How do I calculate how much airflow I need?
Several pieces of information are needed:
The amount of heat to dissipate or “get rid of”, in watts;
The allowable temperature rise in Celsius or Fahrenheit; and
The derived factor of 1.76 for Celsius and 3.16 for Fahrenheit.
With that, the formulas are:
Airflow(CFM) =1.76 X Watts divided by allowable temperature rise in Celsius (Delta T).
Airflow(CFM) =3.16 X Watts divided by allowable temperature rise in Fahrenheit (Delta T.)
This is a general rule of thumb for calculating airflow needed. Other factors that also need to be considered are altitude, hot spots, and humidity.

What is the relationship between RPM and airflow?
RPM and airflow are directly proportional. In other words, increasing RPM by 20% also increases airflow by 20%.

What can we do to lower the noise level in a fan?
1) Lower the RPM or the fan operating speed (this also lowers airflow.)

2) Check for obstacles in front of and behind the fan. If they exist, move the fan farther away. In general, obstacles on the intake side of the fan negatively impact the noise level more than on the exhaust side.

How do I determine my system's static pressure?
This is difficult to do without an airflow chamber. Typical system impedance for electronics equipment ranges between .05" and .15" of water.

范例 (網友補充, 是否正確,請自己判定):
　　例一：有一電腦消耗功率150瓦，風扇消耗5瓦，當夏季氣溫最噶30℃，設CPU 允許工作60℃，所需風扇風量計算如下：   
　　P=150W+5W=155W；△Tc=60-30=30  
　　Q=0.05×155/30=0.258CMM=9.12CFM(為工作所需風量)  
　　所以,應選擇實際風量為Qa之風扇  
　　  
　　  例二：有一SWITCHING電源供應器消耗功率250瓦，風扇消耗20瓦，當地夏季氣溫最高55℃，設該供應器允許工作95℃，所需風扇風量計算如下：   
　　P=250W+20W=270W；△Tf=95-55=40  
　　Q=0.09×270/40=0.6075CMM=21.44CFM(為工作所需風量)  
　　所以,應選擇實際風量為Qa之風扇
 

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