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Relative merits of Inlet or outlet mounting of fans

EBM/Pabst has some good technical info on fans inlcuding specs on all
the fans they make. 


You can order EBM/Pabst fans from 

 and from


Typical of the kind of info available is the following regarding
whether it's better to have a fan blowing in (mounted at inlet)
or sucking out (mounted at outlet):

Advantages of placing the air mover on the inlet side:
 Positive pressure is maintained which prohibits dust and dirt from
entering through unsealed cracks and openings [assuming your fan main
intake has a filter you'll have dust anyhow].
 Increased turbulence within the system improves overall heat transfer
within thesystem and through exhaust outlets.
 The life of the air mover is extended because of lower operating
temperatures [the fan gets all the coolest air first].
 Ball bearings are preferred because they last longer and:
 are maintenance-free [when designed to remain lubircated for the life
expectancy of the fan]
 mount in any position
 align better and have longer life expectancy than smaller sized
 have better temperature and life ratings than sleeve bearings
 have lower breakaway torque (110 to 125%) than sleeve bearings (130
to 150%).
 Fan/blower life is extended when they are operated at lower

Advantages of placing the air mover on the exhaust side:
 Better control of air flow through location of inlet openings near
heat sources.
 Reduced noise levels because the exhaust is usually located away from
user's hearing.
 Heat generating devices, if located near the air mover, will be
placed away from the user, away from non-heat producing passive
components and close to the exhaust opening which will eliminate the
effect of heat on the rest of the system. [this point isn't especially
relevant for most aquarium hood situations]

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