My outside-exhausting DC w/ baffle

[Dan Friedrichs]

I just finished setting my DC up to exhaust outside, so here's some pics.

Inside the grarag...*cough*cough* shop, there's 6" ASTM 2729 pipe to each tool. The pipe was just fitted together, and screwed through the fittings (no glue), so I can take it apart and re-arrange later (if wanted).

The main line goes through the "floor" into the crawlspace below the house. There, it's sucked into a 2HP Griz collector. I modified it by adding a Thien baffle below the existing input port, and by mounting a 6" piece of PVC to the top "outlet" (where the top bag would usually sit).

From there, the exhaust runs through another piece of 6" PVC to the wall of the crawlspace, where it goes through the wall, and vents outside the house.

I had to use 90* fittings on the exhaust because there wasn't room for 2 45*'s.

The Thien baffle is excellent. If you look at the last pic (showing the outlet on the side of the house), you'll see there's no dust on the rocks below (well, there's a little, but it's from sawing the 6" hole!). It all stays in the bag.

I'm going to replace the bottom bag with a plastic one, just so I don't end up with a fine layer of dust on everything in the crawlspace.

I'm also going to re-arrange the connections on the DC so that it hits the baffle/bag BEFORE the impeller, just incase I suck up any nails.

[Bruce Page]

Won't you be pushing all your heat outside come winter time?

[David Christopher]

Dan, thats pretty slick....I have the same DC..mine sits behind the shop. I took off everything and dump strait into a fox wire basket about 4 ft square....no bag no filter no seperater...6" from DC output to wire basket

[Dan Friedrichs]

Won't you be pushing all your heat outside come winter time?

Yeah, but my garage isn't heated, so I'm OK with it. My schedule rarely leaves me much time for woodworking during the winter months, anyways.

[Matt Benton]

Dan,

Unless you've done it somewhere else, you may want to put some wire mesh over the outlet to prevent small critters from getting into the DC...

[Ed Garrett]

Dan,

I'm pursuing a similar setup. How loud is the air blasting out of the exhaust port???

Sincerely,
Ed Garrett
Tallahassee

[Dan Friedrichs]

I'm pursuing a similar setup. How loud is the air blasting out of the exhaust port???

Good question. I have a neighbor whose backyard is about 20' from the exhaust port, so I was concerned about that. I'd estimate that it is maybe 1/2 as loud as a shop vac, or maybe 4x as loud as a dryer vent. It's definitely noticable, but I don't think it's loud enough that anyone would complain.

One thing you might consider is using something other than PVC for the exhaust piping. If you could find some of that flexible, insulated tubing they use to pipe HVAC around, I think that would be ideal. It's insulated, which might help deaden some of the noise, and it's flexible, so you could coil it a little before routing it outside, which would definitely deaden a good deal of the noise. The more the air as to turn corners, the less loud it will be.

[Jim Kountz]

So you have to crawl under the shop to empty the bag? Hows that working for ya?

[Myk Rian]

So you have to crawl under the shop to empty the bag? Hows that working for ya?

That's what I was wondering. I would rather duct the whole thing straight off the fan to the outside, and into a catch box. Just bypass the bags entirely.

The more twists, turns, etc. in a duct, the more noise will be generated by the turbulence. A smooth, straight duct is the most silent. I have 35 years experience on that matter.

[Mark Norman]

That's what I was wondering. I would rather duct the whole thing straight off the fan to the outside, and into a catch box. Just bypass the bags entirely.

The more twists, turns, etc. in a duct, the more noise will be generated by the turbulence. A smooth, straight duct is the most silent. I have 35 years experience on that matter.

+1, more turbulance = more noise.

I would also just pipe the stuff to the outside into some sort of containment such as a 55 gallon drum.

[Dan Friedrichs]

Ideally, it would just all go outside, but I live in a suburban neighborhood where that wouldn't fly.

Emptying the bag isn't a big deal - the crawlspace is actually under the house, which is higher than the garage, so it's only about a foot or so below the garage floor. Plus, I don't fill bags that often

I'm no noise expert, but it seems like there's two completely different things being talked about here:
First, the noise from the airflow itself. Certainly, more turbulence makes more noise.
Second, is noise generated at the impeller. In order to deaden this noise, you'd want to make the path non-straight, with massive interruptions in the path to absorb the sound energy. That's why people build "Z" shaped return ducts from their DC closets.

[Myk Rian]

Ideally, it would just all go outside, but I live in a suburban neighborhood where that wouldn't fly.

That's why the collection box.

I'm no noise expert, but it seems like there's two completely different things being talked about here:
First, the noise from the airflow itself. Certainly, more turbulence makes more noise.
Second, is noise generated at the impeller. In order to deaden this noise, you'd want to make the path non-straight, with massive interruptions in the path to absorb the sound energy. That's why people build "Z" shaped return ducts from their DC closets.

The impeller noise will still be transported down the tube. You won't get away from that, except by using a collection box to act as a muffler. The Z shaped duct will do nothing but impede the airflow, hence, less flow at the tools.

[Dan Friedrichs]

That's why the collection box.

No, that's what I meant - I would not get away with setting a collection box outside. The HOA would declare that it didn't match the decor

The impeller noise will still be transported down the tube. You won't get away from that, except by using a collection box to act as a muffler. The Z shaped duct will do nothing but impede the airflow, hence, less flow at the tools.

How does a collection box muffle sound? I think you're thinking of this like a car muffler, but it's entirely different. In a car, noise is created by the expansion of the air, thus the muffler acts as a place for the noise to be produced and absorbed prior to leaving the system. Here, the noise is not generated by the same means.

As the noise energy is transmitted through the tube/duct/whatever, the more barriers it encounters, the more energy from it is absorbed.

What you're suggesting is that if I place a speaker at the end of a straight piece of PVC pipe and measure the volume, then repeat with a pipe with several bends in it, I'll hear the same volume with both. Again, I'm no expert on this, but that seems intuitively wrong.

[Terry Stellman]

Dan,

I have the same dust collector and have wanted to vent mine outside also. Could you explain or better yet post a picture of what the top looks like that you connect to your 6" vent? How did you seal it? Thanks.

Terry

[Dan Friedrichs]

Dan,

I have the same dust collector and have wanted to vent mine outside also. Could you explain or better yet post a picture of what the top looks like that you connect to your 6" vent? How did you seal it? Thanks.

Terry

Sorry, I didn't take a picture of the top. It's really simple, though: I cut a piece of MDF into a circle that sits on a ridge along the top (if yours doesn't have a ridge, some bolts into the sides for the MDF circle to rest on would also work), and cut a 6" dia hole in the middle of that, which the PVC pipe goes into. I caulked the joints just to make sure no fines would escape.

If you're concerned about the stability of the piece of PVC sticking out of the top (ie - how to securely attach it to the MDF circle), there are lots of options:
-Use thick piece of MDF/ply and glue between the pipe and the MDF
-Heat the piece of PVC, then flare it out below the MDF
-Drive some screws through the pipe into the MDF