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DC venting outside- exhaust run length

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Forum topic by neilp1 posted 12-01-2021 11:34 PM 417 views 0 times favorited 27 replies Add to Favorites Watch
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neilp1

14 posts in 46 days


12-01-2021 11:34 PM

Hi Guys

Moved back in march, to a new place with a 17×17 basement room with walkout, that im turning into my shop. Im drywalling over the next couple weeks, then getting my DC squared away

I have a HF 2HP unit ive been using for a couple years, plan to replace the impeller if Wen ever get more in stock. I have a 55 g blue barrel and an oneida Super DD, and plan to run 5” 26g metal duct, across the ceiling, with 3 drops. run length across ceiling is 15 feet. ususal designm priniples apply- ill be adding 5” hole plywood hangers for extra reinforcement

Anyway- the layout of the room means i can put the DC in its own closet by the door, and have the motor up in the ceiling rafter space, and have the suction line run real close to the tools. this frees up a 5’ wide bay next to the exterior wall where i can keep my large format CNC. This would put the exhaust side 12 feet away from the external wall, and i plan to port outside, using 6” flex duct (exhaust port on DC is 5”) for noise abatement (Penz site and some australian forums recommend this).

However- i never see discussions on how the exhaust length affects things, and i wont be in a position to do a real test until its all installed. Any thoughts on what impact a 12’ run of oversized exhaust duct will have?

thanks


27 replies so far

View Robert's profile

Robert

4827 posts in 2811 days


#1 posted 12-03-2021 02:09 PM

I would straight pipe it not use flex.

You’ve considered air loss? I assume since it’s a basement you’re in climate with cold winters.

-- Everything is a prototype thats why its one of a kind!!

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neilp1

14 posts in 46 days


#2 posted 12-03-2021 02:25 PM



I would straight pipe it not use flex.

You’ve considered air loss? I assume since it’s a basement you’re in climate with cold winters.

- Robert

Thanks for the reply.

I planned on flex because I’ve seen it mentioned in Pentz site that increasing the pipe size and going to insulated flex would help with noise abatement. I’m not married to the idea and can certainly do straight pipe as a change if I suspect it is impacting flow

Basement is unconditioned, so not concerned with losing conditioned air, but I do plan on a vent across the room from DC for make up air- 100 square inches, unrestricted vs the 6” diameter exhaust with 30 square inches (rounded up) . The closet will also be baffle vented

View Albert's profile

Albert

557 posts in 4920 days


#3 posted 12-03-2021 03:12 PM

I have my Delta 1 1/2 HP plumbed with 4 inch plastic tube, the DC is outside the shop and it runs inside to all the tool branches, also outside I have Teed into it with another gate to shut off the outside when not in use, the outside T is for a sawmill collectior that I’ve used for several years now. The exhaust dust blows another 40 feet so everything ends up in some woods that are nearby. I doubt you’ll have a problem.
Anyhow, it works great and the dust comes blasting out with plenty of pressure and has never caused a problem. Most noise is eliminated, no neighbors nearby. Hope this helps.

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neilp1

14 posts in 46 days


#4 posted 12-03-2021 03:18 PM



I have my Delta 1 1/2 HP plumbed with 4 inch plastic tube, the DC is outside the shop and it runs inside to all the tool branches, also outside I have Teed into it with another gate to shut off the outside when not in use, the outside T is for a sawmill collection that I ve used for several years now. The exhaust dust blows another 40 feet so everything ends up in some woods that are nearby. I doubt you ll have a problem.
Anyhow, it works great and the dust comes blasting out with plenty of pressure and has never caused a problem. Most noise is eliminated, no neighbors nearby. Hope this helps.

- Albert

Great- sounds like I shouldn’t have much of an issue as long as I keep the rest of the system as optimized as possible.

Thanks!

Got any pics?

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clagwell

400 posts in 1123 days


#5 posted 12-03-2021 06:35 PM

The effect of duct and fittings is very nearly the same for the outlet as it is for the inlet side. If it’s not a dead straight run you might want to consider 8” flex, especially if it’s the insulated HVAC type.

Also, it will help to eliminate the 5” transition on the blower outlet. Make an adapter that lets you connect straight to the hose. That transition has a flow resistance equivalent to about sixteen feet of 5” metal duct.

-- Dave, Tippecanoe County, IN --- Is there a corollary to Beranek.s Law that applies to dust collection?

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neilp1

14 posts in 46 days


#6 posted 12-03-2021 07:14 PM



The effect of duct and fittings is very nearly the same for the outlet as it is for the inlet side. If it s not a dead straight run you might want to consider 8” flex, especially if it s the insulated HVAC type.

Also, it will help to eliminate the 5” transition on the blower outlet. Make an adapter that lets you connect straight to the hose. That transition has a flow resistance equivalent to about sixteen feet of 5” metal duct.

- clagwell

thanks

I wouldn’t have intrinsically thought that would be the case. good to know.

it is a straight run, and it terminates in a 6” wall cap. i hadn’t considered going much bigger than that, since i didn’t want to go too much bigger than the outlet, for velocity reasons. didn’t want what little amount of dust that got out to deposit in the vent. plus ive already bought the flex and just installed the cap

the transition- are you talking about the black plastic piece that takes it from rectangular to 5” circle? that eats 15’? Ouch. I have a 5-6” adapter on there now, but i may try to figure out how to use a 6” take off and a piece of board to make a better transition, and bypass the 5”. any idea how id actually do it?

thanks

View Madmark2's profile

Madmark2

3247 posts in 1919 days


#7 posted 12-03-2021 07:20 PM

What type of heating do you have? You don’t want to be pulling CO (carbon monoxide) into your home by reversing the furnace’s draft. If you’re pumping out 1000+ cfm of air, the makeup will draw from wherever it can. You’re not going to have the walkout open 100% of the time and, when closed, the air will be drawn from the house.

-- The hump with the stump and the pump!

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fivecodys

1767 posts in 2967 days


#8 posted 12-03-2021 07:23 PM


I planned on flex because I’ve seen it mentioned in Pentz site that increasing the pipe size and going to insulated flex would help with noise abatement. I’m not married to the idea and can certainly do straight pipe as a change if I suspect it is impacting flow

- neilp1

It absolutely reduces noise levels. I vent directly outside (post Super Dust Deputy) and I originally used straight pipe and it was very loud. I was quite surprised really. I read the same article you have and I went to insulated flex pipe and it reduced the noise level significantly. The wife noticed the difference right away. I use a 6” dryer vent through the wall of the garage. She was the one who noticed how loud it was.

Here is the original set up:

Here it is after I changed over to the insulated flex pipe:

My vent dumps into the front yard flower bed:

I’m using 6” Insulated ducting.

Make SURE you have no source of combustion in your basement like a furnace or a gas water heater. You may inadvertently pull exhaust gases into your shop as the DC tried to replace the air that it is venting outdoors. That my friend is very dangerous!!

I hope this is helpful.

-- A bad day woodworking is still better than a good day working.

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neilp1

14 posts in 46 days


#9 posted 12-03-2021 07:33 PM

I planned on flex because I’ve seen it mentioned in Pentz site that increasing the pipe size and going to insulated flex would help with noise abatement. I’m not married to the idea and can certainly do straight pipe as a change if I suspect it is impacting flow

- neilp1

It absolutely reduces noise levels. I vent directly outside (post Super Dust Deputy) and I originally used straight pipe and it was very loud. I was quite surprised really. I read the same article you have and I went to insulated flex pipe and it reduced the noise level significantly. The wife noticed the difference right away. I use a 6” dryer vent through the wall of the garage. She was the one who noticed how loud it was.

Here is the original set up:

Here it is after I changed over to the insulated flex pipe:

My vent dumps into the front yard flower bed:

I m using 6” Insulated ducting.

Make SURE you have no source of combustion in your basement like a furnace or a gas water heater. You may inadvertently pull exhaust gases into your shop as the DC tried to replace the air that it is venting outdoors. That my friend is very dangerous!!

I hope this is helpful.

- fivecodys

i believe a comment of yours earlier in the year is what clued me into the insulated duct.

you seem to be running about 8 feet of duct, plus the bends- i think thatll about match us out in terms of calculations. glad to hear i am on the right path (for a system that doesnt underperform too badly)

thanks!

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neilp1

14 posts in 46 days


#10 posted 12-03-2021 07:39 PM


If you re pumping out 1000+ cfm of air, the makeup will draw from wherever it can. You re not going to have the walkout open 100% of the time and, when closed, the air will be drawn from the house.

- Madmark2

Make SURE you have no source of combustion in your basement like a furnace or a gas water heater. You may inadvertently pull exhaust gases into your shop as the DC tried to replace the air that it is venting outdoors. That my friend is very dangerous!!

I hope this is helpful.

- fivecodys

I have a way oversized (100sqIn) vent intake that im putting in the wall across the room, for my make-up air. shop door will be closed, and itll be practically hermetically sealed by the time the drywall is taped, mudded and painted. ceiling too. also a hallway door and the furnace room door will be closed too. so hopefully 100% of my makeup will be coming through the wall intake

I also do pretty extensive marine aquariums, and have a ‘fishroom’ in my basement that pumps out 600cfm of 85% humidity air when things get warm in summer. i learned very quickly early on that a proper make-up air system is essential. no matter how leaky the house is.

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bigblockyeti

7949 posts in 3051 days


#11 posted 12-03-2021 08:00 PM

At only 100 square inches, that’s still going to have pretty high air velocity through that intake vent and likely substantial negative pressure too. I would frame it out larger and run some tests to see what kind of vacuum pressure you’re actually seeing, too much can actually rip the drywall from the floor joists above.

-- "Lack of effort will result in failure with amazing predictability" - Me

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neilp1

14 posts in 46 days


#12 posted 12-03-2021 08:06 PM


At only 100 square inches, that s still going to have pretty high air velocity through that intake vent and likely substantial negative pressure too. I would frame it out larger and run some tests to see what kind of vacuum pressure you re actually seeing, too much can actually rip the drywall from the floor joists above.

- bigblockyeti

That’s 100sqin intake (10×10) for an exhaust that’s 30sqin. I thought 3.5x area would be more than enough. But I guess I can try to find a bigger one.

Not sure I understand about ripping the drywall off the joist. The negative pressure from a 1.5hp HF sucking my ceiling off?

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clagwell

400 posts in 1123 days


#13 posted 12-03-2021 08:39 PM


The effect of duct and fittings is very nearly the same for the outlet as it is for the inlet side.
I wouldn t have intrinsically thought that would be the case. good to know.
Inlet and outlet are only relative to the location of the observer. If you’re inside a cyclone then to you the outlet is what, from the outside, looks like the inlet. If you’re outside the building when ventong outside then your make up air opening looks like an inlet while from the inside of the building it’s an outlet.
It’s all just a closed path from as far as the fan can tell.
i hadn t considered going much bigger than that, since i didn t want to go too much bigger than the outlet, for velocity reasons. didn t want what little amount of dust that got out to deposit in the vent.
If the fine dust could really drop out of suspension that quickly you wouldn’t need to be concerned with it in your environment because there wouldn’t be any floating around.
plus ive already bought the flex and just installed the cap
That makes it all moot.;)

the transition- are you talking about the black plastic piece that takes it from rectangular to 5” circle? that eats 15 ? Ouch. I have a 5-6” adapter on there now, but i may try to figure out how to use a 6” take off and a piece of board to make a better transition, and bypass the 5”. any idea how id actually do it?
Yes, that black plastic outlet transition. You can see the difference it makes in the fan curve, it’s the difference the curves marked 1 and 2:
As far as fabricating a transition, if you have a 3D printer that’s the obvious choice. But you probably don’t have one or you would already know that. A 4×8x6 straight register boot could be hacked into a decent fitting if you don’t mind messing with sheet metal. The Aussie forum you mentioned has at least one example of someone forming 6” PVC sewer & drain pipe into a nice looking transition.

-- Dave, Tippecanoe County, IN --- Is there a corollary to Beranek.s Law that applies to dust collection?

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clagwell

400 posts in 1123 days


#14 posted 12-03-2021 08:49 PM



At only 100 square inches, that s still going to have pretty high air velocity through that intake vent and likely substantial negative pressure too. I would frame it out larger and run some tests to see what kind of vacuum pressure you re actually seeing, too much can actually rip the drywall from the floor joists above.

- bigblockyeti


500 CFM through 100 square inches is 720 feet per minute. That’s a velocity pressure of 0.032 inch water gauge. That’s 0.17 pound per square foot. Maybe as much as double that with 100% entrance loss. A total of 14 pounds on a 4×10 sheet of drywall.

-- Dave, Tippecanoe County, IN --- Is there a corollary to Beranek.s Law that applies to dust collection?

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neilp1

14 posts in 46 days


#15 posted 12-03-2021 09:43 PM

At only 100 square inches, that s still going to have pretty high air velocity through that intake vent and likely substantial negative pressure too. I would frame it out larger and run some tests to see what kind of vacuum pressure you re actually seeing, too much can actually rip the drywall from the floor joists above.

- bigblockyeti

500 CFM through 100 square inches is 720 feet per minute. That s a velocity pressure of 0.032 inch water gauge. That s 0.17 pound per square foot. Maybe as much as double that with 100% entrance loss. A total of 14 pounds on a 4×10 sheet of drywall.

- clagwell

appreciate the math. im a Bio-nerd, so fluid dynamics and air velocity etc is new to me. So- is 14 lbs on a sheet past failure point of the tape, mud and screws?

with the intake velocity – my bio-nerd guess would have put it at 20% the achievable velocity at the end of the 5” diameter hose, since 100sqin/ 19.6 sqIn, so around 200cfm. 700 fpm is crazy. Do people just not appreciate this given leaky garage doors etc? what about people with sealed shops- slamming doors and whistling noises, or does everyone do 400 sqin/ multiple intakes?

thanks for adding to my list of stuff i need to stress about, lol

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