Note: These are rules of thumb and general calculations for informational purpose only.

Bathroom Exhaust Fans:

The Uniform Building Code recommends that a bathroom exhaust fan be able to deliver 10 air changes per hour. Therefore, to calculate the cfm rating of the fan you should select, follow the following steps:

Step 1: Calculate the cubic feet of your bathroom (length x width x height)
Step 2: Divide by 60 (the number of minutes in an hour)
Step 3: Multiply the result by 10 (the number of recommended air changes per hour)

The result represents the recommended cfm rating for your bathroom fan.

Note:  Make up air is required for the bathrooms whenever there is exhaust in the bathrooms.  A good rule of thumb is to compare the above with 2 CFM/SF.

Equipment Heat Load CFM:

Most electronic equipment will generate heat from the power supply.  Assuming that 30% of this heat is not used then it is disipated into the room raising the temperature slightly.  To calculate the amount of  CFM required to remove this heat, follow these steps:

Note: 1 W = 3.412 BTU/hr.  Equation: BTUH=CFM x 1.1 x 1.085 (delta T)

For example,

Step 1: Calculate the heat load generated by the rejected heat from the equipment in MBTU/hr
Step 2: Divide by 1.085
Step 3: Divide by the temperature difference between the room and the coil.  Typically (74 F - 55 F)