120mm vs 140mm

[jetnoodles]

Hi. My case can either fit 3x140mm fans or 4x120mm fans. Which one will give me better airflow?

[RONOTHAN##]

They're both gonna be within margin of error of each other, but the 4x120mm configuration will be marginally better

[Chris Pratt]

Is that in total or all for a front intake or something?

[Michael2]

no idea if this is the correct way of calculating this but oh well: 3x140mm = 420mm, 4x120mm = 480mm so you are getting more fan mm with 120mm fans. Also I believe 140mm fans can spin slower to achieve the same amount of airflow so they are quieter.  

[jetnoodles]

9 minutes ago, Chris Pratt said:

Is that in total or all for a front intake or something?

there will be two of these for intake

(front and side)

[Chris Pratt]

11 minutes ago, NOV654 said:

there will be two of these for intake

(front and side)

And that's why I asked. Don't just fill the slots because they're there. Your airflow should be a smooth line from intake to exhaust that washes over your components in between. You absolutely do not want different directionalities to the airflow, like both front and side intake. This will create eddies in the airflow that actually prevent air from reaching your components.

[cmndr]

11 minutes ago, Michael2 said:

no idea if this is the correct way of calculating this but oh well: 3x140mm = 420mm, 4x120mm = 480mm so you are getting more fan mm with 120mm fans. Also I believe 140mm fans can spin slower to achieve the same amount of airflow so they are quieter.  

Close. If you want a very rough calculation it'll be surface area of the fan.

So 4 x120 x120 = 57,600 mm^2 vs 3*140*140 = 58,800 mm^2

 

So as a baseline these two will be VERY VERY close. Within around 2%.

Now, there are ways to improve this calculation.
1. Use area of a circle that's ROUGHLY the size of the fan blades (4x[120-4]^2 / 4) vs (3x[140-4]^2 / 4) though this gets you a very similar result when comparing ratios. (the -4 comes from ~2mm of overhead on each side of a fan blade for the casing and some tolerance
2. If you know anything about a given case you could in THEORY do airflow simulations. THIS gets really complex.

----

High level - it probably won't matter a ton which you go for. My general recommendation would be for the 140mm fans. These could work with future 140mm based radiators and generally you'd expect the sound pitch to be at a lower frequency with the larger fans. Most people prefer lower pitched noise.

[Michael2]

9 minutes ago, cmndr said:

Close. If you want a very rough calculation it'll be surface area of the fan.

So 4 x120 x120 = 57,600 mm^2 vs 3*140*140 = 58,800 mm^2

 

So as a baseline these two will be VERY VERY close. Within around 2%.

Now, there are ways to improve this calculation.
1. Use area of a circle that's ROUGHLY the size of the fan blades (4x[120-4]^2 / 4) vs (3x[140-4]^2 / 4) though this gets you a very similar result when comparing ratios. (the -4 comes from ~2mm of overhead on each side of a fan blade for the casing and some tolerance
2. If you know anything about a given case you could in THEORY do airflow simulations. THIS gets really complex.

----

High level - it probably won't matter a ton which you go for. My general recommendation would be for the 140mm fans. These could work with future 140mm based radiators and generally you'd expect the sound pitch to be at a lower frequency with the larger fans. Most people prefer lower pitched noise.

im not even going to try to understand any of that

[cmndr]

3 hours ago, Michael2 said:

im not even going to try to understand any of that

The first bit is that you need to SQUARE the fan size since the fans are 120x120 and 140x140.

The other stuff is basically overkill.

[Michael2]

3 minutes ago, cmndr said:

The first bit is that you need to SQUARE the fan size since the fans are 120x120 and 140x140.

The other stuff is basically overkill.

right ok

[thrasher_565]

but that's also with no obstructions in front or behind the fan. so 120mm fan will do better as they can handle sp better. not only that just because a fan is louder dose not mane its louder to you. 

[WoodenMarker]

It depends on the fans, where they're mounted, and the case. 

[Dogzilla07]

Rule of thumb is always like this (assuming you're not cash strapped), and assuming it's at least january 2024 (going through the list sooner, means no LCP 140mm options):

 

1. Fans have to be made from (Liquid-Crystal Polymer) and use a good motor

 

2. Always prioritize >30mm fan depth (regardless of fan size, but check reviews first).

 

3. quality 140mm fans will always be more silent unless they're <30mm in depth (the reason @thrasher_565mentioned better SP@120mm is inferior fatness)

 

4. quality 180mm will usually be more silent unless they're <38mm in depth

 

4. Case has to have meshfilter in the front (Phanteks/Lian Li quality/size of holes at least)

 

5. Fan mounting brackets need to be non-obstructive for a given fan size so there's not weird noise, ideally interchangeable brackets.

 

6. Case has to have adequate exhaust venting design (holes in the back at about Fractal Design Torrent size), or exhaust fan

 

7. Case in general has to have a good airflow design inside like @WoodenMarkermentioned.

 

8. ???

 

9. profit

[NorKris]

7 minutes ago, Dogzilla07 said:

Rule of thumb is always like this (assuming you're not cash strapped), and assuming it's at least january 2024 (going through the list sooner, means no LCP 140mm options):

 

1. Fans have to be made from (Liquid-Crystal Polymer) and use a good motor

 

2. Always prioritize >30mm fan depth (regardless of fan size, but check reviews first).

 

 

just wanted to say that thiicc isnt always better   the 28mm arctic(120argb) is not as good as the 25mm arctic  (12argb)

[Dogzilla07]

@NorKrisYeah definitely, it needs to be properly scaled up and a design optimized for that depth increase xD, but I just mean in the sense, that it's not ideal to have 140x25mm, and 180x25mm designs, as you're getting further and further away from the golden ratio (And 120x25mm isn't exactly peak golden ratio either xD)

 

The Arctic P120 ARGB have the same problem Lian Li UNI SL120 had, ~92mm impeller size, due to space restrictions from the innovative ARGB fan connecting mechanism. which in turn put those fans even further from the golden ratio. That's why Lian Li released AL120 UNI fans, which now have impeller size closer to regular 120mm impeller size.

 

When @thrasher_565says 120mm can handle SP better, he doesn't mean that 120mm inherently do static pressure better, just that they have an advantage compared to >120mm cause at 25mm they're closer to the golden ratio. And because the designs for most 120mm fans from most companies spend more time getting tweaked in the simulations.

[thrasher_565]

bot only that the bigger the fan the bigger the moter need to drive the fan blades. more surface area more resistance so they have to turn slower. but because the moter is bigger can mean more nose...

 

i dont no i just heard smaller the fan the bitter the static presher is maybe because it can turn faster we just recently got the t30 still hard to get and cost alot thow...and gn has a fan tester so we just need to hold off a bit logger...then we will crak the nut wide open

 

as for 180nn fans well there only 2 on the market...so... in terms of thow 2 vs the 200mm fans the seem to about the same and because the ss fan can go faster then 800rpm it beats the 200mm fan but there loud that that speed.

 

lintel we see the t30 be made in to a 140mm fan still think 120mm is better but thats imo unless you have a wide open case with no grill then the 140 sould be better in that case.

Edited February 11, 2022 by thrasher_565