Garage Paint Booth - Airflow help needed

E

Evil_Fiz

Promoted Users
I have built a "Dexter Kill Room" style paint booth in my 2 car garage. It is made up of four plastic curtains secured to the ceiling with furring strips and weighted at the bottom with 1" PVC pipe. The space is about 18' x 18' (3200 CF). I have 2 12" explosion-proof axial fans, rated at 2500 CFM each, venting through 16' ducts to the outside. The fans are pulling air through a box with 6 20" x 20" filters. The air intake is at the ceiling through the pull-down attic stairs. The opening is fitted with pleated MERV 8 filters. Lighting is provided by 24 100 Watt equivalent, 6500K LED bulbs, arranged in a rectangle around the paint area.

The intention is to put the air box at the furthest corner from the attic opening. This would pull the air partially over the car. Space is limited so this is the "BEST" configuration for mobility around the car. I am looking for feedback and suggestions on the best way to set up the booth.
- Is the airbox too big, too small, or adequate?
- Is the air path adequate or should I shoot for longitudinal airflow over the car?
- Would placing the airbox under the car be a better option?
- Any other thoughts or concerns?
Here are some pictures of what I am working with. The plastic curtains are rolled up and secured to the ceiling.

Attic door opening: about 21"x50"
Atic_Door.jpg


Picture from proposed location of airbox at furthest corner.
Fllor-to-Atic.jpg


Another shot from the corner of the booth
Wide_Shot.jpg


Airbox and fan
Air_Box.jpg


Thanks,
Emil
 
Looks like you have the right idea. I will tell you those cheap furnace filters wont capture much of the exhaust overspray. Ive tried them. You are much better off going with a true paint booth exhaust filter.
 
You need paint arrestor pads on your box rather than furnace filters. I've got a somewhat similar setup in my garage. First time I used it was to prime and paint a bumper cover for a Honda Civic. Epoxy, base, and clear. The filters were at least 75% stopped up just from this relatively small quantity of paint. Got some paint arrestors, and the next time I used it was to put a couple coats of epoxy on the front clip of my pickup. Couldn't tell any difference in air flow before and after with the pads even though this was easily 4X as much paint as I'd used on the bumper. 20x20 is a common size for paint pads so you wouldn't have to modify the size of your box.
 
www.autobodytoolmart.com

AFC Fiberglass Arrestor Roll Media

Having the Right Paint Booth Filter is Key for Proper Maintenance and Adequate Air Flow! Well maintained paint booth filters allow clean air to enter the booth plus remove overspray particles and mist from the exhaust air. Having a change-out schedule for your booth filters ensures proper...
www.autobodytoolmart.com

this is what i buy
 
  • Like
Reactions: MJM
How close are your neighbors? Maybe you guys know if Activated Carbon filters are also needed, to remove the fumes.
 
chevman said:
How close are your neighbors? Maybe you guys know if Activated Carbon filters are also needed, to remove the fumes.
Click to expand...
Be VEWY,VEWY, QUIET... HOA is listening.
I have also looked at carbon filters but am unsure of how restrictive they can be. I am in a residential neighborhood so fume control is important. Are there any recommended carbon filters?


OJ86 said:
www.autobodytoolmart.com

AFC Fiberglass Arrestor Roll Media

Having the Right Paint Booth Filter is Key for Proper Maintenance and Adequate Air Flow! Well maintained paint booth filters allow clean air to enter the booth plus remove overspray particles and mist from the exhaust air. Having a change-out schedule for your booth filters ensures proper...
www.autobodytoolmart.com
this is what i buy
Click to expand...
Thanks for the link
-----
Emil
 
Another question for the experts... Is approximately 1 air exchange per minute suitable for a home booth?

-----
Emil
 
I found this back when I was building my spray booth:

How do you calculate spray booth airflow?

To calculate the amount of exhaust air needed for the booth, a simple calculation is used.

CFM = Booth Face Area in square feet multiplied by the required flow (typically 100 FPM)

For example, and 8 X 10 filter bank (80 square feet) would require an exhaust of 8000 CFM (100 X 80) to achieve the required 100 FPM velocity.

To calculate the existing velocity knowing the exhaust volume the following formula is used:

Velocity = Exhaust in CFM divided by the booth filter area.

For example, a fan that exhausts 9000 CFM with a 10 X 10-filter bank would have a velocity of 90 FPM.

Proper airflow is not only necessary for the protection of the operator, but is necessary to achieve the desired finish quality. Flow that is too low will not draw the overspray to the filters. Much of the overspray will end up on the part as dry spray (rough finish). If the flow is too high, solvent tend to evaporate too quickly resulting in dry spray.
 
  • Like
Reactions: MJM
'68 Coronet R/T said:
I found this back when I was building my spray booth:

How do you calculate spray booth airflow?

To calculate the amount of exhaust air needed for the booth, a simple calculation is used.

CFM = Booth Face Area in square feet multiplied by the required flow (typically 100 FPM)

For example, and 8 X 10 filter bank (80 square feet) would require an exhaust of 8000 CFM (100 X 80) to achieve the required 100 FPM velocity.

To calculate the existing velocity knowing the exhaust volume the following formula is used:

Velocity = Exhaust in CFM divided by the booth filter area.

For example, a fan that exhausts 9000 CFM with a 10 X 10-filter bank would have a velocity of 90 FPM.
Click to expand...
Thanks for the math. Now the fun starts!

The intake opening at the ceiling is 20" x 55". Compensating for obstruction from the stairs we'll call it 20" x 50"

- 20" x 55" / 144" = ~7.64 Sq Ft
- 20" x 50" / 144" = ~6.95 Sq Ft
- We'll call it 7 Sq Ft

The exhaust filter box (filter surface area) is 20" x 20" x 6".
- 20" x 20" / 144 x 6 = ~16.67 Sq Ft

Each fan is rated @ 2700 CFM. We'll use an optimistic 80% efficiency to compensate for the filters and ducts.
- 2700 CFM x 2 = 5400 CFM
- 5400 CFM x .8 = 4320 CFM

That would result in air speeds of:
- at the intake - 4300 CFM / 7 Sq Ft = ~614 FPM
- At the Exhaust - 4300 CFM / 16.7 Sq Ft = ~257 FPM

At face value, the numbers look acceptable. The limiting factor is the airflow profile. The car is about 65" wide but the intake opening is only 50" wide. The exhaust opening is 60" wide with 1 vertical face and 1 horizontal face. For now, I will only be spraying epoxy, high-build primer, and maybe poly-primer. Math is not my forte' so I am not sure of the impact on useful airflow of the dissimilar flow openings.

Since dry spray is not as big a concern at this stage:
- Is the airflow profile as critical as for color and clear?
- Will placing the filter box under the rar of the car have any beneficial effect?
- Does anyone know what the effective airflow would be?

Thanks for getting into the weeds with me,
Emil
 
I use a positive pressure booth set up. Of course I live in countryside on 7 acres so neighbors are not a concern.

Started out similar to what you are thinking but soon realized that without adequate airflow both on the intake and exhaust end, you get turbulence in the booth.

I doubled the size of my intake side filter bank and added two more 2400 CFM squire cage fans.

To keep things simple, I took the total booth capacity (Length x Width x Height) which is 3600 Cubic Feet. Then I calculated the necessary filter bank size so that I could move a "wall" of air through the booth and out the garage door. With the four fans putting out rough 8000 CFM it could technically changed the entire air mass in the booth 2 times per minute. However I use the garage door as my airflow control and keep it only partially open. Just enough to maintain positive pressure in the booth. Here in Arizona dust is a big problem, so I don't want any entering the booth.

When spraying, I can literally watch the overspray being carried out the door.
 
Evil_Fiz said:
Be VEWY,VEWY, QUIET... HOA is listening.
I have also looked at carbon filters but am unsure of how restrictive they can be. I am in a residential neighborhood so fume control is important. Are there any recommended carbon filters?
Emil
Click to expand...
I also live in a neighborhood and I've been thinking about building a permanate dedicated paint booth, so I've been doing a lot of research, even looked at the inflatable paint booths. They are actually very impressive, but thats not what I want. Here is what I came up with for exhaust filters. Comments are welcome.

taff-guard has a nice write up on filters here, including flow restrictions.
Guide to paint booth filters

EXHAUST FILTERS: ​

"Exhaust filters are located near the end of the booth, by to the exhaust fan. These filters trap over spray paint particles like solid and liquid aerosols. This filter is essential for protecting the workers inside the booth, outside the booth, and the environment from being exposed to highly toxic over spray particles. If that’s not enough than another purpose would be protecting your paint booth fans and stack from the build up of over spray contaminants.

Unlike the dual stage intake filters, its single stage for the exhaust air filtration used by most paint booths. The type of exhaust filter used in cross-draft and down-draft booths are the same but, they are found in different locations and configurations."

This link has their number one option on the list for exhaust filters in effectiveness, longevity, and they are still affordable. Amazon and others have them.
https://www.taffguard.com/andreae-accordion-filters

A better explanation
https://www.andreaefilters.com/our-technology/

Maybe some of the pros can tell us if this is all hype.
 
Last edited:
You must log in or register to reply here.
Back
Top