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So I'm moving on with the workshop build and it's time to decide how to configure the airflow in my spray booth.
The 2 easiest options are:
A - make the air flow directly across the room
B - put intake near ceiling so the air flows on diagonal

I think technically option A might be better, BUT with option B I can put a storage cabinet on the other side of the wall.
Are there any problems with putting the intake higher?

I'm also wondering about the size of the intake filter. Any recommendations on how to calculate it?

The booth is framed out already and the size is W 5'8" x L 8' x H 10'

both will work but you would want to have something more like a table depending on your CFM.
this is what I made I created a down draft table . There something you need to consider and that is
the VOC. You are not controlling all the air I also have a voc vent to pull them out of the booth
https://www.youtube.com/watch?v=escxSMDoC5g

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Can't definitively answer on options A or B, although I use B, but a linear flow is of course not guaranteed by either setup.
But advice I've seem on air intake filter area is 3 x exhaust filter size, given that adequate air velocity is met.
My setup is also downdraught with guitar horizontal.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

After checking out the prices on those explosion proof fans... It seems that getting the whole room to move air at 100 ft/min will be cost-prohibitive.
I can get a good deal on a used 12in high-pressure explosion-proof fan that moves 1600 cfm.
So let's say it loses about 25% of that due to filters/ducts/etc and I'm left with 1200 cfm
That would leave the working "face" with air velocity 100 ft/min roughly 3x4ft.
Seems like that would be enough, no?

About VOC vent - since vapors are heavier than air, some sort of duct along the bottom wall with a few intake holes?
Does this also need to have explosion proof ventilator? I assume you would turn some time after spraying when most of the fumes are gone anyway, but i just want to be on the safe side...

A 12" explosion proof fan from Dayton is what I'm using. I have a bit over 6 sq ft of standard HVAC filters arranged behind/below the spray area. It seems to work well for me. After I spray nitro I can barely smell it when I take my mask off. My booth is about 5' x 6' with no door.

I have a drying cabinet but it is not vented. I wish it was.

_________________
Steve Smith
"Music is what feelings sound like"

Not all vapors are heavier than air. It has been my experience that lacquer vapors are somewhat neutral and will be dispersed throughout the air column. Especially since you will have the fan stirring up the air.

VOC are heavier than air and are harmful to your health yes there are other fumes. If you look at the video I have 3 fans
one on the down draft table
then 2 4 inch fans one low for the VOCs one high level with the table to emit the fumes. Get the bad air out . If you have a sealed booth
you can use a lower CFM fan. Figure about 1 volume exchange every 2 min to vent the room. After 20 min most of the fumes are out.
You can never be too careful.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

What finish do you intend using?

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

nitro

Full precautions then..........

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

A few thoughts to share:

1. I think it is important to differentiate between the different reasons why you want to keep good air flow in the booth, and then see how your design choices affect each one. In no particular order, I think there are three goals. First, you want to keep the vapor concentration low so that, on the off chance there is a spark, you don't blow up. Second, you want to protect your workpiece from too much dried, airborne finish landing on it from the overspray. Third, you want to protect your lungs from being exposed to too much of the finish material (although your PPE is the main defense against this danger). As I said, think about how going with something less than 100 feet/minute will affect each of these three goals.

2. Pay attention to the size of the motor that drives the fan you are considering, and how the size of the motor affects the CFM rating as static pressure increases. The Grainger website (the section that gives choices about which Dayton tube axial fans to use) gives some very useful information about this. Essentially, if you are using a very low horsepower motor to drive the fan, the CFM rating will drop dramatically as static pressure increases. The 25% loss you are anticipating may be too low of an estimate, depending on the horsepower. Food for thought.

3. When you buy quality, you only cry once. You are about to make choices regarding personal safety when using toxic, flammable materials. Is this where you want to save money? I'm not saying a full blown commercial booth is the right choice, but spend your money where it makes the biggest difference. For me, it was the fan and the motor driving the fan.

Good luck with the design of your booth.

I have to take back something that I said. I looked up MSDS sheets for several manufacturers of nitro and some of them do state that the vapor is heavier than air so they can settle in low areas. But we must remember that lacquer has several constituents. One of which is denatured alcohol which is lighter than air.

Laminar air flow (meaning no mixing of currents) is very difficult to achieve and not really what we want for a spray booth. I feel fairly confident that airflow of most any spray booth will be very turbulent which is desirable because it will sweep out vapor accumulation in low areas.