Exhaust fan for attic - Contractor Talk - Professional Construction and Remodeling Forum

Handyman · 06-22-2007, 02:45 PM

A friend of mine has a 4 car garage that he does body work out of. He mostly does race cars. He currently has a attic ventalation fan on one side of the garage. Actually the fan is located inbetween both sides, but at one end opposite the garage doors in the area where he does the painting. The exhaust fan is boxed up through the attic to the roof. The problem is there seems to be a backflow draft coming back down the fan. When he takes the cap off to totally expose the opening of the box of air flow it seem to stop some. But there's still a backflow draft. The boxin is a little smaller the the fan size, but not by much. I mentioned to him to move the exhaust fan to the middle at where he paints to get the full effect of the exhaust fan.

My question is: Is there a better way to do this? With keeping the expenses down. Or is there something that can be done to better what he's currently using.

MSSI · 06-23-2007, 05:25 PM

the expensive route..............
http://www.wholehousefan.com/?gclid=...FQqtOAodHDfBDw

MSSI · 06-23-2007, 05:31 PM

The cheaper route..or he could fabricate something like this...
http://heating-and-cooling.hardwares...ELAID=42539782

mdshunk · 06-23-2007, 08:19 PM

Are you saying that he paints cars in a location where he uses a regular whole house fan? You might want to post his address so I'll know where to send the sympathy card to the family when he has a flash fire in his garage.

Handyman · 06-24-2007, 09:57 PM

What he's using is doing the trick. But, It has it's problems. He's been doing this for a few years now. He opens the windows and the garage door. Nothing gets ventilated to the house. Nor the upstairs area. It get's ventilated out. When I seen it I was asking for anyone else's input to help correct his current hookup. So, unless you have anything worth the energy to type, just sit back and relax and wait for someone that knows what they're talking about or has some input to help with my original post. =) Maybe you could learn something as well =))) There are obvious answers and there are ones that will move things in a more positive direction. Like the two post replies before your nonsense

mdshunk · 06-24-2007, 10:01 PM

Quote:

Originally Posted by Handyman

What he's using is doing the trick. But, It has it's problems. He's been doing this for a few years now. He opens the windows and the garage door. Nothing gets ventilated to the house. Nor the upstairs area. It get's ventilated out. When I seen it I was asking for anyone else's input to help correct his current hookup. So, unless you have anything worth the energy to type, just sit back and relax and wait for someone that knows what they're talking about or has some input to help with my original post. =) Maybe you could learn something as well =))) There are obvious answers and there are ones that will move things in a more positive direction. Like the two post replies before your nonsense

I wouldn't have even had to know your handle to know you were a handyman, just from reading that response. What this guy is doing is industrial strength stupid.

Handyman · 06-24-2007, 10:14 PM

Do you actually read what you write? I didn't say I did it, I asked if anyone had any Ideas to better it or do it better. Didn't say it was a commercial garage. It's just something he does out of his house. Just trying to take something and do it right or make things better for him.

Just because I picked a name like I did doesn't exactly mean I'm a handyman. Just means it's the name I picked. As for my post it was a genuinely good question. And besides My original post was if you can read right was

"My question is: Is there a better way to do this? With keeping the expenses down. Or is there something that can be done to better what he's currently using."

As for Stupidity. Is it your self confidence that makes you feel that way or is it just your inner natural response? Try, just try a little to think before you speak. Because it seams you're not comprehending the words you're reading on my original post. So, stop hurting yourself.

So, again, if you have something to add besides ignorance please feel free to do so.

LNG24 · 06-24-2007, 11:02 PM

Let me try to throw some water on this fire. If this is your friend, you really want to research the correct way to exhaust the Paint Fumes the same as any commercial garage would do. The reason is simple. Dosn't matter if you spray once a year or once a day. Paint Fumes are VERY VERY flamable. A Flach Fire will occure if anything causes a spark and the air mixture plus paint spray is correct. This could be a simple breaker tripping, the spark from an outlet as something is plugged in or out or THE EXHAUST FAN ITSELF. From what I recal the exhaust fan motor is kept outside of the chanmer so it can never mix witht he fumes.

He would be doing his family wonders if he simply invests in a REAL Exhaust fan for spray painting.

gregj · 06-25-2007, 10:23 AM

MD and Digger are giving you very good information. I hope you consider it carefully.

Tmrrptr · 06-25-2007, 01:04 PM

If numbers will help avoid a big bang, I'll weigh in...

Flash point of lacquer is VERY sensitive.
Other solvents also have low flashpoint.

The wrong fan can make a big boom 1st time switched on,
or any other time, if it didn't before.

Better to be cautious than lose a home.
r

SmithBuilt · 06-25-2007, 06:28 PM

Is the fan motor totally enclosed? If not you would have armature brushes that constantly spark and could cause an explosion.

**Leo G** · 06-25-2007, 07:14 PM

Although these guys are looking out for your safety, and I do agree with them. Getting an explosion or a flame up is not very likely if you have airflow before you start spraying the paint. But this is the wrong way to think about it. If you were to set up a proper fan system with the proper exhaust baffle and filtration and have 100 lineal feet of airflow per minute, This would not be a problem. The proper setup would be an explosion proof fan with a motor that is not in the fume stream and have a non-sparking fan blade (aluminum). This should have a paint catching filtration system before the fan to catch the solids so they don't deposit on the fan blade and housing so that a future fire cannot occur. If he is having backflow issues with the fan then the airflow path is wrong and needs to be adjusted. The fan should be unobstructed 2 fan diameters behind and 1 fan diameter ahead of the fan. If this is not the case then this setup is wrong and inadequate. A three car garage is a large area and the CFM required from your fan would be very large. I doubt the fan is strong enough to supply the needed air movements to have a safe environment to work in. I have a spraybooth that I assembled and it has a cross sectional area of 162 sq ft which make my fan requirements quite large. The 100 lf of airflow means I need a fan that pulls 16,200 CFM, it is a 36" 3 HP explosion proof setup. To have the airflow in your friends garage would require an immense fan. He should have a much smaller blocked off area that would be the area the fan in restricted to. Safety first saves lives.

MSSI · 06-26-2007, 04:29 PM

Quote:

Originally Posted by MSSI

the expensive route..............
http://www.wholehousefan.com/?gclid=...FQqtOAodHDfBDw

All I saw was ...Shop and body work.....I really didnt read the painting part, that was mentioned, I would have tried to steer in a different direction....

We are all Pros here right? Do we really need to state the obvious?

I guess I just assumed Haz-loc equipment was already considered and deemed not necessary, I guess I got this thread confused with "contractor" talk instead of DIY

Handyman · 07-01-2007, 10:19 PM

I appreciate the advice that was given. I knew the obvious I was just looking for some insight on the not so obvious from people that know what they are talking about. I know and am familiar with the basics but wanted so input from others that were fairly knowledgeable in this area. My friend was okay with the way he had things. I wasn't which is why I was looking for more information. Again, thanks for the input that was given to help me in the right direction.

dlcj · 10-21-2007, 05:43 PM

Hey handyman. If you are still reading this tread, this is what my dad done in his shop. We built a portable paint booth. Using 2x2s as a frame and stapling 6 mill clear plastic over them. we have 10- 7'x14' sections that we screw together making a 28x14x7 plastic box, when he is ready to paint. One end section has 2- 24" ac filters and the other end has the door and one box fan ($12 at walmart).The fan blows out the shop door. It works great and no dust gets in. The booth is that big cuz the first thing he used it for was my full size crew cab truck. Total cost $100. The fan is all plastic but we did not give a thought about the brush sparks. We may have to come up with a venturi style duct using the same fan and some more plastic.

**Leo G** · 10-21-2007, 05:45 PM

Quote:

Originally Posted by dlcj

Hey handyman. If you are still reading this tread, this is what my dad done in his shop. We built a portable paint booth. Using 2x2s as a frame and stapling 6 mill clear plastic over them. we have 10- 7'x14' sections that we screw together making a 28x14x7 plastic box, when he is ready to paint. One end section has 2- 24" ac filters and the other end has the door and one box fan ($12 at walmart).The fan blows out the shop door. It works great and no dust gets in. The booth is that big cuz the first thing he used it for was my full size crew cab truck. Total cost $100. The fan is all plastic but we did not give a thought about the brush sparks. We may have to come up with a venturi style duct using the same fan and some more plastic.

Can you say BOOM?

dlcj · 10-21-2007, 05:53 PM

Quote:

Originally Posted by Leo G

Can you say BOOM?

He has painted about 8 cars and no boom but i see the danger now and we will build that venturi before the next job. Not everyone can afford the best so we have to have ingenuity to make up for the lack of money.

**Leo G** · 10-21-2007, 06:00 PM

Quote:

Originally Posted by dlcj

He has painted about 8 cars and no boom but i see the danger now and we will build that venturi before the next job. Not everyone can afford the best so we have to have ingenuity to make up for the lack of money.

If you want to use the same setup and be safer you can use the fan to push air into the area instead of suck it out. That way the only thing that is going through the fan is fresh air. It is called a positive pressure spray room. When you have the air sucked out it is a negative pressure spray room. Just because it hasn't happened doesn't mean it won't. Spend some money, be safe, stay alive. That is all I hope for.

dlcj · 10-21-2007, 06:20 PM

Quote:

Originally Posted by Leo G

If you want to use the same setup and be safer you can use the fan to push air into the area instead of suck it out. That way the only thing that is going through the fan is fresh air. It is called a positive pressure spray room. When you have the air sucked out it is a negative pressure spray room. Just because it hasn't happened doesn't mean it won't. Spend some money, be safe, stay alive. That is all I hope for.

we can prolly do that and ad another fan for more pressure. (12 more dollars, damn!)

Thanks, but i hope we helped trendstarter too.

**Leo G** · 10-21-2007, 06:25 PM

Quote:

Originally Posted by dlcj

we can prolly do that and ad another fan for more pressure. (12 more dollars, damn!)

I made my own spray room. It cost $7900 for materials alone. Myself and a buddy put in 120 hours each to construct it. I have a 3HP 36" fan and operate a negative pressure room. I have 8 input filters and 54 sq ft of exhaust filter. I need to get more input filter area. The fan pulls about 17,000 cfm. Worth every penny.