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What size and capacity extraction fan for a spray booth?

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Forum topic by stefang posted 11-13-2014 06:42 PM 1883 views 0 times favorited 27 replies Add to Favorites Watch
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stefang

15512 posts in 2801 days


11-13-2014 06:42 PM

I will be building a spray booth for my new Earlex 5500. I plan to only spray waterborne finishes onto small to medium sized projects. I would like opinions on what would be an appropriate size/capacity fan. I know many go by the bigger the better philosophy and I can understand that, but I would really like to know what would work starting at the lower end and up to max needed. I will appreciate any help I can get.

-- Mike, an American living in Norway.


27 replies so far

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patron

13538 posts in 2808 days


#1 posted 11-13-2014 07:06 PM

one off the problems with extractor fans
aside from explosive finishes
is the finish clings to the blades

i did read a post here
about having a fan before the booth
and let the over pressure force the air out
without clinging to the blades
or being in the stream if you do use volatile finishes
anything that moves the air past the in filter
(you do want clean filtered air )
and out past the exit filter should work just fine
(i have a special fan that is spark free in mine
but it cost $400 when i got t)

i also read that water mist before spraying in the booth
will act as a magnet for any airborne particles of dust
plan to do that in my booth
when i get it up and running
and do have good lighting
so you can see the finish right
from all angles

-- david - only thru kindness can this world be whole . If we don't succeed we run the risk of failure. Dan Quayle

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bigblockyeti

3668 posts in 1187 days


#2 posted 11-13-2014 07:18 PM

I have a few old cast aluminum spray booth fans made by Dayton and they were rated for a maximum of 3500rpm, despite their small diameter, they should provide substantial air flow. With these, you’d have to have an explosion proof motor to keep from potentially igniting the aerosol overspray, provided you were spraying a combustible finish. I’ve seen three phase motors used with a remote VFD to offer adjustability to the airflow based on the requirement of the job.

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stefang

15512 posts in 2801 days


#3 posted 11-13-2014 07:42 PM

Thanks David and BBY. I won’t be spraying oil based finishes so I won’t need an explosion proof fan. The RPM rating doesn’t tell me much. It’s easier to relate to the CFM rating which give some idea about it’s actual capacity. I am thinking max would be 6000cfm, but those are pretty expensive here (about $330), so I’m hoping a lower rating (and thereby cheaper) will still work, aided by a fan providing filtered input air. I know you can get pretty cheap box fans at the big box stores in the States, but not here. I am trying to find one in the U.K. at a more reasonable price, but without much luck so far. I did find an 18” 3 speed fan for about $150 which is rated at 2200cfm, but I don’t know if that will do the job.

-- Mike, an American living in Norway.

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TopamaxSurvivor

17676 posts in 3143 days


#4 posted 11-14-2014 03:34 AM

These are really common in the US. Not sure how you would go about getting one to Norway and it will be 120 volt. Putting 2 in series would be cheaper than a transformer to drop the volts and double the air flow.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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stefang

15512 posts in 2801 days


#5 posted 11-14-2014 09:08 AM

Ridiculously low priced compared to here. You do have a good idea there though Bob. Maybe I should think about using 2 smaller fans. I hadn’t thought of of that.

-- Mike, an American living in Norway.

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canadianchips

2360 posts in 2464 days


#6 posted 11-14-2014 02:44 PM

We used these in our welding school at the oxy.ace. cutting table.
Downside in welding, the filter plugged to fast. Paint particles might be similar.
It was portable.
It had squirrel cage fans inside.
More cfm at lower rpm.

-- "My mission in life - make everyone smile !"

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GregD

783 posts in 2603 days


#7 posted 11-14-2014 03:22 PM

I have only a small amount of relevant experience but I think a simple box fan or two like Topamax suggested would be enough to keep up with the overspray mist for typical woodworking projects. I don’t get so much airborne mist using my Earlex 6900 unless I’m spraying a latex type paint. By contrast I get a lot of overspray from heavy bodied paint (latex, etc.), using an airless sprayer, and/or spraying large surfaces that wouldn’t fit in a spray booth (interior walls/ceilings).

When I do occasionally set up a booth it is in a utilitarian garage where loosing a bit of overspray from the booth won’t be noticeable, so I use simple and inexpensive setups. If I were regularly spraying finish and my spray booth was in a nice, clean workspace, I might put more effort into more complete capture of overspray.

-- Greg D.

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stefang

15512 posts in 2801 days


#8 posted 11-14-2014 04:33 PM

Thanks CC and Greg. I did find an article this afternoon by Jeff Jewitt in Fine woodworking com where he had shows how to make a simple homemade spray booth. He said a fan rated at 2000 CFM should be sufficient and he suggested using at least a 16” diameter fan. That sounds pretty good to me. I checked Ebay and others in the U.K. and they have inexpensive 20” box fans, but none show the CFM rating. I guess I will just have to keep looking.

-- Mike, an American living in Norway.

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TopamaxSurvivor

17676 posts in 3143 days


#9 posted 11-14-2014 09:50 PM

Mike, I was suggesting 2 in series to use 220 volts you have, but 2 small fans should more more air. The inexpensive 20” box fans you found probably move enough air. The one I linked moves 2200 cfm. Most fans that size should be fairly close even with the 50 vs 60 hz difference.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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stefang

15512 posts in 2801 days


#10 posted 11-14-2014 09:55 PM

Thanks Bob, I will keep that in mind.

-- Mike, an American living in Norway.

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JAAune

1646 posts in 1784 days


#11 posted 11-14-2014 10:57 PM

The needed CFM depends upon the size of the spray booth. A larger opening requires more filter surface and more CFM.

Binks Airflow Reference

-- See my work at http://remmertstudios.com and http://altaredesign.com

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stefang

15512 posts in 2801 days


#12 posted 11-15-2014 09:02 AM

Thanks JAAune. I checked it out, but the terminology throws me. Not sure what he means by ‘Filter banks’ and he is talking about oil based finishes from the sounds of it. The back ‘filter’ wall on Jeff Jewitts’s little booth was about 5’ X 7’ and it had some side walls set at an angle to direct air flow towards the back wall.

-- Mike, an American living in Norway.

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JAAune

1646 posts in 1784 days


#13 posted 11-15-2014 05:33 PM

Sounds like 3500CFM would be ideal for that size of booth. It’s not necessary because you’re dealing with water-based products and aren’t dealing with OSHA. However, using OSHA standards will ensure you’ve got enough airflow to pull out the overspray and keep the shop and furniture clean.

The filter bank is just the area at the back of the spray booth that is covered in filters.

Binks makes a nice filter material which I’ve linked below.

AF Booth Filter

-- See my work at http://remmertstudios.com and http://altaredesign.com

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stefang

15512 posts in 2801 days


#14 posted 11-15-2014 10:00 PM

I’m thinking more like 2,000 cfm for the size booth I have in mind, although I can think that the bigger the better, but I don’t want to pay more for one than I have to. I was thinking about building a big booth, but I have changed my mind because I can’t do any really large painting upstairs in the loft anyway due to the difficulty of getting big stuff up there.

-- Mike, an American living in Norway.

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JAAune

1646 posts in 1784 days


#15 posted 11-15-2014 10:11 PM

Actually, bigger is not better. If the airflow gets too high, you’ll end up affecting the spray pattern and/or causing the solvent to flash off before it hits the wood (dry spray). You’re shooting for just enough airflow to pull the over-spray into the filters.

-- See my work at http://remmertstudios.com and http://altaredesign.com

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