Paint Booth Ideas

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PostPosted: Wed Oct 26, 2016 9:09 am
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Hello Everyone,

I plan to build a paint booth in my out building this week and was wondering what you guys /gals think is better, positive or negative pressure system. Above is a sketch I made of my idea for a Negative booth. I could also switch the fan and filter locations to make it positive pressure. On one hand, I like the idea of the Negative booth because no air is blowing directly over the car. One the other hand, I'm not sure if sucking fumes through $20 Home Depot fans could cause an explosion. I read somewhere where someone said I would never create enough fumes to be a problem. Not sure if that is true. Has anyone used basic fans to pull fumes out of the work area. The booth will be constructed using 2x4 's and 8mil clear plastic. I'll seal all cracks and joints with duct tape to get it as air tight as possible similar to the second image. Any tips and ideas are welcome.
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PostPosted: Wed Oct 26, 2016 9:45 am
Do a search on Homemade Paint Booth and you should come up with a ton of information on this. I have put formulas for calculating air flow needed, filters sizing etc. on here.

The fumes are extremely flammable and should not be dismissed as nothing to worry about.

The benefit of a positive flow booth is that the fans are drawing fresh air and pushing the the fumes away rather than drawing them in.

Also, be sure to have your booth flowing air before opening and mixing flammable products.
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PostPosted: Wed Oct 26, 2016 10:34 am
My brother just told me I could have a squirrel cage motor and blower assembly he saved from a furnace that he replaced at his house. I think I will use this instead of the Plastic box fans.



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PostPosted: Wed Oct 26, 2016 10:37 am
I find positive pressure easier. Positive pressure keeps dust from coming in through cracks unfiltered. Therefor you don't have to worry about getting it perfectly sealed. Good size exhaust duct run to the outside will keep most of the fumes out of the building.

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PostPosted: Wed Oct 26, 2016 11:19 am
Here are some figures I copied from a spec page for a commercial booth supplier.
Notice the velocity for a side draft is figured at 100 ft/min. and the downdraft at 50 ft/min. Either way you look at it the air is moving right along howbeit en masse.

Paint Booth Airflow Calculations

Scenario #1 - Air moving from ceiling at back of booth to the exhaust filters at far end of booth.
Based on these assumptions:
Surface area (ft2) = 4.4m (wide) x 2.2 m (high) x 10.76 (m2/ft2)
= 102.4 ft2
Air velocity = 102.4 ft2 x 100 ft/min

= 10,240 ft3/min
Scenario #2: Air entering at ceiling and moving downward toward the filters immediately above the floor along the sides of the booth.
Based on these assumptions:
Surface area (ft2) = 6.6m (long) x 4.4m (wide) x 10.76 (m2/ft2)
= 312.5 ft2
Air velocity = 312.5 ft2 x 50 ft/min

= 15,625 ft3/min
If you want uniform air distribution throughout the booth you should size the air intake filters accordingly. If you make the filter section too small, you can expect turbulence in the booth and this will cause paint overspray to settle on the walls, ceiling, lamps, etc. In addition, turbulence lowers transfer efficiency.


To put it in very basic terms let's use a 10' wide x 10' high x 10' long paint booth.
10x10x10 = 1000 cubic feet of air in the booth.

10 wide x 10 high = 100 square feet of surface area

Surface area x required air velocity = fan size

100 sq ft x 100 feet per minute = 10,000 CFM
This is where it gets real expensive in a hurry to construct a professional paint booth at home. This changes the air 10 times per minute.
What I did was opt for something functional but not up to OSHA standards.

Taking the total capacity of our 10x10x10 example booth and changing all the air 3 minutes.
1000 Cubic Feet x 3 (air changes per minute) = 3000 CFM fan size

Let's consider a 10' high by 15' wide x 26' long booth.
10x15x26 = 3900 cubic feet

3900 cubic feet x 3 air changes per minute =11700 CFM fan size

My booth is 3600 cubic feet and I have 4 squirrel cage fans rated at 3000 CFM each.
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PostPosted: Wed Oct 26, 2016 11:47 am
Sounds like good advice. I'm going to go with the positive pressure system to keep the dirt from entering through any cracks. It seems like a more reliable system. Thanks again.

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PostPosted: Wed Oct 26, 2016 6:30 pm
So 68' , I am trying to understand some principles here....Is your booth a negative pressure with all 4 squirrels pulling air out or do you have two fans pushing in while two pull out to equalize the flow? I am trying to figure out how you set it up without creating a wind tunnel. Also, could you explain to me the difference between a fan with an enclosed motor vs. a sealed motor? I know you advised me to just buy a manufactured paint booth but I am tossing the idea around of devoting 20% of my mechanics shop to a paint booth area....one reason being is the shop is already heated thus I could draw warm air into the booth for painting in the winter. If I did this I would have to build my own booth due to the height of the ceiling. Could you provide the link to when you built your booth? I read it once but can not find it again.....thanks....John
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PostPosted: Wed Oct 26, 2016 11:45 pm
I have 4 fans blowing fresh air into the booth and exiting at the other end.
Reducing turbulence (when not using fans to draw the air out) requires a large filter bank so that you are virtually moving a "wall of air" from one end of the booth to the other.
My fans blow into a homemade plenum which still needs design improvements to eliminate back flow through the filters.

Trust me when I say to go with a manufactured booth. I have been messing with this thing for years and each time I think I solved one problem something else pops up.
Yes it works and I get by with it but for the man hours alone it would have been cheaper to buy one.

I suggest you ask the pros what they think of their booths so you can find a brand that people who use them everyday are happy with.
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