What's CFM, and how is it important in case fans?

[LowVitality]

I was looking at the specs of my CF120 Plus case fans and found out it only has a CFM of 52.5. The MF120, which I presumed was worse due to it being slightly cheaper in most retailers, has a better CFM of 60.6 CFM. I only bought the CF120 Plus since they came from a brand that I trust and they look cool. Did I buy the more expensive but lesser product? Or am I getting ahead of myself? Are there any benefits for case fans with low CFM?

[SkilledRebuilds]

It's how much air they can move...
Combine it with the decibel metrics though... because up to 60-70CFM is great, but not if its a jet engine sound of extreme decibels.

[SignatureSigner]

CFM is the rate in which the fan can move a certain amount of air. CFM means Cubic Feet per Minute. CFM measures the volume of air in cubic feet for each minute it moves.

 

Just make sure it doesn't sound like a yet engine at a higher speed.

[JamesTheFolf]

2 minutes ago, LowVitality said:

I was looking at the specs of my CF120 Plus case fans and found out it only has a CFM of 52.5. The MF120, which I presumed was worse due to it being slightly cheaper in most retailers, has a better CFM of 60.6 CFM. I only bought the CF120 Plus since they came from a brand that I trust and they look cool. Did I buy the more expensive but lesser product? Or am I getting ahead of myself? Are there any benefits for case fans with low CFM?

CFM = Cubic Feet (of air) per Minute

[LowVitality]

9 minutes ago, SkilledRebuilds said:

It's how much air they can move...
Combine it with the decibel metrics though... because up to 60-70CFM is great, but not if its a jet engine sound of extreme decibels.

My case fans have an CFM of 52.5, yet there are cheaper case fans or fans with the same price that have the same CFM or even a higher CFM. Did I waste money on case fans with less performance?

[mariushm]

The CFM value will be proportional to the rpm value (how fast it spins) ...  a fan may have higher CFM but reaches that amount at higher rpm, meaning it's more noisy.

 

CF120 is:

 

FAN Speed	500~1800 RPM±10%
Fan Air Flow	52.5 CFM
Fan Air Pressure	2.08 mmAq
Fan Noise Level	≤28.8 dB(A)

 

MF120 is :

 

 

Fan Speed	500~1800 RPM±10%
Fan Airflow	60.6 CFM
Fan Air Pressure	1.73 mmAq
Fan Noise	≤35 dB(A)
Fan Speed (with LSP)	400~1450 RPM±10%
Fan Airflow (with LSP)	48.3 CFM
Fan Air Pressure (with LSP)	1.1 mmAq
Fan Noise (with LSP)	≤29.5 dB(A)

 

So the MF120 can push more air, but with much higher noise (35dB vs 28.8dB).. with the noise reduction (basically making it run at 9-10v or something like that), you get less CFM and still higher noise amount.

The MF120 is also less good at air pressure, meaning the amount of air flow will be affected more significantly by obstructions in the air path (if your case has mesh, or a grill  with lots of metal through which the fan needs to push air... it won't do well. 

 

[LowVitality]

3 minutes ago, mariushm said:

The CFM value will be proportional to the rpm value (how fast it spins) ...  a fan may have higher CFM but reaches that amount at higher rpm, meaning it's more noisy.

 

CF120 is:

 

FAN Speed	500~1800 RPM±10%
Fan Air Flow	52.5 CFM
Fan Air Pressure	2.08 mmAq
Fan Noise Level	≤28.8 dB(A)

 

MF120 is :

 

 

Fan Speed	500~1800 RPM±10%
Fan Airflow	60.6 CFM
Fan Air Pressure	1.73 mmAq
Fan Noise	≤35 dB(A)
Fan Speed (with LSP)	400~1450 RPM±10%
Fan Airflow (with LSP)	48.3 CFM
Fan Air Pressure (with LSP)	1.1 mmAq
Fan Noise (with LSP)	≤29.5 dB(A)

 

So the MF120 can push more air, but with much higher noise (35dB vs 28.8dB).. with the noise reduction (basically making it run at 9-10v or something like that), you get less CFM and still higher noise amount.

The MF120 is also less good at air pressure, meaning the amount of air flow will be affected more significantly by obstructions in the air path (if your case has mesh, or a grill  with lots of metal through which the fan needs to push air... it won't do well. 

 

So my case fans push less air but are more quieter in most cases I guess. Since I have a case with a mesh front, the higher air pressure would be more beneficial, right?

[mariushm]

Yes. There's static pressure optimized fans, those that are meant to be put on AIO radiators, those would be ideal for pushing air through obstructions. 

Then there's case fans, with high cfm , low air pressure, which basically are designed to be mounted on case, with just some grill so you won't shove your fingers in the blades, so minimal blockage 

 

Mesh ... it can be bad or it can be not so bad , it really depends on the proportion between plastic/metal and open holes ... 

 

This is ok for case fans : 

 

 

This is NOT ok for case fans ... too much air flow blocked, a case fan is unlikely to reach that CFM value with so much obstruction 

 

 

[LowVitality]

2 minutes ago, mariushm said:

Yes. There's static pressure optimized fans, those that are meant to be put on AIO radiators, those would be ideal for pushing air through obstructions. 

Then there's case fans, with high cfm , low air pressure, which basically are designed to be mounted on case, with just some grill so you won't shove your fingers in the blades, so minimal blockage 

 

Mesh ... it can be bad or it can be not so bad , it really depends on the proportion between plastic/metal and open holes ... 

 

This is ok for case fans : 

 

 

This is NOT ok for case fans ... too much air flow blocked, a case fan is unlikely to reach that CFM value with so much obstruction 

 

 

My case has been praised for its airflow, so I think there won't be any problems in that regard. Anyways, thanks for explaining. I learned a quite a bit.

[AntoniGibon]

OK, so everyone is providing the fan speeds like this example:

Fan Speed	500~1800 RPM±10%
Fan Airflow	60.6 CFM

 

But one super important parameter is never discussed, it is unlikely that fan airflow is 60.6 CFM constant across the whole range of 500~1800 RPM±10%.

 

So where the h.. are the charts showing the detaild values of CFM in relation to RPM?

If I have 3 of 120mm fans intake in front of my case and 3 of 140mm exhaust without this charts HOW can I keep a negative pressure and how can I set my fan controllers correctly to make them work properly as I really want? :D:D:D.

 

 CFM in nearly all the fan specs is given a MAX value but I don't want my computer case to be a JET taking off!?

 

There is so many topics and articles about case fans so excited  about n->nnn RPM and x (constant ???) CFM. Where is the X-XXX CFM charts!?

 

Can anybody help me? :D

[AntoniGibon]

I've opened the new topic instead, sorry admin!

[mariushm]

If you want graphs and all the crap, request them from the manufacturer, or buy fans that provide those datasheets.

 

Stores that sell electronic components (for example Digikey, Mouser, Farnell/Newark, RS Components, TME.eu) sell electronic components but also fans, heatsinks, thermal management solutions (pastes, pads etc)

The downside is that majority of fans are normally supplied without the 3-4 pin connector and it's up to you to install the connector.

 

For example, see 18134 fans here : https://www.digikey.com/en/products/filter/dc-brushless-fans-bldc/217

and if you filter to get only 12v fans, with 92...140mm size, and in stock, you get  426 models : https://www.digikey.com/short/m740rmnz

 

So for example let's take a common relatively cheap Sanyo Denki fan 92mm fan : https://www.digikey.com/en/products/detail/sanyo-denki-america-inc/9A0912S402/6192067

 

You can check the datasheet on that page or get the Sanyo Denki catalogue and find the part number : https://www.sanyodenki.com/archive/document/product/cooling/catalog_E_pdf/San_Ace_E.pdf (see page 147-149 in catalogue for model linked above)

 

9A0912S402 is 9A0912S401, without pulse sensor, so you can look in datasheet at 9A0912S401 (or pages 147-149 in catalogue) like I said... and see the graphs static pressure vs air flow at 3 or more voltages, usually 12v (nominal voltage), a low voltage, close to minimum the fan can handle (6v), and some over voltage (usually 13.2v, maximum allowed by atx standard as in 12v +/- 10% or 13.8v , the nominal lead acid battery voltage when charging)

 

 

And here's static pressure vs airflow