January/February 2018 • www.cemag.us 5
For example, for a small room that measures 10’ x
15’ x 8’ needing 50 ACH (ISO 7), you will need 1,000
CFM. Note how the ceiling height is included in the
calculation ( 8’). People often forget that the height of
the room directly impacts the CFM (air flow).
The calculation must be repeated for every classified room.
2. 3) HEPA filters
The cleaner the room (ISO 5 vs ISO 8), the
higher the required number of HEPA filters.
Generally speaking, a HEPA filter can supply
400 to 700 CFM. Every filter is different so make
sure to check the performance of the HEPA filters you use in your design. For our calculation,
we will use the average figure of 500 CFM.
For example, for a small room that measures
10’ x 15’ x 8’ needing 50 ACH (ISO 7), you will
need 1,000 CFM, therefore 2 HEPA filters.
The HEPA filters of this ISO
6 cleanroom are illustrated
by the blue circles.
Design of a Cleanroom
2. 2) Air flow (CFM)
Once you know the ACH that you need and the size
of each classified room in your cleanroom, you will
be able to compute the approximate required air flow
(CFM: cubic feet per minute), as illustrated below.
Required number of CFM (air flow)
Room volume in
cubic feet (ft3)
Length (ft) x
Width (ft) x
4 000 sq.ft x 8 ft =
32 000 ft3
÷ 60 minutes = 13 333 CFM
150 sq.ft x 8 ft = 1
÷ 60 minutes = 1 000 CFM