Air return for DC in closet

[mark mcfarlane]

I pan on putting my DC in a large closet and use 25' of flexible duct to return air to the shop. Inlet on DC ( not purchased yet, probably a 3HP Oneida system) is probably going to be 7.

Do you think a 10" return duct is enough, thats around 80 sq inches.

[Greg Parrish]

I pan on putting my DC in a large closet and use 25' of flexible duct to return air to the shop. Inlet on DC ( not purchased yet, probably a 3HP Oneida system) is probably going to be 7.

Do you think a 10" return duct is enough, thats around 80 sq inches.

Mark, I would probably call Oneida on that one as they know their machine best. The 3hp is great but they may even recommend a different machine or motor size based on that intended usage.

ps - if you can wait to purchase Oneida usually has a sale around July 4th as I think that's when I bought mine. Saved quite a bit by buying during one of their sales too.

[Wayne Lomman]

Mark, you will need more than that. I can't give you an actual size but you have to avoid any possibility of back pressure which will restrict the efficiency of the machine. Cheers

[Lee Schierer]

I think if I were going to do this I would build an opening that would hold at least a 20 x 20 furnace air filter and put a Merv 11 or higher filter in it. This would catch anything that gets past your DC system filters.

[Andy Giddings]

Mark, see attached from the ClearVue forum where someone with a CV1800 is asking the same question. Advice seems to be 8 inch diameter is enough for their blower which is 5HP 1442CFM rated. As you'll already be cleaning the air down to 0.5 micron I don't see a need for additional filtering after that. You will need a plenum if you are doing this to reduce noise http://www.clearvuecyclones.com/foru...n-air-question

[mark mcfarlane]

Thanks Greg,Wayne, Lee and Andy. July is about the right time frame . I will talk with Oneida.

I plan to use something like this on each end of the run although I may go with insulated boxes and pipe. The insulation should add some damping. It seems like I can effectively test the back pressure by opening and closing the machine room door and either listen, or measure air flow in the machine-side ductwork.

[Jim Becker]

The 10" equivalent is about what I used for my return, but mine isn't 25' long. For an air return, "bigger can be better" and as long as it's "bent", direct sound transmission will be mitigated. Here's how my return is constructed:

[mark mcfarlane]

Thanks Jim. I thought I'd get a similar baffle effect just by running through 10" flexible duct. I can zig-zag it and only travel 10 feet, and maybe put the output register in front of my overhead air cleaner. Two wall registers, 25 feet of duct. Will take about an hour to install before the drywall goes up.

Seems like an easier install than what you did, but probably more expensive, maybe $150 for mine. I plan to insulate the very short (3') shared wall with my shop, which precludes putting the return in the insulated wall.

[Jim Becker]

The exact "how" you do it matters less than making sure you have the volume available for flow and don't have a direct path for noise transmission. The flexible duct will do it!

[Vince Rosypal]

The Home theater guys over at AVSForum like the dead vent system that the soundproofing company talk about in this article
http://www.soundproofingcompany.com/...undproof-room/

[John K Jordan]

Depends on the volume and velocity of air you want blowing out of the return duct.

My 5 hp ClearVue cyclone sucks in air from a 6" duct, about 28 sq inches. I duct back into the room through a 144 sq in opening (with a filter and grate, just for fun), about five times the area of the input. There is no significant back pressure on the filters judging by the lack of force when opening a sealed door. All works well.

BTW, I built a plywood return duct snaked up through the trusses with angles and turns (stealth bomber stuff), sprayed the inside with rubber coating, and insulated outside with fiberglass batt. I wanted to minimize the sound coming through the duct and the ceiling. It worked.

This is my working sketch of the duct, grill for the return is in the ceiling, framing shown here before I put the ceiling up.

Dust_collector_baffle_small.jpg duct_ceiling_IMG_20141228_1.jpg

JKJ

[mark mcfarlane]

Thanks Jim, Vince and John.

I think I'll probably start with a simple flexible duct system and if I need more attenuation I can build something more substantial later. I don't need dead-quiet DC, just enough attenuation to make it more comfortable working in the shop.

I can't use the ceiling joist space, the joists run perpendicular to the direction I need to go, and will have R45 insulation blown in between the joists.

[Ole Anderson]

And those of you opting for a more, non-ducted route, line at least one side of the return with Safe-N-Sound mineral wool to minimize reflected sound.

[Kris Whitman]

IMG_7683.jpg

Here is a pic of my folded exhaust closet top. Obviously this was taken before I added the foamed 3/4" plywood top. My cyclone has a 7" inlet and exhaust which equates to 38.5 inches. I made my exhaust route 15"x15" or 225" which is just shy of 6 times as large as the cyclone exhaust. The lower right part of the picture is where the motor to the cyclone resides. By making the inlet to the folded exhaust originate by the motor my thinking was it forces all the air past the fins on the motor. I am just now closing up the closet so I do not know how effective it will be. The closet is standard stud construction with 5/8" sheetrock on the inside walls with Roxul insulation between studs then 5/8" sheetrock on the outside then another layer of OSB to match the shop walls. The door is a foam filled metal door with a good seal. I was tempted to buy green glue and add a second 5/8" plywood on the inside and outside but decided that a 15"x15" opening on top of the closet kind of made that idea pointless.

Time will tell if I wasted my time but I guess closing in the cyclone and not offering a direct path exhaust has got to improve the noise level. How much is the question. Time will tell. I'll let everyone know how it did once the closet is complete.

IMG_4804.jpg

Kris

[Jim Andrew]

Mark, if you really want to get your money's worth on blown insulation, just order the amount of insulation for the r factor you want and square footage from your local lumberyard, and have them bring out the blower at the same time. You will need one helper, someone to put the insulation in the hopper, and you just keep blowing till you get all the material in. I found that contractors tend to stop at a certain thickness, which is considerably less than what you paid for, as the stuff settles, and the manufacturer factors that in. Then call the yard and have them pick up the blower.