Finish room venting question

[Phil S]

As I am getting ready to frame the floor system for my new shop, I am thinking about running vent lines before I install the subfloor. I am planning on blowing air into the room pushing the vapors out the vent. That way the flammable vapors will not be pulled through a vent fan possibly causing a fire.
My questions are how much cfm do I need for an 8x8x8 room and how big of a vent pipe do I need.
Also since I think the vapors are heavier than air, I am guessing that I should blow the incoming air in at ceiling height and the outgoing vent should be at floor level.
Please correct me if I have that backwards
Thanks and stay safe during this storm

 

[junquecol]

Phil, drop in at Agri-Supply and look at their grain dryer vent fans. Remember that grain dust is highly explosive. I know several who use them on their spray booths

 

[FredP]

I would pull the fumes out with an explosion proof fan. The reason is when you pressurize [positive pressure system] a room to force the fumes out they will leave by whatever exit is available. IE; If you open the door to the shop the fumes will enter the shop. If your door to the shop is not fully sealed [they rarely are] fumes will enter the shop. If there are any ways for the fumes to enter the house they will find those as well. with a negative pressure system if you open a door ect... the fumes are still being sucked out through the fan.

 

[Bill Clemmons]

Phil, the system you are describing is called "positive pressure", as opposed to "negative pressure", where air is sucked out of the room. When I built my shop I did a modest amount of research and used this approach for my finish room.

From everything I read, it said to put the input air at the bottom of a wall on one side of the room, and the outlet vent either in the ceiling or high on the wall opposite the inlet air. I don't know if that is technically correct, but it's what I read from several sources, so I did it that way.

My finish room is 12x12 w/ a 10' ceiling, which gives me 1,440 cu. ft. of air. W/ a 300 CFM fan I'm theoretically exchanging the entire volume in just under 5 minutes. It works okay, but if I had it to do over again, I would go w/ a 500 - 700 CFM fan, just to give it a little more push.

The exhaust vent is a 8" dia. piece of HVAC duct that goes up through the roof. I think that is adequate. It's located in the center of the ceiling, but in hindsight it should be in the corner opposite the inlet fan.

To prevent the loss of heated or cooled air when the room is not in use, I rigged a sliding door to cover the exhaust vent. It's just a 1" piece of Styrofoam insulation glued to a piece of 1/4" plywood, and slides in a simple track to open or close.

The infeed air needs to be filtered BEFORE it enters the fan. Otherwise, you will suck dust from the rest of the shop into your finish room. I use a double filter system, and change them often.

Once I'm in the finish room and close the door, it is almost air tight. Every seam, from floor to ceiling, is caulked and sealed. The only air coming in or going out is that being pushed by the fan. Otherwise, the pressure from your inlet fan will push vapors (especially when spraying) out into your shop, as well as through the exhaust vent.

Finally, put your control switches for the fan and lights OUTSIDE the finish room, not inside. That way, when you open the door to leave the room after applying a finish, the fan is still running and pushing the vapors out w/ you, instead of allowing dust from the shop to come into the room and settle on your wet project.

If you happen to find yourself anywhere near the Triad area, you are more than welcome to come by the shop and see what I've got. I'll be glad to show you the mistakes I made. :wwink:

Bill

 

[FredP]

What bill says makes good sense from a finish standpoint. I am wondering if a 3 way switch would make sense. One outside the room and one inside the room might be helpful. turn it off when you enter or leave the room and back on after the door is shut. no air movement means no fumes or dust moving=better finish and better air quality. I spray a lot of lacquer. Those fumes are well.... you know.:icon_thum

 

[Phil S]

What bill says makes good sense from a finish standpoint. I am wondering if a 3 way switch would make sense. One outside the room and one inside the room might be helpful. turn it off when you enter or leave the room and back on after the door is shut. no air movement means no fumes or dust moving=better finish and better air quality. I spray a lot of lacquer. Those fumes are well.... you know.:icon_thum

Fred, I think you have a great suggestion here. Should improve both a positive or a negative pressure design thanks

 

[Bill Clemmons]

What bill says makes good sense from a finish standpoint. I am wondering if a 3 way switch would make sense. One outside the room and one inside the room might be helpful. turn it off when you enter or leave the room and back on after the door is shut. no air movement means no fumes or dust moving=better finish and better air quality. I spray a lot of lacquer. Those fumes are well.... you know.:icon_thum

The main reason I put my switches outside the finish room was to avoid having to use an explosion proof switch. I don't know if this is absolutely necessary, or just overly cautious, but the reading I did suggested it. Theoretically, a spark from a standard switch could cause an explosion, especially if you're spraying something volatile. Like you, I spray a fair amount of lacquer, plus oil based varnish and shellac.

Fred, there was another point you mentioned in your first post that just caught my attention. You're absolutely right about the room needing to be sealed to avoid fumes getting back into the shop. The first time I sprayed shellac, I was surprised when I opened the door and saw the cloud in my shop. That's when I got out the caulk gun and went to work. I'd guesstimate it's probably 95+% air tight now, and that eliminated the problem.

The other thing is opening the door and having all the fumes blow out into the shop. After I finish spraying, I empty the cup on the spray gun, then spray a few ounces of solvent through it to clean it out. By the time I get around to opening the door to leave, probably 5-7 minutes have elapsed, and the fumes are all gone. Probably if I opened the door while the fumes were still hanging around, they would blow out into the shop. I guess being old and slow has it's advantages. :wink_smil

One more point I was thinking of. When I open the door to leave the finish room, the fan is still running. That means air is blowing OUT of the finish room. If air was being pulled INTO the finish room, I'm afraid it would pull dust from the shop across my wet piece and make one heck of a mess. That's one of the main reason I went w/ the positive vs negative system. That plus the need for explosion proof fan and switches.

I don't know if my way is the right way (probably not since I rarely seem to do anything the right way) but it works for me. :gar-Bi

Bill

 

[FredP]

The main reason I put my switches outside the finish room was to avoid having to use an explosion proof switch. I don't know if this is absolutely necessary, or just overly cautious, but the reading I did suggested it. Theoretically, a spark from a standard switch could cause an explosion, especially if you're spraying something volatile. Like you, I spray a fair amount of lacquer, plus oil based varnish and shellac.

Fred, there was another point you mentioned in your first post that just caught my attention. You're absolutely right about the room needing to be sealed to avoid fumes getting back into the shop. The first time I sprayed shellac, I was surprised when I opened the door and saw the cloud in my shop. That's when I got out the caulk gun and went to work. I'd guesstimate it's probably 95+% air tight now, and that eliminated the problem.

The other thing is opening the door and having all the fumes blow out into the shop. After I finish spraying, I empty the cup on the spray gun, then spray a few ounces of solvent through it to clean it out. By the time I get around to opening the door to leave, probably 5-7 minutes have elapsed, and the fumes are all gone. Probably if I opened the door while the fumes were still hanging around, they would blow out into the shop. I guess being old and slow has it's advantages. :wink_smil

One more point I was thinking of. When I open the door to leave the finish room, the fan is still running. That means air is blowing OUT of the finish room. If air was being pulled INTO the finish room, I'm afraid it would pull dust from the shop across my wet piece and make one heck of a mess. That's one of the main reason I went w/ the positive vs negative system. That plus the need for explosion proof fan and switches.

I don't know if my way is the right way (probably not since I rarely seem to do anything the right way) but it works for me. :gar-Bi

Bill

I'm not sure there is a right or wrong way.:gar-Bi Both methods have thier own set of uhoh's. E/P fans are not cheap but E/P switches aren't that much. You prolly wont find them at slows or home cheapo but an electrical supply house would carry them. I believe hospital grade switches are E/P. [don't quote me on that though]:gar-Bi

 

[Randall Kepley]

Bill, would you mind posting some pix of your set up? Thanks R.K.

 

[Bill Clemmons]

Bill, would you mind posting some pix of your set up? Thanks R.K.

I'll try to remember to take some pics tomorrow, and post them tomorrow night. This one shows the doors going into the finish room. The fan w/ filters is at the bottom of the pic, beside the trash can. I've since redone the box it's in to make it easier to change the filters. You'll see that in the pics tomorrow night.

Is there anything specific you want to see? If so, I'll make sure to take extra pics of it.

View image in gallery​

Bill

 

[Bill Clemmons]

RK, I took a bunch of pics of the finish room today, but due to the photo upload problem we're experiencing, I can't get them loaded onto the site. As soon as the problem is resolved, I'll upload them and provide a link to the album.

Bill

 

[Randall Kepley]

Looking forward to seeing the, thanks a lot Bill. R.K.

 

[Bill Clemmons]

Looking forward to seeing the, thanks a lot Bill. R.K.

I haven't forgotten about it. I just tried to upload the photos again and still getting the Upload Error 500 message. As soon as the staff let's us know it's fixed I'll get them posted. :thumbs_up

Bill

 

[Bill Clemmons]

Bill, would you mind posting some pix of your set up? Thanks R.K.

Better late than never. :gar-Bi There are a bunch of finish room pics here. If something doesn't make sense, please don't hesitate to ask about it. This is the fan and filters outside the room, w/ the lid removed.

View image in gallery​

Bill

 

[Randall Kepley]

Thanks for all the pix Bill, very detailed as I was sure they would be. R.K.