# Problem in hood designing



## saadat68 (Mar 15, 2017)

Hi
I make a hood with this design :
http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=40&t=19965

But I didn't know that I can't add any fittings over the hood (just can add a 45 degree fitting). I need add minimum five 45 degree fittings 
So I must change my design. If I add a second blower can I solve the problem ?

*Which design has more air speed in pipe number 1 ? 
If I have lower speed than first design (first image) hood doesn't work*


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## 4metals (Mar 15, 2017)

View attachment dual fan hood.pdf


This is a sketch of using the smaller fan to power the hood and a larger fan to increase the push to overcome length of run and fittings. The smaller blower should be about 4" and the hood exhaust 6" and the larger blower 8". The good part is they are all regular metal squirrel cage blowers as they are not in the fumes.

The air supply for both fans is best if it comes from outside the building so they are not fighting with each other and the hood for air.


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## saadat68 (Mar 16, 2017)

Thanks 
If I must add 3 meter pipe on the roof I think it is better add straight pipe and maybe another time I use this design


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