Range Hood Placement for Spray Booth?

Thanks again guys! Yeah, I think I will go with the original set up, and add a large exhaust fan in the window of my modelling room too. And I like the aluminum ducting suggestion. Much better than the cheap dryer vent stuff. And I will definately check all of it often and keep it all clean.

James

Gip, you definitely sound like you know what you're talking about. I agree with everything you've written (not that that's woth anything...). And highlight one thing that you said... plastic flexible dryer vent hose is a KILLER for airflow. At a minimum use the flexible aluminum stuff (i don't know what it costs, but it's pretty cheap), but preferrably solid aluminum vent. Otherwise, your fan investment is just useless.

Why's my head getting sore??

Murray

The whole reason spray booths were put into industrial environments were for the prevention of fires and explosions due to the high concentration of flammable/combustible vapors accumulating in a work space over time. But this brings us back around to the frequency/duration issue. Most industrial booths are for the high-volume paint guns and rattle-cans that are being used for several hours a day. Fires occur because vapor-air concentrations are at their best, and then when you introduce an ignition source...well, you get the picture. Paint residues accumulating on fans, filters, and booth sides is also an issue; that's why booth construction should not be out of wood. Fires are contained better in metal structures. Based on the fact you are just airbrushing, and that your frequency/duration is minimal (compared with an equivalent industrial day), you could probably get away with a sparking fan, provided you are moving enough air to keep vapor concentrations at a minimum--which they should be. But keep in mind that you still have to have a fan capable of moving enough air to remove the vapors you are creating, and in addition, push them through a length of duct to the outside. I'm not going to suggest a 1,000cfm fan, but I DO think that a 180cfm range hood is not enough to effectively accomplish what you want to do with the size of the booth you want to do it in. Personally, I would not look at anything less than about 400-500cfm. That will give you an average of 50 fpm at the face, and should adequately move most of your paint vapors. You should also do what is necessary to keep your exhaust ducting as short and with as few bends as possible. There is still going to be a big static pressure fall-off on the exhaust side of the fan, and you need to push out what you sucked up. Short ductwork and a straight exit will help with that effort, and will prevent vapor accumulation inside the duct....which could be more of a problem with a sparking fan than just exhausting vapors past it. The duct should also be as horizontal as possible (not vertical), and not be constructed of such combustible stuff as dryer hose. Lastly, for the fan to work at its most efficient, it needs to be positioned at the back of the booth. If you mount it on top, a small baffle hung inside the booth will help to even out the airflow.
Murray may have a point. It may be even more efficient to have a multi-fan setup instead of a single fan. The necessity for good CFM still doesn't change, however.
You'll probably be OK unless you pull out several rattle cans and start using them 8 hours a day...in which case we need to have a talk about booth design...
James, you've got the option of venting a room (the cheap, easy way to go), and the option of building a booth. If you go with a booth, make sure you inspect and clean it regularly....and keep a fire extinguisher nearby as a measure of protection, and you should be OK.
Let us know what you decide to do. This is a learning experience for us, as well!

Gip Winecoff

PS Excuse me, but I have to go knock on Murray's head...

James,

Here's my personal thoughts/experiences and they are sure to clash with others...

Personally, I've never heard of anyone's hobby booth exploding. Heard lotsa talk, but never heard of it happening. Not to say that it hasn't, so you have to make your own call. If someone has experienced this, please share the story...

I'm no techno expert, but I think the 'spark' hazzard has to do with when the fan is either powered up or down. If you power up the fan before you spray, and let it run aftwerwards, then it may not be a real issue. I really don't know for sure though, so maybe someone else will provide better info.

Personally, I had three muffin fans in my booth (larger than computer fans, they were about 5" square) and I never had any problems. Maybe I was flirting with death... I have no idea. I would routinely spray straight lacquer thinner through my brush for cleaning and didn't have any problems.

That all said, maybe I'm extremely lucky ?? (Knocking on head now...)

Murray

Styrene, don't worry, I did not take any of it that way. I appreciate the help. Wasn't looking for a bunch of "yes" men when I posted.
That's what's great about these boards and newsgroups, etc... There is a wealth of information out there. You just have to ask.
Which I did.

Mike - both acrylic and enamel. Plus thinner, lacquer, whatever to thin, clean, etc...

As for the booth - I am not to concerned about venting the booth and room at an extreme level. I figure it it does it pretty good, then that's acceptable to me. I was planning to get one of those paint/hazardous fumes masks (the ones where you change the filter media from time to time) so I am not really worried about breathing in toxic stuff. And I don't think an airbrush, for the amount of use per session, will generate that much anyway.
The part I am concerned about is fire/explosion. A few people are saying get explosion proof fans with brushless motors, etc... to avoid it. Because many fans, that have brushes, can sometimes produce sparks which can ignite the toxic fumes produced by enamels, thinners, lacquers, etc... But range hoods don't even give those specs when you are checking them out to buy one.

I know range hoods are designed taking into account hot air, grease, oil, etc.. but not toxic fumes (excluding my ex's cooking, that is - LOL!) I believe, so don't know if there are brushless ones or not. Other factors may include whether or not the motor is in the direct path of the (vented) airflow. And then there is the light that comes with a range hood. Is that a potential problem.?

Still lots of questions. LOL!

Anyway, i will keep looking around. Any appreciate any and all comments and suggestions. Besides, I am sure we are not the only ones reading this thread so all the info will help others as well.

James

James,

What kind of paints are you going to be using?

If you use acrylics exclusively this problem will be easy to solve, but if you are using enamels or lacquers it will be more difficult as has been discussed already.

Mike

Yes on the respirator! Good call Gip! I missed that too. I don't often use mine when I'm just airbrushing because the booth does a decent job of clearing the air. However, whenever I get a rattle can out, I always put on the respirator. And, I open the room window as well (unless it's winter...).

Keep us posted on what you go with James! The fact that you're aware that you need ventilation is a good thing. Gip's got good advice and ideas.

Murray

James,
You know, ventiing the room may be a viable option. Factoring in the frequency and duration of your painting along with the volume (which isn't a whole lot with an airbrush), a large exhaust fan in the window, and maybe a small fan behind you when you spray would provide enough dilution ventilation to reduce any potential health hazards associated with spray painting. I didn't tell you this, but I don't use a spray booth. I simply open a window and room door, and turn on my ceiling fan. While this in not ideal, it still works. I am only using about 2/3 of a color cup full of paint for most of my 1/35 armor. Priming, base coat, and running a little thinner through the brush for final cleaning leaves a slight to moderate odor in the room that quickly dissipates. By the way, smelling a solvent doesn't necessarily equate to overexposure. Many solvents have an odor threshold at several ppm, while exposures occur at 10 times that amount (speaking VERY GENERALLY).
You could also, if desired, spend $20 and get a good respirator to go with that window unit. Going this way will probably save you several hundred or more dollars when all is said and done and still offer the protection and safety you're looking for.
I apologize for not thinking of this sooner, and any appearances of hypocrisy on my part. You mentioned spray booth, and that is all I focused on. Keep us posted on your decisions and outcomes.
Gip Winecoff

James,

You are right that a 'perfect' booth is probably not as common as a simple cheap set up. However, ANY ventilation is better than NO ventilation, so whatever you can do will help. My last booth had 3 muffin fans in it (all in a row). It actually worked fairly good, but it didn't clear the fumes as much as I wanted, especially when I was using a spray can. For airbrush use alone, it worked pretty good.

As for the whole 'explosion risk' issue... well that is a reality. You need to make your own choice about that.

My advice would be to get the fan that has the largest cfm you can afford, and then build your booth around that. You already know it's not going to be what the 'industrial guidelines' would call for, so get as close as you can.

Good luck

Murray

Here's one that a "spray booth" article referred to:

http://www.computergate.com/products/item.cfm?prodcd=BCFAC12B

The booth article is at:

http://www.geocities.com/budb3/arts/paint/sprbth.html

read it and tell me what you think.

Not a lot of info on the fan, so will have to do more checking.

James

Opinions on "Muffin Fans"? Can these be ducted? Maybe a few of these would be better that the range hood.

James

I know. A 1000 cfm does seem rather unattainable in reality for the size of booth I want. You would be building the booth "out of" fans. It is also cost prohibitive. At least for me.

What do most people, that have airbrushes, do? And as we all know, there are thousands of them. I can't see most of those people with large expensive ventilation systems.

I gather most just do what they can afford and hope for the best.

James

This is all a tough choice. Any type of ventilation is better than none. And the more the airflow, the better. I tend to use enamels and lacquers, so I'm after as much airflow as I can get. Direct ventilation to the outside would always be my preference and is probalby cheaper/easier than trying to vent an entire room. I had a small booth with 3 seperate 80cfm fans in it. I thought it would be plenty of power, but I didn't like it. You have to remember that the type of ducting and all of the corners and filters really consume alot of the 'cfm'. I don't remember all of the detailed calculations, but the reality is that if you've got a 200cfm fan with a flexible vent hose and a filter attached, chances are that the final cfm at the front of the booth isn't a whole lot better than about 40-50cfm. If you can, use a solid sheet metal vent with as few turns/corners in it as possible. It might cost a bit more, but the end result is much better.

To each his own (health risk that is...), but I have a new fan that's something like 380cfm for a relatively small booth. I'm hoping that it will be enough once I get everything set up, and plan to have as little air resistance as possible for getting those fumes out of my house! Getting 1000cfm is a pretty tall order, but technically is what would do the best job at venting a booth the size you're talking about. You have to make your own choices, but personally I would try to get more air movement than what a range hood is going to give you.

Murray

Thanks again! Well, I looked around a bit on-line today, and the fans (explosion proof, brushless, high CFM,...) I could find that match what is required were huge (and expensive). I think some were designed to go on the roof of a nuclear reactor. LOL!
Unless I am not looking in the right places.

Question - Do I have to vent the booth? Or can I vent the room instead? I am thinking that the appropriate fans are probably to large for the booth I have in mind. Is it feasible to put a large exhaust fan in the window of my separate modelling room?

I don't think an airbrush, for the amout of spraying I will be doing, would generate that much fumes anyway, so...

Opinions?

James

P.S. I agree, very interesting stuff.

James,
Reducing the open area on the front of a booth the size of yours, with the fan you are suggesting may only increase face velocity by a fraction, but does nothing for capturing all the vapors and transporting them through a duct. In designing ventilation systems, most engineers (which I ain't) will add about a 25% increase in total cfm after calculating booth size, face velocity, and static pressure loss through the duct (dependent upon diameter, length, number of elbows, etc.). I would ROUGHLY estimate a fan rated at about 1,000-1,200 cfm should fit your needs. The booth you are trying to build (based on your size requirements) almost borders on, IMHO, a commercial/industrial application. I apologize for not knowing where to direct you in terms of fan types, catalog numbers,etc., but it would seem that industrial supply businesses should know about, or have access to the products you need. You may also find it cheaper in the long run (if liabilities and insurance considerations are an issue based on renting or owning ) to purchase a booth, rather than build one. Pre-built booths will--or should--have all the features you want, plus they should carry some sort of approval or certification so you can paint away knowing your pride and joy won't catch fire in the middle of a measure 32 paint scheme. Depending on the booth, they may also come with the right filters and baffles, which will distribute airflow evenly throughout the booth so there won't be any dead spots when you're painting. For me this has become quite an interesting thread. Please keep us informed as to what you decide to do, and what results you finally come up with.
All the best,
Gip Winecoff

I have about half the front openning of my hood covered with clear lexan, this reduces the open area, and increases the flow.

I say... give your plan a try, but think about how to reduce the open area on the front.

Well I don't want to decrease the size as I have some ship kits that have 30 to 40 inch hulls to paint. So, what kind of fan would I need? I have read that bathroom fans are not appropriate. Axial? Any recommendations? Brand names, Model numbers?

And if I lose the booth I will need lighting also. Any recommendations for that? Brand names and model numbers would help as I am not a tech person. Also, don't want to spend a fortune either.

Thanks in advance,

James

Recommended airflow for a booth spraying combustible/flammable vapors is 80-100 fpm at the face. If your booth has a face area of 8 square feet (2' X4'), that works out to a range of about 640-800 cfm needed to adequately exhaust your paint vapors. First, (and I could be completely wrong here) , but I don't think a fan rated at 180 cfm is going to give you adequate airflow, and secondly, mounted overhead is only going to add to your woes. Adding in pressure drop based on the length of your ductwork, you may be throwing money down the drain. On the other hand, decreasing the size of the booth, trashing the range hood idea, mounting a good fan at the bottom of the booth, thereby creating a downdraft exhaust...results in lower cfm requirements, vapors actually captured and exhausted, a safer work area, etc.etc.
Gip Winecoff

The 1-1/3 X 10 inch is a flat rectangular duct designed to run up inside a standard wall made with 2 X 4s.

The 7" round is pretty standar... that's what mine is. Look for flexible aluminum pipe... it's a lot easier to make it fit, and not much more expentive. These look about 2 feet long but stretch out to about 6 feet.

Thanks for the responses. I will probably mount the hood on top. It would seen the easiest way to go. Not to keen on mounting it at the back. Then the fan, and light, would be right in the line of fire of the spraying.

The Hood is not an expensive one. Only $46.99 at Canadian Tire. It's the 30" Broan Basic Performance one. Front rocker switches for 2 speed fan and built-in covered 75 watt light.
1.7 amps,/ 120 volts. Says it draws 180 cfm and has a sound rating of 7.5 sones. (I gather that is kinda loud, but since I am single, it's probably not to bad)

Doesn't say what kind of fan. But for the price I am not expecting top of the line.

Will have to check for the ducting. It says it takes 3 1/4" x 10" duct for either vertical or horizontal ducting, or 7" round duct for vertical ducting.

Can anyone explain what they mean by 3 1/4 x 10? The 7" round seems self-explanatory. Is the other one rectangular metal ducting?

Either way I gather I will need about 6 to 8 feet of the stuff.

Thanks again guys.

James

P.S. Hey naplak, I am sure I have seen you somewhere before. LOL!

Gip brings up a good point. Are the motors in these exhaust fans brushless or at least out of the path of the air moving through them such as a squirrel-cage fan is?
I would think they would have to be since they are designed to vent grease from cooking on the stove and it is flammable, although not near as flammable as lacquer.

Mike

A range hood is a canopy hood, and as such, is designed to exhaust heated water vapor that is already rising. Paint vapors are heavier than air, so mounting the range hood overhead is probably not the best way to go. It might be better to turn it on its side and place it in the back of the booth. This position would also give you a more linear air flow. Also, a word of caution: (1) Paint booth walls should be made of non-combustible materials. Wood ain't it. (2) Any fan used for exhausting paint vapors should, at a minimum, be brushless. Remember that paint vapors are flammable, and any vapors in contact with a sparking electric motor dramatically increases the risk of fire.
Gip Winecoff

Hmmm... this seems familiar somehow....

The range hoods actually work pretty well, as long as the fan is big enough to move all of the air. When attaching, make sure to fill the seams with epoxy or silicon compound to create a good seal. The inside install would be the most practical.
For ducting, just go to your local hardware store and pick up a dryer vent and elephant trunk. With that, you could just clamp the trunk on with ring clamps and not have to worry too much about the fit.

demono69