflow is not. 2x120mm 50 cfm fans working together still only move 50 cfm -- in free air. The pressure does stack and this can be helpful at low speeds. However, as fan speed increases, the usefulness of pressure diminishes and the difference between push and push-pull start to shrink.

The other thing to note is static pressure is the amount of negative pressure required to bring a fan from XXX RPM to 0. This makes it extremely RPM dependent. A little 40x40mm fan with a 5000 rpm max will have a flattering static pressure value (at 5000 rpm). It still only moves 9 cfm at that speed, so not something you want on the radiator. Airflow is still what matters. Not static pressure. What makes it complex is the level of resistance provided by the radiator. A 50 cfm fan cannot put 50 cfm through a radiator. It is likely to only move 25-30 cfm. That is at max speed. The 50 cfm fan at 400 rpm likely moves a trickle of air through the radiator. At lower speeds, the combined pressure has a more beneficial effect.

The specifications on the PRO model are lower because the fan speed is nearly half that of the prior model. That means it does in fact only move half the air at 1000 rpm versus the 2000 rpm of the prior fans. However, the prior 100 pages of this forum is filled with people who hated the SP140L and its sound at 1000 rpm, let alone 2K. There was a definite period of cooler wars where companies kept strapping on really loud and really fast fans to win that product shootout by 0.8C. Reviews never bother to (or at least rarely) run tests at the same speed. Corsair finally did the smart thing and put quiet fans on the cooler. For the <1% of people who who are running extreme set-ups on $1000 processors, they can buy the 2000-3000 rpm fan if they think they need it. The other 99% do not. Even my 8700K at 5.0 Ghz is pretty trivial in the coolant delta rankings. +5C in 100% CPU load conditions, at 900 rpm with pretty RGB fans. I could run 2000 rpm fans and take another 2C off, but why bother? That's a bad trade for noise. People who think they are taking 10C off their CPU temps by changing fans had a different problem to begin with. There just isn't a lot of gain to made in terms of fans speed. Well, this was longer and more detailed the first time, but the usual Forum bug bit me and washed the page out on submission. This will have to do.

Thanks for that explanation. As usual, very informative.

When I first bought my H115i I had the stock fans. I think I recall the noise annoying me as I spent a lot of time hammering the system. But I was running a I7-6900K at the time. Then I upgraded to the I9-7900X and the FUD got the better of me re bad thermal performance reviews. So I upgraded to the Noctua NF-F14 iPPC 3000 RPM PWM fans. Static pressure of 10 and Airflow of some ridiculous amount. But the noise on those was worse at high speeds than the SP140L's

So I swapped to the NF-F14 iPPC 2000 RPM PWM; one for the noise and also because they have a lower minimum speed (350 vs 760)

I don't know if I had some other problem (I believe we discussed this about a year ago), but I managed to drop my temps from 80c to 70c under load (Eg x264). But I think there might be other contributing factors. My case is much larger and has 11 other fans now.

Anyway, I have to replace my H115i because off rattling. I think I might go for the H150i Pro and use the NF-F12 2000 RPM iPPC PWM fans.

I've not been able to push my temps over 73c in my current build. It will be interesting to see how well the H150i performs with the same fans I am using on the H115i.

I don't care about RGB or aesthetics.

thanks for your help.

So with your CPU and if you run applications with x264 or similar instructions, fan speed may matter on the longer batch jobs. On my Haswell-E (215W), I found 1250-1350 RPM to be the sweet spot for noise vs performance with little gain beyond that on a 280mm with 140x2. Yup, the 3000 RPM version of the A14i is one of the few fans I sold on almost immediately. There is little to be gained between 2000 and 3000 rpm and the large increase in current on the 3000 rpm model makes it hard to use with many fan headers. The 2000 rpm version however was a mainstay for a long time, until finally being replaced by the ML140 PRO in black. I still use both, depending on the case and system.

So 280mm vs 360mm. At maximal speeds, it's probably going to be a wash. The 360mm has a slight advantage at low speeds. Certainly the 360mm with 2000+ rpm NF-F12 or black ML120 PRO fans would be sufficient cooling with more headroom than needed. That's a bit of a toss up for noise levels for 3x120@1500 vs 2x140@1200. I would probably decide based on how the radiators fit and what other size fans are in your system. I finally managed to put together an all 140mm fan dual cooling system and I am loving the load noise. I have a strong preference for 140 over 120. Not everyone else does. If you already have a mix of 120 and 140 fans, it likely makes no difference and I would decide based on fit. If that 360 can go top or front intake on your case, I would say sold. One of the reasons I specifically stuck with 280mm x 2 for my build is I can arrange them in 3 different locations. A 360mm would have only one placement. I like to keep options open.

If you don't crave the RGB, skip it. It's a lot of expense and management. Sometimes I wish I could turn back the clock and undo it, but I think I am addicted to the versatility.

One thing that the fan specs (and the fan manufacturers) don't tell you: when using fans on a radiator, you get diminishing returns as you crank the fan speeds up.

You can only cool the coolant so much - you're limited by the temperature of the air going through the radiator and the ability of the radiator to exchange heat - regardless of your fan speeds. Back when the ML-RGB came out, with the lower fan speeds (and specs) than the ML "Classic", I experimented with this - I intentionally limited the fan speed of my ML "Classic" fans on my (at the time) H100i V2 cooler to the max speed of the ML-RGB fans. Much to my surprise, there wasn't a big difference in performance between that (1600 RPM) and running the ML "Classic" at their full speed (2400 RPM) ... less than 1C difference. There was, however, a pretty significant difference in the noise level - though those MLs are definitely much, much, much quieter than the stock SP fans.

I would probably decide based on how the radiators fit and what other size fans are in your system.

Starting to get a little off topic, but...

My case is now a Thermaltake W100. Massive case. Top will fit a 600mm radiator with ease. (https://www.thermaltake.com/products-model_gallery.aspx?id=C_00002802).

It has the side left and right fan brackets. I too prefer 140mm but the case brackets suit 120mm fans better. So, two bottom, two left, two right, two top, one back, two front. Plus 2 on H115i. They are a mix of Noctua Redux 140mm 1200 RPM and 120mm 1200 RPM PWM fans. (https://noctua.at/en/nf-s12b-redux-1200/specification)

The 120mm iPPC fans are hard to get. I rang a few suppliers earlier and I can't get three. I already have the 140mm fans so I might have to go H115i. Would also save me $110 for the fans and $56 for the cooler.

I managed to find someone with the H115i.

If you don't crave the RGB, skip it. It's a lot of expense and management. Sometimes I wish I could turn back the clock and undo it, but I think I am addicted to the versatility.

My W100 does not have the Window side, it has the vented panel so that I could add the extra fan bracket. RGB doesn't improve cooling and if it doesn't add some performance benefit then I'm not interested.

The only time RGB is useful to me is when I want to sell a system. It's sad how many people will only by a system if it has flashing lights and lots of colors everywhere.

I too prefer 140mm but the case brackets suit 120mm fans better. So, two bottom, two left, two right, two top, one back, two front. Plus 2 on H115i.

That was my impression looking at the case in photos and why I thought the H150i might work well for you. I thought the PPC prices might have finally dropped universally, but I guess you are always stuck paying heavy import costs. If they are more readily available, ML120 and ML140 PRO black fans are a good substitute for the Noctua, although I do understand wanting to stick to one fan type.

That was my impression looking at the case in photos and why I thought the H150i might work well for you. I thought the PPC prices might have finally dropped universally, but I guess you are always stuck paying heavy import costs. If they are more readily available, ML120 and ML140 PRO black fans are a good substitute for the Noctua, although I do understand wanting to stick to one fan type.

I have no loyalty to any brand. I buy what fits in my budget, and what meets my (perhaps naive) performance expectations.

I would have gone with the H150i had I been able to get the fans I wanted. I didn't even think of the ML fans.

The ML Pro black's are $29 each, versus the Noctua's @ $45 each. A couple of things dissuaded me on the ML Pro's when I was building this W100 - The advertisement says they are case fans, and the noise was 37 dBA. https://www.pccasegear.com/products/36033/corsair-ml120-pro-120mm-premium-magnetic-levitation-fan-black

Anyway, I'm sure I'll have another chance in 6 - 9 months when this new pump starts rattling.

Prices here I do not believe are based on import costs. I did read some news articles on the subject of inflated Australian prices, but it really just comes down to price gouging and exploitation. Eg. Graphics card prices have plummeted now that the Crypto bubble has burst. Here the prices haven't budged a single cent. Anyway.. way off topic..

What "37 dBA" doesn't tell you is the sound of the fan itself ... just the total "sound pressure".

Most fans, when they get that fast, have a hum or high-pitched whir to them. Case in point ... the stock fans that ship with previous generation coolers. The ML fans have more of a "whoosh" and it doesn't sound like a jet - more like a strong wind.

Finally ... there's really no need to run these things at full speed. You won't get much performance improvement over 1600-1800 RPM. And at that speed they are really quiet.