Activated Carbon Filters - Experience?

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Forum topic by Crashcup posted 02-16-2017 06:00 PM 391 views 0 times favorited 10 replies Add to Favorites Watch
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24 posts in 980 days

02-16-2017 06:00 PM

Hi, wanted to see if anyone on this forum has used activated carbon filters (same thing as charcoal filters?) on the exhaust side of a spray booth.

I’ve read a lot of threads and got a lot of good advice from others on here, but I don’t think I’ve seen this discussed. I’m just trying to put together a plan to have spraying capabilities in my detached garage. I want to be able to finish not only wood projects, but also paint motorcycle parts, car parts, or miscellaneous shop stuff. (I have a couple of work tables I bought at an auction for use in my shop, and have been repainting with rattle cans – which made me think more about this). I don’t expect I’d ever paint a car out there, though.

Being in Minnesota, winter is a tough time to maintain the right conditions for spray finishing. If i put together a DIY paint booth and exhaust the booth outside, it’s going to be hard to keep the garage warm enough. If I try recirculating the air in the garage, I risk building up an explosive mixture – not good with an open-flame propane heater.

So I know activated carbon is supposed to absorb (or adsorb??) VOCs from finishes. That’s theory, but I’m not sure how much they actually remove. I’m wondering if it’s even feasible to consider recirculating the garage air, if the booth exhaust air went through the usual paint filter for solids, then through a carbon filter.

Any direct experience or knowledge on this would be most appreciated!


10 replies so far

View Dustin's profile


359 posts in 521 days

#1 posted 02-16-2017 08:41 PM

So, you got me curious, and I did manage to find this test conducted on the efficacy of activated carbon removing VOC’s in general (in this case, benzene and formaldehyde from cigarettes):

As for experience, I think you may be more likely to get anecdotal experience (or even possibly people seeing it used in an industrial setting), but I don’t think the average user has the $3k + to shell out for the fancy VOC meter used in these tests.

Hope this helps.

-- "Ladies, if your husband says he'll get to it, he'll get to it. No need to remind him about it every 6 months."

View Fred Hargis's profile

Fred Hargis

4641 posts in 2273 days

#2 posted 02-16-2017 08:56 PM

They do absorb the VOCs, and what you propose will work….for a short time. The carbon will loose it’s effectiveness, most likely in a short time. What you plan might be an expensive solution…..but it will work. If you want to prove this (that it works) for your self, it’s easy. Put the activated carbon filters on your respirator, and then step into an area where you’ve been spraying a finish with VOCs. You won’t smell anything; that is, until the filters are used up.

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

View bbasiaga's profile


978 posts in 1775 days

#3 posted 02-16-2017 09:04 PM

I can chine in on the industrial side. You’d need to figure out how much carbon you needed to absorb the VOC and last for X hours of service. After those hours, you have that hauled off an replace it with new carbon. It’s expensive and typically only used for polishing type steps, not bulk removal. If exhausting the air isn’t feasible, a full time use of a respirator may be your best bet. Or find a final is without the VOC content.


-- Part of engineering is to know when to put your calculator down and pick up your tools.

View ClammyBallz's profile


422 posts in 917 days

#4 posted 02-16-2017 09:06 PM

I agree with Fred. Plus the finer particles will clog the carbon filter faster and make it much less effective.

My spray booth vents outside, I crack the door a inch to let a little air in when spraying. Most of the time I’m done in 5 minutes and the shop only drops about 5 degrees for a short time.

View Crashcup's profile


24 posts in 980 days

#5 posted 02-17-2017 01:05 PM

Thanks for the replies.

Clammy – interesting that you don’t get as much temperature change as I would have thought. Do you have an idea of cfm your exhaust fan is moving? And what’s the volume of your shop space?

Brian – I already use a 3M half-mask respirator with organic vapor cartridges, so that’s covered. I’m thinking more of keeping the concentration of fumes down enough to prevent ignition.

I may try to get some more information yet on this, but it’s looking like it wouldn’t be too practical. Another aspect for me is the heat source. Right now I’m just using propane space heaters, but I have a hot water boiler I saved from our house remodel. If I use that, and install the boiler in the lean-to shed behind the garage, it would separate the burners from the air in the garage to eliminate the risk of fire/explosion. But, not sure when I’ll be able to get to that!

View ClammyBallz's profile


422 posts in 917 days

#6 posted 02-17-2017 06:12 PM

My spray booth has two 5 ton blowers, around 2000 CFM for each blower, 4000 CFM total. The shop is 4000 sq ft. I should add that my shop is on the 2nd floor and stays around 55-59 without the heat on in the winter due to the floor being heated from the 1st floor. I set the electric heaters to 68 when I’m in the shop. If it’s 30-40 outside, it will drop from 68 to 64 while I’m spraying. Again, my door isn’t wide open, only cracked an inch.

View EarlS's profile


519 posts in 2128 days

#7 posted 02-17-2017 06:26 PM

Propane heater and VOC’s are a recipe for a big boom. I think the folks that talk about cracking the door open a bit or the window are on the right track. I use a box fan with a furnace filter over it to pull the air out of the shop through a window with the window opposite it open slightly to create a draft through the area.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

View Crashcup's profile


24 posts in 980 days

#8 posted 02-17-2017 06:53 PM

My spray booth has two 5 ton blowers, around 2000 CFM for each blower, 4000 CFM total. The shop is 4000 sq ft.

Holy cow, 4000 sf! Makes my garage sound like a shack!

That size may have something to do with the temp not dropping so fast. Assuming 10ft ceilings, that’s 40,000 cf. If your door is just cracked, the blowers may not be pulling their rated flow. But assuming they are moving 4000 cfm out, they’d have to be pulling 4000 cfm in. That’s an air exchange of 0.1 per minute.

Based on recommendations I’ve seen for a linear flow rate of 100 fpm in a cross-flow both, the small booth I’m envisioning would need 7200 cfm.
My garage is only about 6240 cf, so that would be an exchange rate of about 1.2 per minute. Over 10 times higher rate, so I think I might lose heat a lot faster than your shop.

It’s making water-borne finishes sound more and more like the way to go. I’ve always had a bias toward solvent-based as being more durable… and I know water-borne is way better than it used to be… but I’ll have to try them for myself.

View Crashcup's profile


24 posts in 980 days

#9 posted 02-17-2017 07:20 PM

Here’s a totally unresearched thought off the top of my head: could the fumes from spraying paint/lacquer/varnish be burned off?

My propane radiant heater has a fine screen that the gas flows on to for burning… could a similar approach be used to run the spray booth fumes through?

I’m sure there are a hundred safety and environmental concerns. But if it could be worked out safely it would have the double benefit of removing the fumes and ADDING heat to the shop.

View Lazyman's profile


1240 posts in 1167 days

#10 posted 02-17-2017 07:36 PM

Brian – I already use a 3M half-mask respirator with organic vapor cartridges, so that s covered. I m thinking more of keeping the concentration of fumes down enough to prevent ignition.

- Crashcup

If you are spraying enough paint in a confined space that ignition is a concern, then you definitely need to vent it to the outside. Even if a carbon filter can absorb some of the flammable gases, think about how much of it there is in liquid form in the paint (some propellants in rattle cans are very flammable too) that it would have to absorb to actually prevent it from building up in the confined space. Some of them may be oderless so you wouldn’t even know if the filter was working. Some finishes that you spray also atomize into the air and can be flammable in that form but you can use paint arrestor filters to capture most of fine airborne droplets—again, if you are spraying enough for ignition to be a concern, vent to the outside.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

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