Box enclosure with exterior exhaust for HF Dust Collector

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Forum topic by Andrew posted 10-11-2011 05:09 AM 4480 views 0 times favorited 11 replies Add to Favorites Watch
View Andrew's profile


3 posts in 3505 days

10-11-2011 05:09 AM

Hello! I’m new to LumberJocks and have been enjoying wealth of information here. I’ve been looking for a dust management solution, and based on what I read here, I picked up a slightly used HF 2hp Dust Collector.

I was originally thinking of getting one of the Wynn 35A cartridges based on reviews, but I’m wondering if it makes more sense to build a box around the bag filter and exhaust it outside the building. I would connect the box to a window with some flex tubing. I was thinking 6” min dia for the opening to the outside

The concerns I have heard by exhausting outside are heating or cooling the shop too much and blowing dust to a neighbor. It is pretty mild here, and uninsulated shop is never too hot or too cold. And the nearest neighbor is >300’ away.

Are there other concerns about building a box around the filter bag? It seems like the standard 30micron bag would be fine in this application. I would expect 3-4” of clearance around the bag would be fine.


-- Andrew, Santa Cruz, CA

11 replies so far

View Gary's profile


9419 posts in 4517 days

#1 posted 10-11-2011 06:06 AM

Hi Andrew. I have no idea for you…just wanted to say welcome to the site. Hang around, you’ll get answers

-- Gary, DeKalb Texas only 4 miles from the mill

View Sawkerf's profile


1730 posts in 4153 days

#2 posted 10-11-2011 06:29 AM

If I understand your plan, you want to box the upper (filter) bag and vent it thru a window to the outside. If that’s right, what will drive the air from your box into the 6” flex and thru the window? Without some kind of driving force, you’ll just build up a bunch of dust in your box.

Also, that 6” flex will actually reduce the air flow thru your system (backpressure).

-- Adversity doesn't build reveals it.

View Sarit's profile


552 posts in 4224 days

#3 posted 10-11-2011 07:37 AM

Sawkerf, I think the same air pressure that’s forcing the air through the bag’s 20 micron pores will push the air through the 6” flex and out the window. Remember, CFM in = CFM out (as long as its sealed).

Andrew, I think your plan will work.
Alternatively, I would suggest building something like the Thien separator and directly venting the exhaust outside without the bag. There is a design out there that incorporates the Thien baffle directly onto the ring that your bag attaches to. From there you simply need a donut shaped plywood cover to seal the top of the ring (w/o the bag) and adapt it to your 6” flex that goes out the window. Only the very fine (flour like) particles seems to escape a properly built thien separator so I don’t think you’ll have any problems shooting those out the window.

View redryder's profile


2393 posts in 4186 days

#4 posted 10-11-2011 08:08 AM

Sending it over to the neighbors is always a good way to start a conversation….......

-- mike...............

View Blackie_'s profile


4883 posts in 3597 days

#5 posted 10-11-2011 01:43 PM

Andrew, not sure if this application would work in your case but yes these CD’s move a lot of air from what you are saying you are not ACed? I have a stand alone shop and added an outer storage for my DC and also air compressor as my shop is ACed so I added insulation to the outer storage. I have a 24” window that separates the shop from the shed and added an AC filter over the window to keep dust out and cool air back in.

Here are pictures of my setup.

-- Randy - If I'm not on LJ's then I'm making Saw Dust. Please feel free to visit my store location at

View MrRon's profile


6024 posts in 4328 days

#6 posted 10-11-2011 11:41 PM

I have the HF 2 hp DC. I decided to get rid of everything, except for the motor and fan and direct the exhaust to the outdoors. I put a 55 gal drum between the DC and the pickups. so that large chunks and heavy sawdust goes and settles in the drum and only the light dust passes throught the DC.

View Boneski's profile


143 posts in 4217 days

#7 posted 10-12-2011 12:50 AM

Andrew I’ve been thinking about this for a long time now and once I buy my own house with my own workshop I’m planning on doing something similar to Blackie, but more of a lean to version. The plan is for it to be air tight with the only air outlet through a flat removable filter element (room filter style). After that maybe a baffle that can be opened or closed to choose if air is vented back into the shop of outside.
I think it would be fairly easy to build something like this inside of the shop too, space permitting.

-- Blinded by brilliance

View Sawkerf's profile


1730 posts in 4153 days

#8 posted 10-12-2011 01:03 AM

Sarit -

The pressure will definitely cause flow thru the 6” duct, but only enough to stabilize the pressure. Most of the dust will stay in the box since the flow in all parts of the box won’t be great enough to carry it to the duct.

To get all of the dust out the duct, the air flow must be toward the duct and have enough velocity to carry all of the dust with it.

-- Adversity doesn't build reveals it.

View elkhunter's profile


16 posts in 5162 days

#9 posted 10-12-2011 06:13 AM

I took a slightly different approach, I built my “box” on the outside of my stand alone shop. The noise and dust (although a small amount of dust) are outside. My 1 1/2 horse collector is wired through a heavy duty (high amp) switch so it is easly turned on or off from inside. It does suck heat from the building, but I heat with wood so I throw another log in the wood stove. I used drier vent ducting and flex hose and flex hose fittings (Ys, blast gates, and so-on) to make a permanent conection to each machine. Just inside from my dust collector is a 2 stage separator (inside for easy emptying). I chose 4” ducting for my set up, and have had very few problems.

-- John of Idaho

View Andrew's profile


3 posts in 3505 days

#10 posted 10-12-2011 08:21 AM

Thanks for the great ideas everyone.

I did a preliminary experiment making a Thien separator. W/o the separator or the filter bag, a huge tornado of dust shoots out the top. Adding the separator, but still with no filter, almost nothing visible comes out. So Sarit’s suggestion looks viable. Note this is only testing with materials already in the bag, and does not account for an inflow of dust and debris from the tools.

BTW, I got to use my new table saw while making the standoffs for the separator. What a dream! (SawStop PCS 3hp—totally overkill for this little task).

-- Andrew, Santa Cruz, CA

View Sarit's profile


552 posts in 4224 days

#11 posted 10-13-2011 12:44 AM

I have the PCS also. Its a great machine. I also live close to the SF bay area not too far from Santa Cruz. There’s seems to be some saw mills in your area so you might be able to score some cheap wood. I think I found them in Craigslist.

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