Venting the Garage/Fresh Air Intake
How are you guys venting your garage when painting bc/cc urethane?
I am thinking of raising the garage door enough to fit 3 or 4 fans next to each other along the floor, mounted into plywood that would seal from floor up to garage door and between the fans. At the back of the garage I can crack a door with a window open back there, so there would be a current moving through.
Are the dangerous fumes heavy, such that they will drop down to the floor level and get sucked out by the fans?
Is there concern the fans could create a spark and ignite the vapors?
Incase noone has any better ideas heres what i did when i used to paint in my garage. I had the garage cracked about 12 inches. THe back door i took a piece of plywood and cut two squares out and mounted two cheap box fans blowing outward. I then bought some filter material at homedepot and made a filter outside so the paint didnt blow out into my yard and over my lawn furniture. Worked good but I usually just did repairs like a side of a car or a hood with a blend. Since you are doing a whole car you might want to invest in some better fans. But it definately worked great this way you could see the overspray being sucked out. Goodluck
At least some of the fume components are indeed heavy and will tend to sink to floor level. Exhausting under a partially opened garage door will be effective, but will also exhaust the fumes at ground level where any person or animal walking by will get the full dose. While the fumes are flammable, you have to get in a relatively narrow range of concentrations to have an explosive mixture and given today's lower-VOC products this is highly unlikely to occur. Many, many people (including me) have used typical cheap box fans without problem. The primary hazard appears to be a build up of overspray on the fan motor leading to the fan motor overheating. I've heard tell of this leading to a fire on the fan motor, but have not experienced that. A relatively easy way to mitigate this problem is to place a filter (e.g. a furnace filter) on the garage side of the box fan to remove much of the overspray before it gets to the fan motor itself.
I encased my two car garage bay in plastic sheeting, hung from the ceiling with wood strips. Hung a filtered box fan (blowing in) from the ceiling on the end opposite of the door and duct taped it to an opening in the plastic. Put two filtered box fans (blowing out) under the door and sealed up the rest of the opening with plywood. Turned on all fans and used my electric leaf blower to remove as much dust as possible from the ceiling, floor and car (repeated 3x.) Wiped the car down 3x, let dry, paint. Also turned off the gas water heater prior to painting just in case.
Pat: I'm with you. I put 4 box fans under the small 8' door and put 2 20x 20 furnace filters on each one.Then I opened the double door about 6 in. and sprayed. Of course previous to this I washed the car with wax and grease remover twice blew the garage out with the leaf blower, tacked the car off and shot it. the fans sucked the overspray right out. I was very surprised at how fast the garage cleared out...I think you're on the right track....JMHO....GlennK
I was thinking of springing for one of these and pointing it outside, and maybe make a plenum for a couple furnace filters on the suction side of it...
I have an old furnace fan that moves alot of air. This summer I set up a negative pressure system, where I installed some heavy plastic over a doorway with staples & duct tape, and then cut a hole in the plastic to expose the intake of the blower. I mounted a pleated furnace filter in front of the intake, and had no issues with a cloud of overspray, or any paint on my driveway. I was painting black & yellow (GO STEELERS!:cool: ) I have since built a dog box to house the blower low and at the back of the garage for the exhaust, and have installed another furnace fan, for the supply, in the attic. Both are filtered, and the exhaust is ducted to a sump pit that is about 3' deep and normally has a few inches of water in to catch anything that may slip by. (I may also install a vent pipe from the sump pit about 8" high to exhaust the fumes?) With this setup, neither of the non-explosion proof motors are in the contaminated area, so I feel safe(er).
Thank you so much, everyone, for describing your set-ups. I wasn't sure if what I had in mind was crazy or not, but it sounds quite similar to what all you're doing.
I hadn't thought of using furnace filters in front of the fan to protect the motor from build-up. Very good idea.
Glad to hear the fumes are heavy; that'll work well with my fans at ground level. You make a good point about the exhaust being at ground level and affecting anyone around. We live away from any super-close neighbors, so no one will be walking around in the fumes, and I'll lock the dog and cats up in a room at the opposite end of the house...hopefully fumes won't reach there.
On that note, how far from the garage do the fumes generally travel (disregarding wind, etc.)? I'm wondering how long an intake for my fresh air hood I should have to get it sufficiently away from any bad air. Sounds like perhaps I should get the intake hose up higher-like in a tree branch-to further guard against nasty fumes, especially if they tend to be heavy. How long are your intake hoses on your fresh-air units, and do you put them up high?
Glenn-by 2 furnace filters on each fan, did you place both on the garage side/intake side, or did you do one on intake, one on exhaust? I assume that at the back of the garage where a fan pushes air into the garage it ought to be filtered on garage-side?
Great idea to use a leaf blower to blow out the garage first!
Pat: I taped two filters together and then taped them on the back side of the fans with the fans blowing out..I had no fans blowing air into the garage. The reason I used two on each fan was that one filter would not catch all the overspray and I would get a little in the motor ..with two filters the motor and the inside of the fan would stay clean....HTH...GlennK
As long as you're breathing fresh air it's not important to move the overspray out quickly. Moving a lot of air can cause the turbulence to pull dust from every nook and cranny onto the wet paint. However, if you're not using a supplied air breathing system it becomes more important to remove the overspray quickly.
If you don't have fast ventilation you want to be sure that you don't have a source of ignition in the room. It would be ashame to do all the work then get blown through the roof. Most of the new paints have little solvent so they aren't very explosive but a build up of a lot of dust in the air can be quite flammable and a little venting can help prevent building a hazardous condition. I don't want to scare you because you could have the overspray so thick you can't see across the room and not be in danger but it's good to have some venting to prevent this from happening.
Glenn-thanks for your clarification on how you place the filters. I'm glad you mentioned you don't bother with a fan blowing air INTO the garage, just several blowing out. I was just wondering last night whether I should be using an in-blowing fan in addition to all the exhaust fans. Guess it's not needed.
Len, I'm glad to hear the overspray does not have to be sucked out wicked fast, if using a fresh-air suit. I was imagining I needed some seriously fast-moving air to keep things reasonably safe. I'm glad this is not the case, especially with dust in mind.
I'll throw a few fans at the base of the garage door, cover them in 2 layers of filters to keep spray off the motors, and crack a door at the back of the garage, somehow filter it, use a fresh air system, and call it good.
Centrifugal fans (and pumps) in series (1 blowing OUT and another blowing IN) do not add flow, they change pressure. If you have access to 2 fans, just make them both blowing IN or both blowing OUT in parallel for maximum flow. This is my profession and thats how I'm going to do it, 2 blowing OUT in parallel. For the air coming IN, I do agree that a door or something to the garage be removed and furnace filters taped up there so the incoming air is clean.
Good luck with the garage paint-booths!
The main problem with a "negative" pressure set up is that it could suck trash from every nook & cranny of your booth/garage. And you can have other issues if you are hanging plastic. IMHO, I would create an exhaust vent, low, and have both fans blowing in from above to create a positive pressure atmosphere. But, it's been done "positive", "negative", and no ventilation at all. It's totally up to you.