Test Block in AMCA Standard

"In addition to the fundamental volume specifications, combustion

process fans, particularly larger fans, are often specified for

two conditions . . . actual and test block. The actual condition

is the calculated volume (including excess air) and pressure

requirements. The test block condition is a theoretical duty

that includes some safety factor beyond the actual volume and

pressure requirements. The fan selection for the application

should be capable of meeting both conditions with good efficiency,

economy, and stability. Whenever possible, the actual condition

should represent the most efficient point of operation for the

fan selected for the application. "

http://www.mpair.com/library.active/nyb.engineering.letters/engltr10.pdf