Roof top ventilation fans - why not recommended for outdoor use

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Hey all

Simple question

I see roof top ventilation fans offered by lots of vendors (Rittal, Cosmotec) but in all cases I have seen they are not recommended for outdoor use, inspite of having suitable IP ratings.

Does anyone know why that is?

Is it due to it being generally bad practice to provide penetrations in the rood of an outdoor panel? Or some other reason?

Thanks

 

[waross]

I suspect that those are smaller units intended for roof mounted enclosure cooling, not building cooling.
An outdoor unit must be suitable for condensation when it is not running in cooler weather, it should be bird and rodent proof, and it should withstand heavy rain and possibly snow.
Bill
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"Why not the best?"
Jimmy Carter

 

[jraef]

It's the last issue for the most part, driving rain. You need considerable baffling in the air channel to avoid having windblown rain or snow get in when the fans are off, i.e. when it is already cold and the fans aren't necessary. In those pagoda style fan assemblies, there is too easy of a path for water to enter, and then it is entering in the worst possible place, the top, where gravity and Murphy's Law will ensure that it gets to the most critical parts inside.


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