Laser Vent Question

[Dan Hintz]

won't "pushing" air up through a stack decrease the effectiveness of you exhaust fan. Wouldn't it be better to put the fan on the roof and pull the air through the exhaust pipes.

Sure, but it beats the cost of running electrical to the roof, covering the fan from the elements, etc. If performance is "good enough", why spend the extra dough.

[Craig Matheny]

I would say yes if it is over a large distance, but then again it all depends on the blower you have and your specs for the laser. I bought mine to handle more then the laser needs helps take the warp out of wood and blow the smoke away from the area.

[Richard Rumancik]

Jarami, why do you feel it would be more efficient to have the blower on the roof? Did you see that in a blower spec? There are sometimes reasons for placing the blower on a roof: it moves the noise; the blower doesn't take shop space; it means that the ducting is mainly at low pressure (won't leak toxic gas) etc. But I do not see how it would be more efficient. Either you have the duct resistance on the intake side or on the exhaust side. I doubt that you will see a signficant difference in operation. I do have my blower far away from my machine, actually in the "attic" of the building, but it was not because I expected improved performance that I did it that way.

[Jarami Reid]

Hi Richard,

I'm feeling very understood right now. thanks all for responses.

I'm asking more than telling here - from what the HVAC experts (sarcasm) in my life have told me I don't want to put my fan too far away from the machine - I've heard the "short straw, long straw" analogy a couple times now.

What I'm starting to think is that extending the exhaust run is gonna decrease my pull no matter where I put my fan. The end, middle, beginning whatever.

[Richard Rumancik]

. . . I've heard the "short straw, long straw" analogy a couple times now. What I'm starting to think is that extending the exhaust run is gonna decrease my pull no matter where I put my fan. The end, middle, beginning whatever.

Hmm . . . if someone told you that having a "short straw" on the exhaust end of the blower is better they are forgetting that there will be a longer straw on the intake. Gravity does not usually play a large part in air systems although sometimes it needs to be included. But if you have to lift the air 15 feet to the roof the blower needs to expend energy to get it there regardless of where it is in the path.

Air systems do not always behave like electric circuits as they have more non-linear behaviours. But in this case the blower is rather like the "battery" and the ducts act like series resistances. It is a closed circuit, because air is drawn in at atmospheric pressure and exhausted to atmosphere. In an electric circuit it would not matter where the battery is in a circuit having two (or more) resistors. I don't think you will see a difference with the blower placement either. So yes, I would say your conclusion is correct.