Thread: Do room filters work?

Originally Posted by Monty85

To get straight to the point. Do those small ceiling mounted room filters (such as this) work at all? Or are they just a waste of time?

I'm in a single car garage, with about 75% of the space dedicated to woodworking. Even with reasonable dust extraction, its difficult to contain everything and after a decent session i find the fine dust a bit noticeable and have to bail out of there for a while.

Would something small and reasonable cheap like these room filters do an ok job of filtering the air in a small area?

It depends what you are doing AND what you mean by "reasonable dust extraction".

If you only use unpowered hand tools room filers are adequate for everything except hand sanding.

If you use power tools and machinery, even in a small area, a reasonable dust extraction must;
- have the dust extractor vented or located outside the work area
- uses 6" ducting
- have the machinery ports opened up to accept the 6" ducting
- use a modified 2HP or better DC to utilise the 6" ducting

Anything less than this is simple "not reasonable" and will explain why the dust extraction is not working.

Using a room filters to try and clean up after "unreasonable" dust extraction is a bit of a waste of time.
It's a bit like operating a hospital without any sort of quarantining of patients (i.e. letting the sick patients wander all over the place) and hoping to collect the germs afterwards.

Room air filters are good for cleaning up an already clean area to get rid of ALL (not just wood) dust prior to applying finishes but they have no hope of keeping up with the dust escaping from "unreasonable dust extraction"

I would put your money into better/upgrading dust extraction first.

The air at work smells cleaner when they're running and I'm regularly cleaning the front corrugated filters, so they're clearly doing something...

If you wanted to try something reasonably cheap I think making something would be the way to go. I'd be going for a used truck air filter and a decent 240v blower fan or make a box and used a car radiator fan.

I used to throw out clean looking truck filters all the time at work.

Originally Posted by Ubernoob

If you wanted to try something reasonably cheap I think making something would be the way to go. I'd be going for a used truck air filter and a decent 240v blower fan or make a box and used a car radiator fan.

I used to throw out clean looking truck filters all the time at work.

Building a filter is not as easy as it sounds.

Most truck air filters are a bit coarse/inefficient for smaller wood dust particles.
Truck wear is greatest for dust particles in the 10-20 micron range which is why most truck filters concentrate on removing these dust sizes.
There are some truck filters that will filter much smaller particles so check the micron ratings.
A proper rating says not just the micron size but the efficiency at that size.
A decent breathable air filter should provide 99.9% efficiency at 0.3 microns.

Car radiator fans are typically axial fans and collapse and capitate under resistance so are not suitable for air filtration.
Only an impeller style fan can generate enough pressure to pull enough air through an air filter.

Originally Posted by BobL

Building a filter is not as easy as it sounds.

Most truck air filters are a bit coarse/inefficient for smaller wood dust particles.
Truck wear is greatest for dust particles in the 10-20 micron range which is why most truck filters concentrate on removing these dust sizes.
There are some truck filters that will filter much smaller particles so check the micron ratings.
A proper rating says not just the micron size but the efficiency at that size.
A decent breathable air filter should provide 99.9% efficiency at 0.3 microns.

Car radiator fans are typically axial fans and collapse and capitate under resistance so are not suitable for air filtration.
Only an impeller style fan can generate enough pressure to pull enough air through an air filter.

Well, there you go, I should do some research before handing out advice/ideas.
I think the two stage filters we used filtered 2-5 micron so as you say they wouldn't work as intended, I had no idea wood dust was so fine.

I might have to get a pressure gauge and see what sort of vacuum a radiator fan would pull, they use a similar fan on some AC condensers in a suck configuration and they would be quite restrictive I'd think.

Hi

Probably a question for BobL. Would a squirrel fan vented to the outside be another option to clean the air in a small workshop after reasonable dust extraction you describe above?

Originally Posted by BobL

It depends what you are doing AND what you mean by "reasonable dust extraction".

If you only use unpowered hand tools room filers are adequate for everything except hand sanding.

I have to disagree with BobL here.

If you only use unpowered hand tools you don't need a room air filter as you'll be producing chips and shavings that gravity will deposit on the floor.
Hand sanding will produce some dust, but most of it will stay within a few inches of where it is generated.

Originally Posted by MikeJ

Hi

Probably a question for BobL. Would a squirrel fan vented to the outside be another option to clean the air in a small workshop after reasonable dust extraction you describe above?

It depends on the capacity of the squirrel cage fan versus the clean air filter.

If these two fans have the same flow capacity a venting fan is a quicker option to get wood dust levels down because the dust is completely removed whereas a room air filter constantly recycles some of the dust.

However, over a longer time period, because a room filter does not draw in fresh air from the outside it will ultimately scrub a room cleaner of ALL dust than a venting fan but it will take longer to do it.

Here is a mock up of what I am referring to. RAF = Room air filter, VF is a venting fan.
Assuming they but have the same airflow rate and start at the same dust level of 1000 units.
Assumes air outside the shed has a natural dust level of 50 units

The vertical access is TOTAL dust.
So the RAF (Room air filter - Blue diamond) takes longer to clean up the room but eventually will keep cleaning the air and remove more dust - good for applying finishes.
The VF (Venting Fan - red squares) drops the dust levels more rapidly , BUT by after 4 units of time is drawing in as much air (containing natural dust) from the outside as it is removing.


RAFVVF.jpg

Assuming the external air is not a problem, the critical time for as much dust removal as possible is when there is the most dust in the air, which is immediately after the dust making activity ceases.
Ideally you want to drop the dust levels ASAP - this is why I recommend running a DC for 10-20-30 minutes after the last dust making activity.
However DCs make a lot of noise and chew a lot of power so that is why a lower powered quieter venting fan is a better option for this stage of the dust clean up process.

I have both types of fans i.e. VF and as super duper RAF - I rarely run my RAF BUT before I run it I stop making dust (i.e. go have lunch) and run the VF fan for 30 or so minutes. Then I run the RAF and within 15 minutes I have a shed with very clean air. This method also prevents the RAF getting clogged with too much dust - i.e. I have never had to clean my RAF in 4 years of use.

Thanks BobL. Looks like your approach is the way I need to go as well.

Thanks for the responses guys - and sorry for the delay in getting back.

Bob - I've considered the option of upgrading the dust extractor, but being such a small space its hard to workout how to fit a bigger unit in. I also find the main offender is fine dust being spat out of the top of my table saw and tackling that problem would mean upgrading to a better TS which I really can't justify the cost for.

But considering i'm not in their working very regularly (every other weekend if im lucky) the room filters seemed like something to consider being that I am out of the area for extended periods and although things look clean when I walk back in I imagine starting up a machine just blows all that fine dust up in to the air again.

So I guess what my hope with this thread was to determine if they actually make a positive difference or is it just money down the drain.

Originally Posted by Monty85

Thanks for the responses guys - and sorry for the delay in getting back.

Bob - I've considered the option of upgrading the dust extractor, but being such a small space its hard to workout how to fit a bigger unit in. I also find the main offender is fine dust being spat out of the top of my table saw and tackling that problem would mean upgrading to a better TS which I really can't justify the cost for.

Any dust you can see is not going to hurt you so chasing that is not really the best way to tackle the wood dust problem
Neither is upgrading the TS, even $10+k Table Saws have crap dust collection so thats not going to solve anything.

A much better performing over head guard can be made for under $100 from a sheet of perspex, but of course it assumes you have a decent DC to suck on it.

I made mine from a commercial dust picker arm, a small sheet of polycarbonate and some truck mudguard spray reducing bristles.

But considering i'm not in their working very regularly (every other weekend if im lucky) the room filters seemed like something to consider being that I am out of the area for extended periods and although things look clean when I walk back in I imagine starting up a machine just blows all that fine dust up in to the air again.

A room air filter cannot pick up any dust that settles out on the floor / machines surfaces. It has to grab that dust while the dust is suspended in the air and it will do that to a varying but most will settle out before its captured so it wont really solve the problem. It's much better to grab the dust at the source with a dust extractor.

You haven't said what dust extractor you are using and unless you vent or locate it outside nothing is really going to help.

Bob may not agree and he is the go to expert for this forum. what I did because of space was install a fan out of a aircon that you place on roof and have it drawing out any stray dust.I installed mine up as high as i could.

Originally Posted by DiRob

Bob may not agree and he is the go to expert for this forum. what I did because of space was install a fan out of a aircon that you place on roof and have it drawing out any stray dust.I installed mine up as high as i could.

I agree - this is a good move. Evaporative Aircons have excellent fans in them that can move very large amounts of air. What you have done by setting it up to extract rather than to blow air into a room is a better way to go. Fine dust rides upwards with the warm air generated by WW machines, removing it high up in the ceiling is more efficient than trying to blow it out of a window. After extraction at source this is one of the best things you can do.

one thing to consider with the room filters is how to clean them. I have used one for years ( in combination with a range of other dust extraction) and yes they collect dust that ultimately needs to be removed from the filters. can be a very messy job, where you are exposed to lots of fine dust. i take the internal filter bags outside and hose them down, in an attempt to contain the dust. eg: its much better to collect the dust at the source, if you can.