Too Much Ventilation? -box fan with hood

[Judi_B]

I got a Piranah for my birthday and spent the last two days setting up a new work station ---yea!!! no more waiting for good weather to torch outside. But I can't torch yet because I can't get a steady flame :sad: There seems to be too much ventilation! I have a "barley box" type set-up with an open back. I used aluminum flashing to cover the back leaving an opening the size of a box fan. The hood gets pushed up aganist the box fan, which is braced in a window. I have good make-up air from an open window (more than 10 ft away from the exhaust window). Because of the height of the window, the fan is at bench level, so the make-up air is flowing past me, over flame and out the window. The flame wavers back and forth and changes when I move my hands. It's a nice steady flame when the fan is off. Has anyone else been able to get a box fan/hood set-up to work?

I also tried using the fan unit from a portable dust collector. I removed the filters so its just the three six-inch fans mounted in a retangular metal box. It is variable speed up to 750 cfm. I put it in the window, used more flashing to make the hole in the back of the hood the right size and pushed the hood up against the fan. Since I didn't have any incense, I turned the oxy down enough to get a sooty flame to test the ventillation. At 750 cfm all of smoke is rapidly pulled out the window, but the flame wavers. If I turn the fan down to where the flame stays steady, some smoke accumulates in the top of the hood and then spills out the front (I have a 10 inch baffle on the front) ](*,)

Help please, I want to torch :cry:

[MikeAurelius]

The problem is the box fan - it is too "big" as in size big. The CFM's may be correct, but the diameter of the fan is causing a large area of disturbed air.

This is why ducting with 8" duct to a fan and then out a window or other opening is the preferred method of exhausting air.

[Judi_B]

Soooooo ... does that mean that the set-up shown in this link (http://www.artglassanswers.com/forum/viewtopic.php?t=90) using a box fan at the back of a hood isn't really feasible? :???:

I think I see a trip to Home Depot in my future :roll:

[MikeAurelius]

I'm not a member of that group so I can't see the pictures, but in general, backing a box fan up to a hood doesn't work real well, as you've discovered. The issue, as I pointed out (and as you have witnessed first hand), is one of air disturbance.

Box fans are great room fans - heck, I've got one running right now on the 3 season porch to keep it warm for the real estate people doing open house.

But they are not meant for local ventilation. That's not to say they cannot be used, as long as you are willing to put up with a dancing flame.

[Dale M.]

Soooooo ... does that mean that the set-up shown in this link (http://www.artglassanswers.com/forum/viewtopic.php?t=90) using a box fan at the back of a hood isn't really feasible? :???:

I think I see a trip to Home Depot in my future :roll:

If you read whole series of messages again, all the emphasis is on a blower and ducting, using a box fan is only one option...

Dale

[Judi_B]

Dale,
I did read the the whole series and there is a lot of great information there! I liked the plan with the box fan because I already had everything and only needed to buy a little aluminum flashing. Since the plan comes from a good source (I really do trust you guys in these matters!), it looked like a good alternative to the ducting. Is there something I'm doing wrong, or is the box fan not really a feasible alternative? It's awfully hard to work with a "dancing" flame 8-[

[Dale M.]

Al lot will depend on the fan design and at the speed you have to run it go get a good airflow.... I have not actually tested that particular configuration, so you will have to rely on Bill Brachholds comments on how well it works.

Dale

[Judi_B]

Thank you Mike and Dale for your help and comments. I finally got good ventilation by ducting from the back of the hood at the top to the dust collector fan in the window. By moving the exhaust towards the top of the hood I was able to run the fan at a lower speed and not have fumes (by the smoke test) accummulating in the top and spilling out. I now have a pretty steady flame. It would probably be better to actually be pulling out from the top of the hood, but that will have to wait for the next incarnation of this ventilation system :roll: For now, I can finally play with my new Piranha :grin:

[MikeAurelius]

Excellent! Good for you!