This is a branch of engineering in itself with application mainly in the 
machine tool industry where the cutting tools generate much heat which 
vaporize liquids, and also in the HVAC industry where heating/cooling at 
doorways to keep the conditioned air in and unconditioned air out. 
Considerations include ambient airflow (drafts) and air 
velocity/direction at air inlets/outlets. Sorry can't offer more help, 
probably the ASHRAE manual would offer some guidance, it's the turf of 
some mechanical engineer type.

Forrest W Christian wrote:
> Jinx wrote:
>   
>>> The specs for the current version of this machine spec 300CFM
>>> or 500m3/h.    The Manual says "Use a 400CFM (150m3/h)
>>>       
>> 300cfm = 510m3/h => 400cfm = 680m3/h
>>
>> 88cfm = 150m3/h
>>
>>     
>
> I think I pointed that out.
>
> I really think that someone was careless when doing the manual.  I think 
> the correct figure is "300CFM (510m3/hr)", which is pretty much 
> consistent with all similar machines that I've found, and their current 
> spec sheets for this model on the web site.....  I can see how someone 
> could typo a 4 for a 3, and transpose the 1 and the 5.....
>
> It should be noted that modern range hoods are easily in the 3-400CFM 
> range, so it's not unrealistic to believe that a 12" wave solder machine 
> wants that much airflow.
>
> My current theory is that I'm going to have to end up with a 12" duct 
> and a 12" duct fan (650CFM, Free Air) to do most of the path, and then 
> choke it down to the 4" right next to the machine, and hope that I end 
> up with sufficient airflow...
>
> -forrest
>   
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