PDA

View Full Version : Laser Vent Question



Jeff Belany
05-19-2011, 3:35 PM
I'm moving into another building next month. Better location and plan to add a Gift Shop that will handle consignment sales for local artists and artisans in addition to selling the laser items.

My question -- I am looking at venting my laser out through the roof with a plumbing stack that I will have put in when the plumber adds a new bathroom. Has anyone done this? Any issues I should be concerned about? As far as my thinking it should work OK. Just checking with the pros to see if this will work.

Any feedback will be greatly appreciated.

Jeff in northern Wisconsin

Michael Hunter
05-19-2011, 5:20 PM
Clever way of disguising the exhaust!

Will the plumbing stack be made of plastic pipe? Bit of a fire risk if it is.

Paul Brinkmeyer
05-19-2011, 5:59 PM
I have gone through the roof, 4" vent and rain cap on top. only one problem came up. Just make sure it is higher than any AC units or other things that might be bringing air in. (Yes, I learned the hard way on that one.)

Chuck Stone
05-19-2011, 8:20 PM
I wouldn't think it would create any problem, but I'm no expert. As mentioned,
making sure that the vented air doesn't get sucked back in (to your place or
someone else's!) would be the main concern for me. Secondary concern would
be that a vent can also let air back in when nothing is pushing the air out,
so it should have some way of closing when not in use. Otherwise, your laser
might be very cold when you come in in the morning.. and the room it resides in!
(DAMHIKT)

Jeff Belany
05-20-2011, 10:27 AM
Thanks for the input. My exhaust fan (homemade furnace fan) has a blast gate on it already to stop the cold coming in. I'm pretty sure it will work. My main rason for asking was in case someone else tried it and it failed. I'll know in a month or so when I move.

Jeff in northern Wisconsin

Richard Rumancik
05-20-2011, 11:02 AM
I am not a plumber, but my understanding is that the stack is intended to vent sewer gases from the plumbing fixtures to the roof. It also provides pressure equalization so that water flows down drains properly and doesn't get restricted due to the vacuum effect created when the water drops in the pipe. By pressurising the vent stack with a blower, you would be reversing the flow and pressurizing the plumbing fixtures. I would expect that you would get some airflow out of the drains which would smell pretty bad. It would probably blow the water out of the traps in the sinks and maybe your toilets would even bubble. I doubt that the plumber would agree to it as it would likely violate every building code.

You could consider a second stack although that might look a bit ugly on the roof. Perhaps there is some way to make a concentric stack that would look okay, with the exhaust air on the outer ring of the plumbing stack. This would look something like a concentric vent on a gas furnace. (If you have not seen what that looks like, Google for images of "concentric vent"). With this system on a gas furnace, the exhaust air and fresh air go through what appears to be a single pipe (one hole in the wall). But you need to ensure you can get the volumes through without backpressure so you will need large tubing.

Dan Hintz
05-20-2011, 11:41 AM
Richard,

I got the impression it would be stack-like, not using the same stack.

Sandy Henry
05-20-2011, 11:49 AM
Running YAG laser in factory & they connect my exhaust to bathroom exhaust. When laser was not running, & after lunch (at White Castle) the guys kicked on the bathroom exhaust...less resistance to laser than to out doors...Thought I was gonna DIE!!

Dan Hintz
05-20-2011, 12:02 PM
Running YAG laser in factory & they connect my exhaust to bathroom exhaust. When laser was not running, & after lunch (at White Castle) the guys kicked on the bathroom exhaust...less resistance to laser than to out doors...Thought I was gonna DIE!!
Sad... and funny, at the same time :D Be glad it was only White Castle and not Taco Bell.

Richard Rumancik
05-20-2011, 12:35 PM
Richard, . . . I got the impression it would be stack-like, not using the same stack.

If that is the case then I don't understand the question - because if it is a completely separate stack, then I don't see how this is different than any other exhaust system. Since he said it was part of the bathroom install I just assumed it was the toilet stack (he called it a plumbing stack). I hope I was wrong as to his plans . . .

People are sometimes creative trying to multiplex exhaust systems (e.g. trying to exhaust 2 bathrooms using one vent). Could be done I suppose, if the right dampers were involved, but if no dampers, one fan could force air into the other room. If two fans/blowers are running at the same time who knows what will happen - it would be two non-identical blowers in parallel which is often an unstable system.

Jeff Belany
05-20-2011, 2:56 PM
Just to clarify. This will be a separate stack. I just mentioned it with the plumbing since the plumber will install it at the same time he puts in the new ADA bathroom since he will be on the roof anyway.

Jeff in northern Wisconsin

Joe Pelonio
05-20-2011, 8:01 PM
That will work then, but use smooth metal duct so less debris will stick to it.

Make sure the fan is strong enough. One suggestion, a typical chimney cap is not the best way to go as your debris will hit it and bounce around, allowing any wind more opportunity to blow it into neighboring businesses. Use a 45 at the top, aimed in the direction with the least sensitive area, such as the parking lot. Then do just enough of a cap to keep rain from going in. When I was in a business park I had to do a lot of adjusting before I got the complaints to stop. The worst was a store that had no A/C and opened their window on a hot day, with a fan in front of it sucking in my fumes! :(

Dee Gallo
05-20-2011, 9:02 PM
I'm no plumber, but if I was doing this, I'd put a cleanout trapdoor on the bottom. There is bound to be stuff that falls back down a vertical chimney type vent.

Craig Matheny
05-28-2011, 7:08 PM
I have this set up and no issues I ran metal duct work for 10' to a 1hp blower then abs 4" pipe out the roof works like a charm put a 90 and 45 on top to turn it down and at an angle so wind and rain not an issue

Jarami Reid
07-25-2011, 7:07 PM
Having a bit of trouble of my own, but I'm trying not to hi jack this thread.

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.

Dan Hintz
07-25-2011, 7:16 PM
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
07-25-2011, 7:42 PM
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
07-25-2011, 8:23 PM
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
07-25-2011, 9:01 PM
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
07-25-2011, 11:21 PM
. . . 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.