Vent System adcie

[docdana]

OK, I've read a lot of info about vent systems & I think I understand CFM's, Velocity Pressure, Static Pressure, & Loss Factor. I have calculated the CFM's I need for the design I came up with. My situation is this:

Torch on desk in front of basement window which is glass block with a 10X7 inch screened opening (pivots up & in but can be removed). I'd like to not use any ducting and just build a "barley box" on my torch bench and have the exhaust fan directly in front of the window to vent out. I have the make-up air taken care of (vent from other window 20 feet away coming up behind desk into "back" of barley box.

Based on this design I'm coming up with 960 CFM. Am I missing anything?

Here is a drawing to clarify (LOL, the way I draw it might confuse more than clarify!) Any & all advice, ideas, criticism appreciated!

43778

Dana

[MikeAurelius]

Dana - you are going to have to use ducting. There's no way around it.

Just placing the exhaust fan in front of a small opening is going to result in a lot of blow-by.

The opening is large enough to handle your requirements, but you will have to duct it, otherwise, you will probably only be pushing about 50% of the air out the window.

[docdana]

Thanks Mike, that's kind of what I thought. I really won't have much of a "run" so I think I'll still be OK with that CFM exhaust but I will put the duct into the window opening and seal with a rubber gasket (the duct work that goes from round to a rectangular opening should be perfect). Any other suggestions? Thanks much for your help.

Dana

[MikeAurelius]

Nope that should be fine -- you may want to remove the screen and replace it with something with a larger mesh - on the order of 1/2" or so.

[bead crazy]

When you have your replacement air coming up to the table like that do you need a fan to push it up or is the fan in the vent pull the air up?
Lori

[Just Nancy]

Lori,
As I understand it replacement air comes in without an extra fan. It comes in because other air was moved out.

Also no matter how many cfm the fan 'can' exhaust, it 'will' only push out as much air as is available in make up air. So enough make up air is just as important as cfm on the fan.