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Dust Collection: Ducts in the Attic?

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Forum topic by tomconlin posted 04-19-2021 10:18 AM 390 views 0 times favorited 14 replies Add to Favorites Watch
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tomconlin

4 posts in 2299 days


04-19-2021 10:18 AM

Topic tags/keywords: dust collection dust collector attic duct

Hey there everyone. I’m getting started putting in permanent dust collection in my 20×30 shop. I am looking at putting a dust collector in the boiler/water heater room (It will have a return air vent to the shop). . I’m looking at running metal or PVC ducts (6” hopefully) up into the attic, dropping it down through the 9 foot high ceiling along the way. I’m in central Ohio, where we get up to 90° in the summer and well below freezing in the winter. The dust collector would be in the heated shop. The ducts would be in the hot/cold attic. Any issues with CFM, temperature, and airflow? So the big question is, any difference between hanging duct below the ceiling in the shop or laying it above the ceiling in the attic?


14 replies so far

View Fred Hargis's profile

Fred Hargis

6986 posts in 3575 days


#1 posted 04-19-2021 10:40 AM

I’m not sure of the answer, but that won’t keep me from speculating. One thing I wouldn’t like about it is the ceiling penetrations you’ll have to make…but you didn’t ask about those. So, for the other stuff….depending on the DC itself, I don’t see your CFM being different…at least not in a way that could be measured, that would also be airflow. I suppose the ducting could act as a heat exchanger, heating the air in the summer and cooling it in the winter, and my guess is it would be worse in the summer. My DC seems to kick out the air warmer than it was anyway, you would just be compounding (maybe) that problem. That warming the DC does isn’t trivial, at least on mine. I can feel the shop warm up if I run it for an extended time. The one thing I’m wondering about the most is the possibility of condensation on the ductwork, that alone might keep me from putting it in the attic. We here in Ohio get some really humid days once in a while and it could be a real problem. I will add, I had a chop with 9’ ceilings and 6” ductwork didn’t seem to be a problem with that…your life will be a lot simpler if it’s inside the shop. Besides you may need (will need) to reconfigure it someday; or even clear a clog.

-- Our village hasn't lost it's idiot, he was elected to congress.

View tvrgeek's profile

tvrgeek

1865 posts in 2730 days


#2 posted 04-19-2021 10:45 AM

I would insulate the duct just to reduce possible condensation, but I see no problem if PVC.

View ibewjon's profile

ibewjon

2413 posts in 3874 days


#3 posted 04-19-2021 01:19 PM

No way would I put a dc in a room with a boiler and water heater. I think the fine dust escaping from the filter could cause problems with the other units, and even be a fire hazzard.

View RClark's profile

RClark

126 posts in 3266 days


#4 posted 04-19-2021 03:03 PM

I don’t know about the cold/hot aspect, but two other aspects should be considered:

- Are you adding (potentially unnecessary) run length to the system? I don’t know the specifics of your configuration, of course, and you might be able to make it “length neutral.” But you also might make it longer by having to work around building structure in the attic.

- How accessible will your “in attic” runs be in the event you need to clear an obstruction?

-- Ray

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splintergroup

5122 posts in 2304 days


#5 posted 04-19-2021 04:35 PM

Main issue I see is the higher “lift” height for heavy (planer) shavings, maybe an additional foot.
The idea of no horizontal duct runs obstruction the ceiling is appealing.
Reconfiguration would be more of a challenge.

View tomconlin's profile

tomconlin

4 posts in 2299 days


#6 posted 04-19-2021 04:46 PM

ibewjon, good point. Gas boiler, so dust and pilot light problems I hadn’t even considered. Thanks. I look at moving the DC into the adjoining small room that I was going to use as a finishing spray room. I can isolate the DC in that area, and would not be running it while I’m spraying finish in there. RClark, there isn’t much difference at all in my planned duct run routing between running it above or below the ceiling, fortunately. It’s six of one, half a dozen of the other. I think obstructions are gonna be a pain whether I’m going up a ladder into the attic or up on a ladder reaching for the ceiling. Too bad there isn’t any inexpensive clear pvc pipe out there.
As far as condensation goes, that’s my big unknown. My guess – unproven – is that condensation will probably form after the DC is shut off. Moving air will probably not allow a lot of condensation to occur, even when running for a long time. But after warm air has stopped moving through a cold attic pipe, I could see some condensation forming in the pipe. My guess only. And it’s also possible that that condensation could go away before the next use of the dust collector, although when I’m in the shop the the DC is turned on and off quite a bit. I really don’t know the answer to that one. Insulating the ducts might be a pretty good thing to do. Can’t hurt.

View Kelly's profile

Kelly

3548 posts in 4025 days


#7 posted 04-19-2021 07:14 PM

ibewjon brings up a very good point on potential danger, whether it’s because you put dust in a flame zone or because you created a negative pressure in the boiler room, bringing CO2 in.

I agree with tvrgeek’s response on the heat exchange issue (I suspect you already knew the answer).

I’ve contemplated moving my four bag beasts up into the attic. However, that would mean building a box to house the collector, so conditioned air could be returned through the ceiling back to the shop.

Too, the summers get up to 120 here, so the attic can be the temperature of the sun, and twenty below in the winter, so such an approach would require insulating the box well, to avoid losing heated or cooled air.

The upside would be, I’d gain a lot of room back and would only have to deal with a cyclone down in the shop. Add the fact I have three collectors, that’s a lot of new toy room.

View Madmark2's profile

Madmark2

2651 posts in 1669 days


#8 posted 04-19-2021 07:58 PM

Attic ducts should be fun to find/clear a clog. Clogs like to form on surfaces that have condensation.

If you’ve got the static pressure to spare an extra 2’ of lift for everything shouldn’t be much additional load.

Long runs with blast gates at each tool waste your static pressure. A manifold at the DC separator with straight runs to each tool is better. This also implies a central location for the collector.

Perimeter piping plans are least efficient. Central location eliminates your longest runs effectively cutting the static pressure loss in half, albeit slightly increasing the losses at the nearer ports. Centralized suction is more evenly distributed.

Plan for dual 45° elbows instead of a single 90°. No hard T’s. If you must use Y’s use curved ones with the base towards the DC.

The volume of hot or cold air in the ductwork should be less than 100 cu ft. No matter how hot or cold the air is, the volume is small relative to the shop. You might feel a momentary blast of warm or cool since an 1100 cfm blower will completely change the air in the ducts in five or six seconds.

-- The hump with the stump and the pump!

View Mosquito's profile

Mosquito

11106 posts in 3374 days


#9 posted 04-19-2021 08:32 PM


Moving air will probably not allow a lot of condensation to occur, even when running for a long time.
- tomconlin

By that, you probably mean accumulate, as it will definitely form. Look at how a dehumidifier works.

Condensation would probably be my main concern in both seasons where I am (MN), as the warm air with cold attic condensing inside the pipe in thew inter, and cooler shop air with a hot muggy attic in the summer condensing on the outside. I’d say definitely insulate the duct up there if you can. I’d treat it no different than a standard HVAC run in an attic space. If nothing else, I wouldn’t want a large convection exchange to my attic in any seasons, whether it’s drawing warm in from the attic in the summer, or cold in during the winter. But, if you’re not concerned about the heating or cooling being impacted by it, I’d much rather have my runs in the attic than hanging from the ceiling if I could, if it works out

-- Mos - Twin Cities, MN - http://www.youtube.com/MosquitoMods - http://www.TheModsquito.com

View tomconlin's profile

tomconlin

4 posts in 2299 days


#10 posted 04-19-2021 10:12 PM

Yep, condensate inside the ducts is bad stuff, not too worried about the heat exchange otherwise. 20×30 space, 6‘ x 12‘ mechanical room with the gas boiler, 12×12 adjoining room which was to be my spray booth area. I could put the DC in a quarter, and close it with a return air vent of adequate size, in order to cut down all the noise in the shop. The reason I want ductwork in the attic is because I have lots of long boards and I am as graceful as a one legged elephant. I’m sure I would be bashing ducts all day long if they were hung from the ceiling. Basically, if I put the DC in either of the rooms off to the south side, it won’t be centralized, but I will probably have three different runs branching out from where the 6 inch duct enters the attic. It will split off towards the west, east, and north walls from the south end of the shop. Right now my plan is to have ceiling drops in three locations in the shop, with manifolds at each of the three drops. These manifolds with the accompanying blast gates would control the tools in three zones and hopefully minimize pressure loss.
Right now I’m guessing that my system should be about 1500 CFM, 3 hp, 220 V single phase.

View ibewjon's profile

ibewjon

2413 posts in 3874 days


#11 posted 04-19-2021 10:38 PM

There is an insulating sock that just pulls over the duct, but that makes finding / clearing alot harder. My duct is exposed, but I put in a couple y fittings that are capped to use as future cleanouts if needed. My ducts are along the wall, making for shorter runs in my shop. Splitting into zones is a good idea. I split my duct into two zones, and one of those will be split into two zones when I extend my future duct plans.

View Kelly's profile

Kelly

3548 posts in 4025 days


#12 posted 04-20-2021 03:34 AM

I can verify this via first hand knowledge. Initially, I had gates for each item. Even if they sealed well, adding a few made a notable change without any equipment.

It dawned on me, it took as long to walk to one piece of equipment to close the gate, then go to the one I was going to use and open a gate as it did to do both swaps at the cyclone. As such, I have short runs to the equipment (center location, as you say) and just swap hoses, instead of playing with gates. Eye hooks on the ceiling support ropes that hold two hoses (one on each end) at the input level of the cyclone.

Doing away with Y’s and elbows made a notable improvement in collection power.

Of course, this approach isn’t ideal for all.


[L]ong runs with blast gates at each tool waste your static pressure. A manifold at the DC separator with straight runs to each tool is better. This also implies a central location for the collector.

.. . .
- Madmark2


View WoodES's profile

WoodES

191 posts in 2772 days


#13 posted 04-20-2021 03:35 AM



Main issue I see is the higher “lift” height for heavy (planer) shavings, maybe an additional foot.
The idea of no horizontal duct runs obstruction the ceiling is appealing.
Reconfiguration would be more of a challenge.

- splintergroup

One solution to the larger chip collection is add a trash can separator close to the source. Larger chips fall out out there and the fine dust goes to the final collection point. I had the same problem with my system and added this stage for the table saw & jointer (they share the same run). Solved the issue until I installed a cartridge filter in the system. The DC really sucks now….

I put my 6”pvc runs in in the rafters, and when I need to clean it out I crank up the leaf blower on each drop until the separator clears.

View tomconlin's profile

tomconlin

4 posts in 2299 days


#14 posted 04-21-2021 01:41 AM

Kelly – Swapping hose vs blast gates is definitely food for thought. I’ve got a lathe near my CNC in a corner, I could easily set up ala drop from the ceiling with one hose to swap between them (more efficient), or set up a manifold about 3 feet below the ceiling and have a gate for the CNC and another for the lathe (less efficient, more convenient). I got a cheapo anemometer from Amazon so I can test how bad the pressure drop is either way, but your way probably wins.
WoodES – I like the trash can separator idea, and already have one between my CNC and a roughly 25 yr old Delta collector I was given. It does pick up a lot of wood prior to the filter bags, no reason it shouldn’t work in the new system. Also, I LOVE the leaf blower idea. I use mine for lots of jobs, including blasting out the dryer lint from inside the house out to the exhaust vent under a low deck. Saves me crawling around under there. I’m sure it would handle most duct clogs just fine.

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