Hi all, I've been scratch-building a spaceship of my own design (check it out on my Instagram if you are interested: https://www.instagram.com/barracudabay/).
It's about 4 feet long and soon I'll be painting it. I plan to build a spray booth and I've never made one before. I'm familiar with the concept and have been referring to this article on the construction. (http://www.starshipmodeler.com/tech/pa_booth.htm)
My question is, for something this size I'll need a huge booth. I plan to build it out of foam core. But how many filters and fans will I need? Is one in the center of the backwall sufficient? Or is it so big that I need a few in a row? Thanks!
Jumbo Spray booth?
Moderators: DasPhule, Moderators
-
dreadpyrat
- Posts: 11
- Joined: Thu May 03, 2012 5:36 pm
- Location: San Francisco, CA
-
kenlilly106
- Posts: 1302
- Joined: Sun Jan 14, 2007 12:18 am
- Location: in the mountains
Re: Jumbo Spray booth?
For a paint booth the rough guideline is that you'll need a face velocity of around 100 feet per minute (fpm). To figure out the fan size you need to take this number and multiply it by the opening in the front of the booth.
Ex - your model is 4ft long so let's say a 5ft wide booth that's 2ft high
5ft x 2ft = 10 square feet (sqft)
10sqft x 100fpm = 1000 cubic feet per minute (CFM) <--- this is the minimum amount your fan needs to move to get 100fpm face velocity
Because this doesn't take into account any losses in the exhaust ducting or variation in fan speeds you're better off to go a little higher in the fan rating than getting one dead on.
If you can't find a single fan to pull >1000cfm then you can use two or more in a row to get to that number. I would dedicate an exhaust to each fan, this way you avoid them working against each other and possibly chocking the flow if one fan is slightly more powerful than the other.
Ken
Ex - your model is 4ft long so let's say a 5ft wide booth that's 2ft high
5ft x 2ft = 10 square feet (sqft)
10sqft x 100fpm = 1000 cubic feet per minute (CFM) <--- this is the minimum amount your fan needs to move to get 100fpm face velocity
Because this doesn't take into account any losses in the exhaust ducting or variation in fan speeds you're better off to go a little higher in the fan rating than getting one dead on.
If you can't find a single fan to pull >1000cfm then you can use two or more in a row to get to that number. I would dedicate an exhaust to each fan, this way you avoid them working against each other and possibly chocking the flow if one fan is slightly more powerful than the other.
Ken
-
dreadpyrat
- Posts: 11
- Joined: Thu May 03, 2012 5:36 pm
- Location: San Francisco, CA
Re: Jumbo Spray booth?
Wow Ken, that is fantastic info - extremely helpful! Three points of clarification:
1000 CFM? That is a ton! Most bathroom fans do between 50-100 CFM. Wanted to double check I'm reading that right.
2 fans in a row - you mean side by side?
dedicating an exhaust to each fan - you mean ducting away from each fan to the outlet point, rather than splicing them into the same duct work?
Thanks!!
1000 CFM? That is a ton! Most bathroom fans do between 50-100 CFM. Wanted to double check I'm reading that right.
2 fans in a row - you mean side by side?
dedicating an exhaust to each fan - you mean ducting away from each fan to the outlet point, rather than splicing them into the same duct work?
Thanks!!
-
dreadpyrat
- Posts: 11
- Joined: Thu May 03, 2012 5:36 pm
- Location: San Francisco, CA
Re: Jumbo Spray booth?
Though I could get one of those $20 box fans...they move around 2500 CFM...
-
kenlilly106
- Posts: 1302
- Joined: Sun Jan 14, 2007 12:18 am
- Location: in the mountains
Re: Jumbo Spray booth?
It is. For spray booths it's all about face velocity to pull the fumes in and across the work and out the back. We have some lab booths at work and to get that kind of velocity the fan unit is about the size of a 5-gallon bucket and sounds like a turbofan engine.dreadpyrat wrote: ↑Mon Mar 19, 2018 7:20 pm Wow Ken, that is fantastic info - extremely helpful! Three points of clarification:
1000 CFM? That is a ton! Most bathroom fans do between 50-100 CFM. Wanted to double check I'm reading that right.
2 fans in a row - you mean side by side?
dedicating an exhaust to each fan - you mean ducting away from each fan to the outlet point, rather than splicing them into the same duct work?
Yes, side by side or one on top of the other, all depends on how the booth is constructed. I would center them though as best as I can so they pull evenly across the entire opening.
Duct from each fan to the outlet. You might be able to run each fan into a larger, common duct to exhaust the flow. I would not use the same size duct as you did from each fan.
-
seam-filler
- Posts: 3924
- Joined: Thu Apr 17, 2003 11:05 am
- Location: Aberdeen, Scotland
Re: Jumbo Spray booth?
Also consider what paint you're spraying with. Although any airborne particles can turn explosive, this is much more important with lacquers and solvent-based paints. One spark from the coil of a fan could be bad news. If you're spraying a lot of solvent-based paint, you may want to look at explosion-proof or spark-resistant fans - but they can get seriously expensive.
"I'd just like to say that building large smooth-skinned models should be avoided at all costs. I now see why people want to stick kit-parts all over their designs as it covers up a lot of problems." - David Sisson
Re: Jumbo Spray booth?
Yes but ducting one down reduces the flow through unless you want a 18in hole to the outside. Hence the cost of high cfm blowers.dreadpyrat wrote: ↑Mon Mar 19, 2018 7:27 pm Though I could get one of those $20 box fans...they move around 2500 CFM...
To answer dreadpyrat, yes this would mean more fans across the back. When exhausting remember to keep the ducting volume equal or larger. A standard 4in duct has an area of about 12.5 square inches which means a 1x12.5in slot is the same, providing you can taper that circle into a long rectangle.
Abolish Alliteration
-
dreadpyrat
- Posts: 11
- Joined: Thu May 03, 2012 5:36 pm
- Location: San Francisco, CA
Re: Jumbo Spray booth?
Thank you everyone, I really appreciate this help. So it sounds like using a large box fan and tapering down from the fan to a standard Dryer duct hose doesn't work due to the severely reduced flow. My outside outlet is about 6x12 inches - one of those typical air outlets along the base of a garage wall. I'll be spraying only acrylics and maybe the odd enamel clear coat.
Since I'm not going to be flooding the booth with paint, despite the size of the model (I'll be painting mostly detail work in different areas), am I being naive to think that 1000CFM might be overkill? forgive me for questioning the math, but its hard to imagine such a tiny amount of painting needing such a huge amount of air removal.
Since I'm not going to be flooding the booth with paint, despite the size of the model (I'll be painting mostly detail work in different areas), am I being naive to think that 1000CFM might be overkill? forgive me for questioning the math, but its hard to imagine such a tiny amount of painting needing such a huge amount of air removal.
-
kenlilly106
- Posts: 1302
- Joined: Sun Jan 14, 2007 12:18 am
- Location: in the mountains
Re: Jumbo Spray booth?
I think you could build a reducer out of cardboard or something like that to go from the box fan to the 6x12 opening.
1000CFM was only a guess based on the size of your model. 100fpm face velocity is the industry standard to ensure the airflow is pulling the paint and fumes away from you and out the back.
In the end it's up to you to build (or have built for you) a booth and fan that is sized correctly for your application.
Ken
1000CFM was only a guess based on the size of your model. 100fpm face velocity is the industry standard to ensure the airflow is pulling the paint and fumes away from you and out the back.
In the end it's up to you to build (or have built for you) a booth and fan that is sized correctly for your application.
Ken