Steve:

1.5" Hg is about 2 psi - that's a lot of suck.  Also, it is specified at the machine.  Your 1600
cfm blower is going to try to pressurize the exhaust ducts.  (Imagine hooking a compressed air
hose into a vacuum line.)  You might want to look at alternative exhaust configurations and make
sure that your HVAC contractor or engineer is familiar with this type of work.  (Commercial
contractors don't always have the experience to handle this type of design.)  I'm not surprised
at the proposed cost, given what you're trying to do with one fan.  You may find that multiple
exhaust fans will provide better process control and lower total cost.

Best of luck,

Don Vischulis
[log in to unmask]

SteveZeva wrote:

> Hello Technetters!
>
> snip -------------------------------------------

> I wanted to exhaust 4 machines from one exhaust fan up on the roof. There
>  will be a Heller 1700 convection oven which the specs say I need 500 cfm, a
>  Soltec Prisma wave solder (I can't remember what kinda' suck it needs, the
>  spec is on my desk at work), a waste water evaporator coming off a ultrasonic
>  stencil cleaner (which has it's own exhaust blower rated at 1600 cfm so it
>  really won't add a whole lotta load), and last but not least our Trek
>  Triton...and that seems to be the culprit behind the big buck expenses.
>
>      Trek spec's say that it needs a -1.5 in. hg. negative pressure in the
>  duct, the HVAC company that quoted us says the fan we currently have doesn't
>  suck enough, but I think it sucks pretty good. They want to completely replace
>  the fan we have which means a crane rental, and cutting a different hole in
>  the roof with all the associated work that goes along with that.

snip the rest ---------------------------------------

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