The air balance technician should have these **Square Areas in feet **formulas memorized.

square/rectangle = h x w

Circle = pi r^{ 2}

Oval =r_{1} r_{2}

Now you can take any one of these formulas and divide it by 144 to get the **cubic feet**.

When air balancing **Pulley Speeds** are very important. If you don’t have a tachometer of some kind to take the actual measurement, you can calculate the speeed in the following way:** **

Speed of the motor pulley x diameter of the motor pulley divided by the diameter of the fan pulley;

Motor Speed= 1750

Motor Pulley = 2.75″

Fan Pulley = 7″

1750 x 2.75 = 4812.5

4812.5 / 7 = 687.5

If you need to increase the speed of the fan just calculate the percentage of increase and either increase the motor pulley size of decrease the fan pulley size