Dust FAQ

This is the dust fan from the old rec.woodworking discussion forum. Republished primarily for the discussions on ducting.

rec.woodworking – Dust FAQ v0.06  – 5/01/00
Written by Folklore (with much assistance)
copyright 1996-2000 Folklore

Redistribution, except through rec.woodworking newsgroup expressly prohibited.  May not be duplicated or published without written

Many thanks go to Gerry Glauser, Jim Thompson, John Lemmons, Bert Robbins, Brook (Dr. Vermin), Patrick Corrigan, CanoeCedar, Gary Hyde, Jeff Gorman, Alex Rodriquez, Daniel Shafner, DStig and several others for their informative and professional posts that provided the content for this FAQ.

I strongly recommend that you read the June 2000 issue of American Woodworker and the book ‘Woodshop Dust Control’ by Sandor Nagyszalanczy and that you visit http://www.airhand.com and http://www.oneida-air.com as well as http://www.jimthompson.net/family/dust%20collection.htm before making any major decisions.  These sources as well as others mentioned in and at the end of this FAQ have a wealth of good information and I did not feel it necessary to duplicate in this FAQ the valuable information already readily available.

Q.        Do you have any biases or legal issues in writing this?
Q.        Why should I include a dust collection system in my shop?
Q.        What types of systems are there?
Q.        Which one should I buy?
Q.        What are the CFM ratings I see on the systems?
Q.        What is FPM
Q.        What is Static Pressure or “Inches of Water” ?
Q.        How do I know what my CFM and SP requirements are?
Q.        What is ‘Face Velocity’?
Q.        How can the Oneida work without those attractive filter bags?
Q.         Should I put better bags on my big-bag system?
Q.        Should I replace the bottom filter with a trash can?
Q.        What size ducting do I need?
Q.        Is plastic pipe OK for ducting?
Q.        How about HVAC Ducting?
Q.        Is that nice looking clear 2″ dust collection pipe OK?
Q.         Where should I place my dust collection system?
Q.        How can I get to my Tablesaw in the middle of the floor?
Q.        Is it OK to exhaust outside?
Q.         Where can I find plans to build my own Cyclone?
Q.         If I build my own DC, Cyclone, or Air Filter, what type of fan do I need?
Q.        How can I connect a dust collector up to my contractors table saw?
Q.        How can I connect a dust collector up to my bandsaw?
Q.        How can I connect a dust collector up to my Mitre or Chop Saw?
Q.        The dust port on my xxxx is 2 ¼” or 2 ½”, where can I find fittings to connect this to my system?
Q.        What about dust from doing real fine work such as on a scroll saw?
Q.        How can I turn my DC on automatically when I open a blast gate?
Q.        Should I purchase or make one of the ceiling mount air-filtration systems like the JDS 2000?
Q.        What can I do about the filter on my wet/dry vac clogging?
Q.        What can I do with all of the shavings and sawdust once collected?
Q.        Once I have a dust collection system will I still need to wear a dust mask?
Q.        How can I keep from fogging up my safety glasses when I’m wearing a dust mask?
Q.        Is the dust from some woods more irritating than others?

Other Resources (There are many others, but these will get you started):
Q.         Do you have any biases or legal issues in writing this?

A.         This FAQ is intended as a brief overview of Dust Collection.  I
am not an expert in this field and have only spent enough time
researching this to come to my own conclusion about dust control.
Though the information in the FAQ is believed to be factual and
accurate, use at your own risk.  And now for the legal stuff:  This
article is provided as is without any express or implied warranties.
While every effort has been taken to ensure the accuracy of the
information contained in this article, the
author/maintainer/contributors assume(s) no responsibility for errors or
omissions or for damages resulting from the use of the information
contained herein.
Disclaimer: While I have tried to be objective in the writing of this
FAQ, I am human.  I started my search for dust collection thinking I
would buy a 650 CFM system, then quickly realized a 1200 CFM would be
more appropriate and made the purchase.  After more research I realized
that I would not be satisfied with the 1200, back it went, and I
currently have an Oneida on order.  There are many woodworkers who have
purchased 650, 1200, and 2000 CFM ‘big-bag’ dust collectors that have
been very satisfied with them and these systems have served their needs
very well.  As this FAQ points out you will need to make your own
determination regarding what is best for your situation.  Though I have
tried to be objective, my preferences may sneak in occasionally.  Please
forgive me when this happens.

Q.        Why should I include a dust collection system in my shop?

A.        There are 4 primary reasons for woodshop dust control.  These

Health concerns from dust particles – There have been numerous articles
written over the years about the health affects of breathing various
kinds of wood dust, which is now a known carcinogen.  I and many others
have worked in woodshops for years with no apparent ill affects (just as
many smoked for years with no apparent ill affects), however, the
mountain of evidence that breathing wood dust is harmful is growing.  Of
particular concern are particles of less than 5 microns and especially
those less than 1 micron.  It should be noted that adequate measures for
health may include a combination of dust collection, air filtration,
and/or dust masks.

Cleanliness – Cleaning up sawdust and shavings, especially from a
planer, can be a real pain and can reduce the enjoyment of the work we
are doing.   (This is a big plus for becoming a Neander.  Tom
Lie-Neilson will gladly provide us with a nice set of 3 planes for what
a power planer and dust collection will cost).  There’s really nothing
like stopping every 5 passes out of 60 through the planer to clear away
the shavings.  Further, dust control may reduce the maintenance on your
tools and extend their life. In some cases a good dust control system
can also save your marriage if you are getting complaints about the
beautiful coat of fine Jarrah on everything in the house.

Sometimes you just need it – For instance, on my router table there are
some operations that I could not perform at all without something to
handle the dust particles, otherwise I would have to stop numerous times
during even some single operations to wipe away the pile.  First option
was an air hose, an hour later option (it took me 55 minutes to go to
the store) was a fence-based collector connected to my wet/dry-vac.
Safety – This is a hotly debated topic, but there is a possibility of
any open flames or sparks creating an explosion, fireball, or fire from
the dust hanging in the air.  At this time this appears to be more
theory than reality as there are no known (at least to this group)
documented cases of these types of events in a small or home shop.  This
may be akin to saying that sugar is bad for you because when lab rats
were fed twice their weight in sugar on a daily basis for several years,
they died.  However, this is a serious problem in industrial
environments and may be a problem in some home environments so it is
included here for completeness and to encourage someone with
authoritative knowledge to step forward.

Q.        What types of systems are there?


  • Broom and Dust Pan (or for some, just a broom)
  • Wet/Dry Vac
  • Single-Stage Big Bag (currently the most popular, such as the Jet DC1200-1)
  • Two Stage portable (E.G., a canister with a bag on the side)
  • Two Stage (Separate chip collector and filter)
  • Integral Unit (Blower on top of Cyclone with some type of filtration such as Oneida)

This FAQ will concentrate on the last 3.  It is worth noting at this
point that a dust collection system such as the last 3 operate on
High-Volume, Low-Pressure vs. a wet/dry vac or household vac that
operates on High-Pressure (vac), Low-Volume.  There is a reason for

Q.        Which one should I buy?

A.        This depends on your shop and what you want to accomplish.  You
should ask yourself several questions before diving in:

  • Is health a concern?
  • Will I mind dragging a portable unit to each tool when I use them?
  • Do I want this for all tools or just my planer and jointer?
  • How often will I use the system?
  • Will the noise bother me?

For myself I have precious little time as it is to spend in my shop and
I want to insure that what time I am there is productive, enjoyable,
safe, and does not endanger my marriage.  Cleaning up debris piles,
moving a portable unit around all the time, annoyance of tripping over
flex duct on the floor, constantly having to empty bags, and a desire to
use this system on all power tools as well as cleanup from hand tools
led me to my decision that a central system was the only viable

Thus, my goals are:

  • Reduce health problems caused by dust.
  • Reduce amount of stuff tracked into house (Marriage Saver).
  • Automatically collect most of the dust and shavings from my tools so I can spend more time making sawdust and less time cleaning it up.
  • Easy to empty chip/dust collector
  • Quiet (I really don’t want the fine high-pitched whine of my planer disturbed by a loud dust collector)

Your goals may be different and will thus affect the system that you
build or purchase.

Q.        What are the CFM ratings I see on the systems?

A.        CFM stands for Cubic-Feet-per-Minute and is a measurement of the
volume of air transferred in a given amount of time.  For instance, a
home-shop planer generally requires 450 CFM of air movement to clear
away the dust, chips, and other debris.  Other stationary tools need
anywhere from 300 to 600.  Thus, at first blush you just need to
purchase a dust collector with a CFM rating higher than your tool with
the highest requirements.  Not So, CFM by itself is almost completely
useless.  You also need to understand a little about Static Pressure.
The CFM ratings on the boxes are often just the blower, these ratings
can be significantly less once filter bags and any flex or permanent
ducting are attached.

Q.        What is FPM
A.        FPM stands for Feet-Per-Minute and is a measurement of the velocity (speed) of the air.  It is related to CFM, but is different and important in it’s own right, especially if you are installing a dedicated duct system.  You want to insure that you maintain an airspeed of approximately 4000 FPM in branch circuits and a speed of 3500 in the main duct.  Too high a velocity (too small pipe) and your static pressure will go through the roof decreasing your CFM.  Too low velocity and you can have significant clogging.  The reason for this is that the dust collection system uses the air-flow to transport the wood chips and dust from your machine to the collector.  Too low a speed and the chips will no longer stay air-born resulting in chip settlement in ducts and a fair amount of time on your part un-clogging everything.  

For example, you need 400 CFM to clear the debris from your bandsaw.  A 4″ pipe at at 400 CFM will have a velocity of 3940 FPM.  This will work well. However, if instead you increase the pipe size to 6″ your air velocity will decrease to 2800 FPM.  At this rate some heavier particles can settle causing clogs.  This can be especially important in a branch with vertical runs where the correct air velocity is needed to lift the chips up the pipe.  A good example of changes in velocity with the same CFM is your outside water hose.  With the water turned on and nothing on the end you get a certain volume of water per minute, usually coming out pretty slow.  It wouldn’t do much to wash debris from your driveway. However, if you close down the end of the hose with your finger or with a nozzle, you will still get the same amount of volume per minute (CFM) as before, but the velocity or speed (FPM) at which it comes out is much greater and thus is able to do a good job of pushing debris from your drive.

The references at the end of this FAQ provide a more detailed description of this and how to calculate the FPM for your ducts.

Q.        What is Static Pressure or “Inches of Water” ?

A.        Static Pressure or SP is a measurement that is married to CFM. SP and CFM have an inverse relationship.  As SP increases CFM decreases. Some people refer to this as the suck power.  SP is a way of measuring and expressing the resistance of all of the components of a dust collection system. This resistance is caused by several things including bends in the hose or pipe that the air must move around, resistance from filter bags, etc.  Many dust collectors publish a CFM figure that is measured at 0″ of static pressure, sometimes referred to as free air flow or free fan flow (and likewise publish a SP number directly below that is at 0 CFM).  Measurements such as these are misleading.  These measurements are for a system with no resistance whatsoever (which is, BTW, impossible if you actually use the thing).  For instance, a collector might measure 1200 CFM without any pipe or filter bags connected.  As soon as you install the filter bags the CFM drops to about 1050 (for standard sized 30 micron bags, approximately 800 CFM for 5 micron and 600 CFM for 1 micron).  4″ flex hose has a static pressure of anywhere between 0.157″ to .210″ per linear foot.  Thus, if you add 10′ of flex hose between your dust collector and Planer you’ve added approximately 2″ of SP and again reduce your CFM.  Now you’re down to approximately 600 CFM at your tool (assuming 5 micron bags). .  An accurate measurement will be indicated as xx CFM @ xx” SP such as 560 CFM @ 7.62″ SP.

So, to know the performance of the dust collector you need to know what the CFM is at a given static pressure.  This is often referred to as the performance curve.  Following are some performance curve numbers for a typical single-stage, big-bag system.  These numbers are for just the blower and do not include filter bags or ducting.  (disclaimer: These measurements were produced quickly and are only psuedo scientific, but they do come very close to some numbers provided by the manufacturers*).

1.5hp / 1200 cfm
CFM        SP
1200        1.96
800        4.01
400        6.65
200        7.5
100        8.2
0        11

2hp / 1500 cfm
CFM        SP
1500        0.21
1200        2.22
800        4.2
400        7.63
200        8.79
100        9.33
0        11

3hp / 2000
CFM        SP
2000        3.91
1500        4.18
1200        6.72
800        8.45
400        10.11
200        10.89
100        11.43
0        12.57

Oneida 1.5hp integral cyclone/dust collector (per Oneida):
CFM        SP
1500        0.48″
750        8″

Though most manufacturers don’t openly publish their performance curve
information yet, all but one provided the information to me over the
phone once I got them to think I actually knew what I was talking about.
Since most people do not understand this information I can understand
their hesitancy in openly publishing these numbers since many people
might try to compare A’s 800 CFM @ 8″ SP with B’s 1200 CFM at 0″ SP and
incorrectly determine that B is better.  Ok, done with my defense of
manufacturers for the year.
It is also worth noting how much duct size will impact these
measurements.  All of the systems above will perform much better if only
a 6″ inlet is used (remove any double 4″ rigs that come with the

Q.        How do I know what my CFM and SP requirements are (remember, FPM should always be approximately 4000 in the branches and 3500 in the main duct)?

A.        This depends on several factors.  You need to start with your tool and determine what the CFM requirement for your tool is (it will not have a SP requirement).  Then add up all of the SP values from your tool to your dust collector.  Then add any correction factors for filters, etc.

Some typical tool requirements are:

  • TS                350 – 600 (faster ripping, or dado’s require higher CFM)
  • Bandsaw        400
  • Jointer                350
  • Planer                450
  • Mitre Saw        300
  • Router Table        350

Static Pressure values for 1′ straight spiral pipe at 4000 FPM are
generally (about 20% less for 3500 FPM):

  • 3″        0.10
  • 4″        0.07
  • 5″        0.055
  • 6″        0.045
  • 7″        0.038
  • 8″        0.030

Other duct elements are ratio’s of this:

  • 45 deg L                x4 – x7
  • 90 deg L                x8 – x15
  • Flex Duct        x2.5 – x3

Correction factors are:

  • 30 mic Filters        add 1″ SP
  • Cyclone                add 1-3″ SP
  • Dust Hood        add 1″ SP

Subtract 30% from effective CFM if using 5 micron instead of 30 micron filters and 50% if using 1 micron instead of 30 micron.

Example: a 90 degree elbow is the equivalent of 8 feet of pipe.  So 5’ of 4″ Flex Pipe, then a 90, then 20′ of 4″ spiral pipe = 10+8+20 = 38’ x .07 = 2.66″ SP

For a simple system, such as when you plan to drag a flex hose and/or collector to each tool individually, you can start with the tool with the highest requirement such as a Planer that requires 450 CFM.  Add 1” SP for the dust hood, 0.18″ per foot of flex ducting (say 12′), and 1” for filter bags.  This will give you a static pressure for the duct system of 4.16″ SP.  Thus you need a system that can deliver a minimum of 450 CFM @ 4.16″ SP.  The 1200 CFM unit above will meet this requirement (a 650 CFM unit may fall short).  But, if you decide to go with 5 micron bags (highly recommended) instead of 30 micron, you will reduce the available CFM by approximately 30%.  So on the 1200 CFM unit at 4.01″ SP (close to what we need) you will get 560 CFM, which should still be close enough (since 4.01″ SP is less than the 4.16″ we need then we will need a slightly higher CFM to compensate, but since we have 110 extra CFM delivered we should be OK).

If you get tired of emptying the bags and cleaning chips from the impeller (blower) you will probably add some type of chip separator. This will increase your SP by anywhere from 1″ to 3″ (depending on design) and may put you in a position of moving up to a 1500 or 1900 CFM unit.

If, on the other hand you decide to install permanent ducting, you will need to calculate your SP for the highest resistance run in your system.

My worst run is from my TS:

Feet        Dia ”        Desc                Factor        SP”
1                Hood                1        1
4        5        Flex Duct        0.165        0.66
6        5        Pipe                0.055        0.33
4        5        Flex                0.165        0.66
3        5        Pipe                0.055        0.165
9        5        90 deg                0.055        0.495
10        5        Vertical Rise        0.055        0.55
9        5        90 deg                0.055        0.495
28        6        Main                0.035        0.98
1        6        Flex                0.165        0.165
1                Cyclone                1        1
13        7        90 deg                0.026        0.338
13        7        90 deg                0.026        0.338
8        7        Vert                0.026        0.208
13        7        90 deg                0.026        0.338
1                Filter Loss        1        1
Total                                8.722″ SP

NOTE: in this calculation I calculated 5″ L’s at an equivalent of 9’ and 7″ L’s at an equivalent of 13′ which are the exact values for the Oneida pipe I am using.  Flex duct uses the exact SP value as provided by manufacturer.

Thus, I need 500 CFM @ 6.5″ SP at the cyclone entrance or 500 CFM @ 8.8” SP at the dust collector.  A 2hp/1500 unit would be close, but still fall under a bit, so I’d have to look at a 3hp/2000CFM unit if I go with this approach.

Oneida and Air-Handling systems (URL’s below) both provide some good information on designing systems and calculating SP”.  Make sure you order Air Handling Systems printed catalog.  Besides some good design information not included on their site, they have some very useful duct elements.

After all of my research, I’ve determined that the Oneida 1.5hp integral system is the best option for me.  No other combination of units can provide the same filtration from a health standpoint at anywhere near the $600 cost of the Oneida.  The Oneida takes up a 2′ x 2′ floor space that is significantly less than the 3′ x 5′ area a big-bag plus cyclone option will waste and will not require that everything be housed in a separate closet.  

It is possible to meet the second requirement of just chip collection (eg, we don’t care about our health) for less money, especially if we don’t mind building some stuff ourselves, emptying bags instead of cans,
and/or dragging flex duct to each tool each time we use them.  If you only use power tools occasionally, you can probably get by with a 1200 CFM DC, 5 micron bags, and maybe a garbage can cyclone (from Veritas) or homemade chip collector for less than $350.  Some people have also purchased 650CFM systems and been happy with the chip collection.  It will really come down to what you are trying to accomplish.


Q. What is ‘Face Velocity, why is it important, and how much filter area do I need?

A.        Face Velocity is the speed that air travels through the filter
medium and is a function of air offered to filter area.  Face Velocity
has a big impact on how well the filter medium works.  Too high a face
velocity and dust will get forced through the filters back into the air
you breath.  You want to maintain an air to filter area ratio of no
greater than 10:1 (10 cfm per square foot of filter).  This assumes that
you are using a good quality 16oz filter medium.  A ratio of 8:1 or 7:1
is much better.  Thus, if you have a 1200 cfm big-bag system with an
effective working cfm of 400 (after all static pressures are calculated)
then you will need at least 40 sq ft of filter material.  For a much
better explaination go to


Q.        How can the Oneida integrated cyclone/filter work without those attractive filter bags?

A.        The design of the filter cartridge on the Oneida provides for a
large surface area without large volume.  Keep in mind that with the
‘big bag’ type systems most of the bag volume is unused, especially if
you have a chip collector.  Since the 1st stage chip collector gets
everything but the really fine dust, all you really need is filter
surface area and enough air space to carry the air to the filter surface
and distribute it evenly.  For instance, on the big bag systems, you
could flatten the bags down to about 2″ – 4″ inside airspace and
everything would work as well (OK, almost as well, you need something to
distribute the air evenly across the surface area).  Also, the cyclone
on the Oneida is efficient enough to remove a large portion of the dust
prior to the filter, so what does make it to the filter already has a
fairly low dust content, thus extending the time between cleanings.

Q.        Should I put better bags on my big-bag system?

A.        Better can mean two things; A) Filters smaller particles and B)
More Surface Area.  

Most systems come with 30 micron bags.  If you place the system outside or in it’s own closet with better filters to filter the air returning to the shop then this might be OK, but most likely you will want a better filter.  Most mfr’s offer 5 micron and 1 micron bags and a few have 0.3 micron bags.  Some of these bags will significantly increase your SP, but some of the mfr’s have stated that they will not.  Comments from people who have used them range from no impact at all to “no suction left”.  Before you purchase ask the mfr to clearly outline to you what impact the new bags will have on SP compared with the stock bags. As we discovered above in our discussion on Face Velocity, you can almost always improve a system by increasing the surface area (larger bags).

Q.        Should I replace my lower bag with a chip collection can?

A.        The short and easy answer is absolutely not.  Doing this will
severely reduce the available filter area and thus increase the face
velocity of the remaining filter area.  The net result will be lower cfm
for your tools and a greater amount of harmful dust exhausted into the
air that you are breathing.  The more difficult answer is maybe.  As
long as you provide adequate filter area in the top bag for the air
volume you are moving (see face velocity above) this will make emptying
the chips much easier.  The problem will be getting an appropriate
amount of filter topside.  With even the smallest system you will need
at least 40 sq ft of 16oz felt fabric which is a 5′ high bag with a
diameter of 2.5′ (this is a very large bag).

Q.        What size ducting do I need? 

A.        This depends on your system, but generally for a single person shop you will have a 5″ or 6″ main duct with 4″ or 5″ branches.  It is important that you maintain approximately 4000 FPM in the branches and 3500 FPM in the mains.  The main duct is usually a straight horizontal run and thus a lower velocity will effectively convey the wood chips while a branch circuit usually has bends and vertical sections which need a higher velocity to insure that chips and other debris stay airborn.  Higher velocities also mean higher resistance and will have a negative impact on CFM thus your desire to use the lowest velocity possible that will insure all debris are carried to the cyclone or collector.

Oneida and Air Handling Systems (see URL’s at end) both provide good information on their sites for duct sizing and will design a ducting system for you if you order from them.

Q.        Is plastic or PVC pipe OK for ducting? 

A.        This has been a subject of much debate.  Personally I don’t
believe the cost of metal is enough over plastic to make it an issue for
me (depending on where you buy what).  All commercial shop systems
utilize spiral metal pipe.  Many people prefer plastic since it is less
expensive, easier to put together, and generally more available at local
stores.  However, plastic does require a ground wire either inside or
out to eliminate static electricity which lessens the ‘ease of install’
element.  If you do choose plastic, make sure that you get a large
enough inside diameter and that the wall thickness is appropriate for
the system you are installing.

Q.        How about HVAC Ducting? 

A.        HVAC ducting can work.  There are 2 critical elements to be
aware of though.  1) You need to make sure that you use wide elbows.
The elbow or WYE should have a radius of at least 1.5 times the diameter
of the pipe (EG, a 5″ elbow should have a radius of at least 7.5″)
Wider is better.  2) Use a minimum of 26 gauge metal and preferably 24
gauge.  Both are available from HVAC suppliers.  The lighter 28 and 30
gauge stuff sold at home stores can deform or crush when the system is
running.  (kinda fun to watch though if it’s someone else’s system).

Q.        My local store sells a nice looking line of tools including a dust collection system.  The dust system includes some cool looking 2” clear plastic pipe and has connectors for each of their tools.  Is this
a good choice?

A.        No.  This type of system is completely inadequate for stationary
woodworking tools.

Q.        Where should I place my dust collection system?

A.        Again, this depends, on several factors.  Preferably you want to
place the system in an enclosed dust room (actually a closet) with a
filtered air return to the shop.  This will lower dust in the shop air
as well as reduce the noise level.  You should never place a dust
collector near any type of open flame such as a furnace nor is it a good
idea to place the system near an entrance to your house.  If you like
science experiments, put a big bag type system with 1 micron filters in
your finishing room.
Also, if you buy a cyclone that you want to mount to a wall make sure
it’s not a wall with a room on the other side since air vibration will
cause a ‘buzz’.  Options are to build a stand for the cyclone, use
rubber isolation mounts between the cyclone and the brackets, or mount
isolation hangers in the ceiling with threaded rod used to hang the

Q.        How can I get to my Tablesaw in the middle of the floor?

A.        Many of us have tools in the middle of our shops and getting DC
duct to these can be a problem.  There are a couple of methods that
work.  The best option is to run the duct beneath the floor of your
shop.  This will completely eliminate having anything strung across the
floor or something coming down from the ceiling which could limit the
size of materials you work with on a tablesaw.  You can run this duct
beneath the floor (wood or concrete) in some shops or install a trench
with wood or metal grates over it.  Another option if you have a
concrete floor is to install a wood floor over the concrete.  This will
not only allow you to run electrical and dust collection to centralized
tools, but will also provide some comfort and longevity for your knees
and back and will look better.
A less desirable option is to drop the duct down from the ceiling.  This
can be tricky since you need the duct to come down directly next to your
TS to avoid having anything run across the floor.  Be careful that you
don’t limit your capacity too much.

Q.        Is it OK to exhaust outside?

A.        If you are in a temperate climate this might be a good option.
There are several things to keep in mind.  Exhausting the air outside
will cause negative pressure in your shop.  If this is within your
house, such as a basement, this could create a downdraft in your furnace
flue creating a very serious CO problem.  If you’re exhausting air you
need to make sure that the air can be easily replaced through some type
of vent.  If you’re not in a temperate climate you may need to consider
some type of air-to-air exchanger so that you don’t just exhaust hot
air, but instead xfer the heat to the fresh air coming in.  Also be
aware that the exhausted air may contain a fair amount of particulate
matter that could damage or ruin the looks of your house or garden
plants near the exhaust area.

Q.        Where can I find plans to build my own Cyclone?

A.        Wood Magazine ran an article in Dec ’98 covering this.  Penn
State has a package of the components here:
http://www.pennstateind.com/cyclon2.html.  Also check the Winter 1999
issue, # 120 of Wood magazine for an update to the design.
http://members.aol.com/woodmiser1/dust.htm has a unit that looks pretty
good as well.
Two critical things to keep in mind when building your own are to make
sure that you use a strong enough metal (24-20 gauge) to avoid collapse
from the negative air pressure and it is extremely important that the
dimensions are correct.  DrVermin posted the following a while back
concerning some basic dimensions:
A: The diameter of the top of the cyclone; i.e. the part that is not
B: The diameter of the pipe coming out of the top of the cyclone; i.e.
the outlet.
C: The diameter of the pipe coming in to the cyclone: i.e. the inlet.
D: The diameter of the opening at the bottom of the cyclone where the
chips and solids fall into a bin.
E: The vertical distance from the top of the outlet pipe to the top of
the untapered part of the cyclone.
F: The vertical height of the top (untapered part) of the cyclone.
G: The vertical height of the tapered part of the cyclone.
Actual               Dimensions (inches)
 CFM        HP     A       B        C       D      E      F      G
350-550     1      16       6        4        6      5      16     18.5
550-800     2      18       7        6        7      5      18     20.5
900-1200   3      21       8        7        8      5      21     24.5