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James Terry
06-25-2010, 12:55 AM
I have been using a temporary exhaust pipe and am ready to move to something better. I think I will take the 4" pipe up through the ceiling and out through the roof with a good amount of rise to it. Being in a neighborhood, I would like to do my best to blast the odors up and away from myself and neighbors. A typical roof vent would blow up and out under a cap to protect from rain, so the airflow is disrupted at that point and smell will stay closer. I want my pipe to blast wide open straight up to take full use of the velocity of air. So what are my options for such a thing? Do I top this off with a weighted flap that closes when off? Is PVC a better idea over metal? Is this just a bad idea? What is your opinion on placement of the blower; safely in reach or hidden up in the hot dusty attic closer to the outlet?

My roof is composition, not wood, so hot debris and sparks should not be an issue.

Michael Hunter
06-25-2010, 6:49 AM
Metal pipe!!!
Hopefully you will never have a fire in the laser, but if you did, you wouldn't want the fire to spread from the vent pipe.

I too have the "open top - rain getting in" problem and would be interested in how others solve it.

Dan Hintz
06-25-2010, 10:49 AM
Leaving it wide open to rain is a bad idea. There's little restriction to putting a permanent "roof" over the pipe as long the roof is far enough away from the opening. I'd place the cap about a foot off of the top, and make it really wide so rain doesn't trickle in during hard winds... think along the lines of the palm frond hats worn by pickers standing in rice paddies all day.

Terry Swift
06-25-2010, 11:03 AM
James,

Everything I've read says 4" PVC pipe is fine and you need to make sure any bends connections use plastic piping. I'm not sure how hard it would be to do a metal one; but again - I was told metal was not a good choice due to corrosion caused by certain materials - not sure which ones - just the precedent from others. I put my exhaust fan up in my attic on the crossmembers and ran a tube up to my wind turbine vent on the roof. I don't think I raise that much of a stink with my neighbors that way and I don't have to worry about rain, etc. getting in.

Maybe adding a 45 degree joint at the top of the pipe with something like a dryer vent would work for you too. The louvered types only open when venting is going on and when on the 45 degree pipe it would be standing in the vertical position to keep the louvers closed when not in use.

Mike Null
06-25-2010, 10:44 PM
I would use metal just to be sure there was no fire hazard. (pvc will be quieter) I vent mine through a wall using the the dryer cap which has a screen to keep out bugs and a flap that closes when not in use.

Larry Bratton
06-25-2010, 11:16 PM
Mine vents using two flexible pipes(the EXT has two) into a 1 straight metal pipe, through the wall to my exhaust fan I have outside. The exhaust fan is housed in a Tractor Supply plastic dog house and connected to a weatherproof electrical outlet. Inside wall switch to turn it off and on. Noisy though, fortunately I don't have any close neighbors.

James Terry
06-25-2010, 11:26 PM
So you think there is no need to have a riser or a vertical exhaust? My thinking was that when doing acrylic or rubber, the velocity would help take the vapors higher quicker, but I cant seem to find a pipe cap with gravity damper that is fully vertical. If such does exist, it may need a wind shield surrounding it that is open at the top for the flap to open through.


So most of you folks are using 4" wall or rooftop dry vents? I found this style which looks nice and low profile but it ejects everything down against the roof. So vapors lose speed immediately but I suppose if installed at the top of the roof, there would be plenty of space for vapors to rise and not be picked up by neighbors unless its windy.

http://www.ntsupply.com/images/product_content/dryercapinset1.gif

James Terry
06-26-2010, 12:12 AM
I think what I have been looking for might be an upblast exhaust blower which you often find on restaurants, paint booths, chemical plants, labs... I guess they somehow allow exhaust to be blown at high velocity straight up while also blocking rain.

The problem is that I havent yet seen one of these that does not have a high speed fan built into it. I think I'd like to simply find a small upblast vent cap if it can be found.

Maybe Doug G will have some crazy creative ideas here for me. :) Gravity dampers on the end of a coffee can...?

greg lindsey
06-26-2010, 12:17 AM
I've been using 4" PVC for years, never any problems. I took a self closing dryer vent and mounted it to a 90 coming off the straight, never rains in it and no birds trying to get in.

Joe Pelonio
06-26-2010, 12:20 AM
Your location of the vent in relation to the neighbors is key, even up on the roof, winds can whip the fumes around so be aware of which way they normally blow in your area. If the fumes get under any eaves, they will be trapped there and be more noticeable.

I vent out the side of my second-story shop and have had no complaints in over 3 years now, but it goes out the side which faces a side street and not toward any other homes. The nearest window is the house behind us bathroom window which is rarely open.

I had a lot more problems when I was in a commercial/industrial complex.

Mike Null
06-26-2010, 8:27 AM
My neighbors are within 50 feet of my exhaust and I've never even had them acknowledge that I was venting anything.

But I don't do rubber.

Doug Griffith
06-26-2010, 7:50 PM
I use 4" pipe that runs straight up the side of my house and about a foot above the eaves. Being in California, it doesn't rain much. When it does, I attach a home made gravity damper with a heavy duty rubber band. It hasn't failed me yet.

James Terry
06-26-2010, 11:42 PM
I found one that looks exactly like what I want but I cannot find it for sale. I have emailed the manufacturer. Perhaps someone on here has seen this somewhere.


Dampered Weather Cap
Exhaust pipe termination cap with a backdraft damper. Dampers close automatically when exhaust fan is shut off. Dampers are pitched to close to let rain or snow runoff outside of duct.. Available in all diameters.

http://bhvfab.com/products/Industrial/images/idpic21.jpg

John Barton
06-26-2010, 11:45 PM
I use 4" pipe that runs straight up the side of my house and about a foot above the eaves. Being in California, it doesn't rain much. When it does, I attach a home made gravity damper with a heavy duty rubber band. It hasn't failed me yet.

I love it! I really like to see when people make parts with the laser for the laser.

I will make a new thread when I get back in the shop about my magnetic focus tool - basically a magnet between two pieces of acrylic so it stays on the laser and easy to find. We should have an ongoing thread about tools and jigs made with the laser - (probably exists already so if someone knows the link please point me there)

Doug Griffith
06-27-2010, 12:23 AM
That looks OK but how does it prevent rain from entering the pipe?

Dan Hintz
06-27-2010, 5:27 PM
I was told metal was not a good choice due to corrosion caused by certain materials
Anything that can cause corrosion in your exhaust pipes is going to do the same to your machine... in other words, you should avoid those materials at any cost anyway.