How best to cap off outside vent from 3 HP dust collector

[Brian Cole]

I opted to start a new thread rather than hijack the recent post on venting outside.

I am installing a used Grizzly 3 HP cyclone. I have removed the Grizzly filter cartridge and will vent the cyclone exhaust outside primarily so I don't have to worry about fine dust getting through the filter cartridge and back into my shop. I plan to open a window on a wall away from the exhaust for make up air when the DC is running. My cyclone exhaust is 8" round connected to a Grizzly 8" diameter muffler. Total length of the exhaust run (including muffler) from cyclone to outside is about 3 feet. Does anyone have suggestions and/or pics of good ways to cap off the outside vent pipe to minimize cold infiltration and conduction when the DC is not running? The 8" exhaust vent will pass through my wood-frame basement wall about 7 feet above grade -the overhead shelter outside is minimal - a 16" roof soffit overhanging two stories above.

I considered an 8" "clothes dryer" type wall cap but am concerned about it restricting airflow and how well the flimsy return spring will hold up to the high flow. Also, a metal cap connected to steel duct through the wall will be a significant source of heat loss through conduction. Does anyone sell a sturdier, less restrictive, non-conducting wall cap? I have seen suggestions for a 45 degree elbow pointing down to keep out precip and an elbow pointing up to minimize noise. Disturbing neighbors is not a big concern since nearest is nearly 1/2 mile away with a lot of trees for buffer. I'm more concerned about noise impact on upper floor living spaces in my house so probably would opt for turned-down exhaust. I could use 8" PVC for the short exhaust duct capped with a PVC 45 elbow (possibly with a homemade spring and flap?) for a thermal break. Also have considered a short length of 8" insulated flex duct between the muffler and the outside as a thermal/acoustic break but haven't thought of a good way to pass 8" i.d. flex duct through the wall (o.d. would probably be at least 12") while getting a good air seal and weatherproof cap on the flex.

Any suggestions will be much appreciated. Thanks.

Brian

[Ken Fitzgerald]

Brian,

2 things to consider.

1. I wonder if getting a screened end would cause problems for the dust to be blown beyond the screen? Would a screen plug? One could consider an unscreened leuvered vent end cap to keep the bugs out.

2. How about using an electrically controlled gate as is sometimes used in autosensing DC systems. The gate would open when the DC comes on. It would be placed between the DC and the wall through which the discharge pipe is going. It would close when the DC is shutoff.

There are several members who discharge their DC outside so I am sure you can get some experienced replies.

[Michael Mahan]

Just now starting to plan a DC with a outside exhaust
I plan on out the garage side wall & then a 90 to face the discharge away from my neighbor & pointed at the back yard I plan on making a oversized muffler running under the roof eves overhang.
weather & cold in my case is not an issue the end of the muffler will under either the over hang or my covered back half of the yard

[Michael Mahan]

I wonder if getting a screened end would cause problems for the dust to be blown beyond the screen? Would a screen plug?

I have 1/2" machine cloth that I plan on covering the tube with to keep out the BlueJays

[Ken Fitzgerald]

Mike, locally I would be more concerned about the yellow jackets invading! They have been horrible here the last 2 years!

[Jerome Stanek]

You have to be careful of screens as they will at as a solid when enough wind tries to do through them

[Rick Moyer]

Are you worried about all the time or just when you're not using the shop. If the latter, I suspect you could put in a blast gate for when you're working in the shop and shut it when you leave. Otherwise I would think an downward pointing elbow would be ok. I also think that possibly you are overthinking the problem, but I could be wrong.

[Brian Cole]

Thanks for the feedback so far. Rick I am concerned more about "all the time." Winters aren't extreme here in the NC mountains, but it was 13 deg F here this morning. I know that a 2" electrical conduit feeding my service panel through the basement wall let in a lot of cold air until I sealed it. So am concerned that an 8" duct could chill the shop even when the DC is not operating. The shop is unheated except for solar gain (house is solar). I'm sure a blast gate would help with infiltration. I was looking for a way to seal the exhaust outside - kind of like the spring loaded flap on a dryer vent. If I can't figure out a tightly sealed flapper rig, I'll use some hardware cloth to keep out the bugs and birds.

[Rod Sheridan]

I would install an 8" metal blast gate................Regards, Rod.

[Michael W. Clark]

I would install an 8" metal blast gate................Regards, Rod.

This would be my thought too, located close to the wall if it is convenient and accessible.

As far as the discharge outside, typical is to cut the duct to have a 45 miter so the open end is facing down and install bird screen. No need to spend the extra on an elbow and losses. If you are still concerned about water, slope the duct down slightly so water cannot run back in the shop.

Another option would be louvers such as used on attic fans. These would add a little back pressure but not much, you would need some type of transition to the louver from your round duct.

[Ed Labadie]

If you keep the blast gates closed when the DC isn't in use, it won't draw air out of the shop.

For a discharge I used 8" pvc and cut a piece of hardware cloth to fit, then held it on with a coupling.

Ed

[Rick Potter]

I have an 8" metal duct going through my stucco wall for exhaust. Always meant to put the hardware cloth over it to keep critters out, but as of now, it has been wide open for 2-3 years with no problems.

The 45 aimed down is a good thing to do. I didn't have to for my situation. If you are concerned about cold conducting through a metal pipe, you might consider 8" PVC for the exit run. As far as the air coming into the shop from outside, the normal blast gates will stop that, but if you are still concerned, adding a gate to the exit area seems a good solution.

I don't know how restrictive that muffler is, but I would consider removing it to see how it works. There is a definite improvement without the filter.

By the way, I have no visible dust or residue on the outside, other than a very thin coat of dust at the end of the pipe.

Rick Potter

[Michael Mahan]

If you keep the blast gates closed when the DC isn't in use, it won't draw air out of the shop.

For a discharge I used 8" pvc and cut a piece of hardware cloth to fit, then held it on with a coupling.

Ed

Ed ,
what your is noise levels like standing outside just under that exhaust duct ? ?
the way you did yours looks slick !

[Ed Labadie]

Thanks, Mike.

Sound level isn't bad, you do know it's running though.....

Ed

[Darren Almeida]

I vent mine through a louvered gable vent. I don't have a pic of it, but it is like this one:

http://www.homedepot.com/p/Cellwood-...0?N=5yc1vZc4mf

I have screen on the inside of the vent to keep bugs and varmits from getting into the outlet pipe when the dc is not running. At first I was concerned about the screen blocking the airflow, but then when you think about it the hepa filter the dc normally discharges into is way more restrictive. I have't had any issues with it. Only the super fine stuff goes out that vent so I haven't even had to clean the screen.

I put 2 layers of 1.5" rigid foam insulation around the vent pipe and screwed it right to the wood around the gable vent. That cuts off the air flow from the rest of the gable vent. So the only cold air that gets in is through the vent pipe itself. I just make sure to keep all my blast gates closed when I am not using my dc and I dont really have too much of a problem with cold air getting in. Yes, it is colder than running / venting the dc indoors, but I am not going to deal with having that in my shop. I guess I should have mentioned up front, my dc is in a bump out shed that is off of my woodshop. I love the set up. Quiet and no cleaning filters.