# Cooling efficiency - Noctua 200 on two 240 Radiators

#### hannibalxali

##### New Member
I want to add a noctua 200 to two 240 full copper radiators using custom mountings. Springs from each corner of the fan to the outer corners of the Radiators with suitable screws to fix it in place. My only concern is about the difference between a one 200 mm fan and four 120 mm fans regarding efficiency. Knowing that:

200mm has a 150 CFM, direct contact area is π x r² » π x 10 = 314 Sq cm

120mm has a 107 CFM, direct contact area of four fans is 4 x π x r² = 452 Sq cm

I just multiplied the CFM by the area affected to determine the difference between both methods:

200mm ». 150 CFM x 314 Sq cm = 47100

4 x120mm »107 CFM x 452 Sq cm = 48364

I don't know what are the final numbers but i think that they determine the difference between two methods.. Are my calculations correct? If they were correct then there will be no difference regarding cooling performance. But way less noise with the big fan and probably a better performance in real life, plus the easier control with just one cable and less power consumption of course. Thank you for reading and answering Please see the image provided

#### maxfly

##### Member
I would be concerned with the 200s static pressure vs the 120s. Most 200s don't push thru grills and rads very well.

#### Zerileous

##### Senior Member
You'd probably at least need to do push/pull, but I agree with maxfly. Static pressure is often a factor of RPM, which the 200ml fans tend avoid. The A20 pictured has a max static pressure of 1.08 mm H₂O at 800rpm. Generally anything under 2 is not well suited for a radiator. Of course a curve is better data if it can be found, since comparing one fan at 800rpm to another fan at 2000rpm doesn't tell the whole story. But the max for the A14 at 2000rpm is 4.18 mmH2O.

#### bassnut

On top of static pressure you are also giving up unused surface area ….. From the looks of your pic I see about 10% - 15% of usable rad fins you are not taking advantage of, there will be no air flowing through those fins.

Find some 120 fans you can live with the sound they generate and use software or a fan controller to turn them down when they are not needed to run full out.

#### TeslaHUN

##### New Member
U can definately do it . Dont worry about static pressure . Here is my Video when i tested 20cm weak CM rgb fans on a 45mm thick radiator :
Noctua NF A20 is much more stronger then these slim CoolerMaster fans .
Many people (including myself ) are using 20cm Noctua Fans on their Mo-Ra 420 radiators , and they are doing just fine.
For 2x 240 radiator , i would make some kind of shroud and put the big fan on middle , and in that way the fan would blow air on almost all of the radiator's surface area.
Someting like this : https://www.brotherstrucks.com/images/fs06066.jpg

#### Zerileous

##### Senior Member
I suppose it really depends on what you are cooling. A single CPU with a single digit core count, sure, multiple components or HEDT, maybe not.

#### ehume

##### Member
And remember that the swept area of a fan is circular -- about 76% of the side-squared area.

#### Zerileous

##### Senior Member
Aquatuning has a US store as well \$47.05.

Cool thing I forgot about that. Do you feel like it needs or benefits from push / pull? How does it compare to a conventional 240mm rad?

#### Woomack

Push and pull were giving me similar results but I switched to push with the exhaust in front of the case (there was space for 200mm rad) because it was giving me better results once the case was closed.
240 rad is pretty much weak for modern setups. It's like 240 for CPU only and 240 for GPU only ... assuming that both are rather an average wattage and not 250W+. 2x240 is easier to install in most modern PC cases than the single 200x200. In the end, results should be similar but there are too many variables to say straight (airflow, air pressure, fan speed etc.).

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