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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
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
• 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
• Reduced noise levels because the exhaust is usually located away from
• 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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