Spray room ventilation

[iublue]

My spray room is approximately 10 1/2' x 7' x 9'.  I spray exclusively waterborne finishes so I see no need to exhaust to the outside.  I just need to be able to get filtered air into the room and also filter the air as it leaves the room.  Approximately 660 cubic feet of air in the room.

What kind of fan do people use?  I wondered about the fan mentioned in the air cleaner thread but I don't know how many CFM's I really need.  I would think exchanging the air volume every 30 - 60 seconds would work or am I wrong??!!

[jteneyck]

My spray room is approximately 10 1/2' x 7' x 9'.  I spray exclusively waterborne finishes so I see no need to exhaust to the outside.  I just need to be able to get filtered air into the room and also filter the air as it leaves the room.  Approximately 660 cubic feet of air in the room.

What kind of fan do people use?  I wondered about the fan mentioned in the air cleaner thread but I don't know how many CFM's I really need.  I would think exchanging the air volume every 30 - 60 seconds would work or am I wrong??!!

If your spray booth is near any living quarters then you definitely do want to exhaust the air outside.  Even WB's have some things you don't want to breathe.  And many WB's conversion varnishes have some really nasty stuff in them; for those you also wanted to be suited up.  None of them can be easily filtered.  

It's not so much the number of air exchanges per unit time that's important as it is velocity over the work to carry away the overspray.  Commercial booths usually have around 100 fpm "face velocity" but you can get by with half of that, maybe even less if you always spray front to back, towards the exhaust inlet.   I get by with a 1200 CFM DC fan in my spray booth with a frontal area of about 56 sq ft., so that's only 20 fpm face velocity.  It works fine with the shellac and WB's I use.  

John

[iublue]

If your spray booth is near any living quarters then you definitely do want to exhaust the air outside.  Even WB's have some things you don't want to breathe.  And many WB's conversion varnishes have some really nasty stuff in them; for those you also wanted to be suited up.  None of them can be easily filtered.  

It's not so much the number of air exchanges per unit time that's important as it is velocity over the work to carry away the overspray.  Commercial booths usually have around 100 fpm "face velocity" but you can get by with half of that, maybe even less if you always spray front to back, towards the exhaust inlet.   I get by with a 1200 CFM DC fan in my spray booth with a frontal area of about 56 sq ft., so that's only 20 fpm face velocity.  It works fine with the shellac and WB's I use.  

John

Thanks for the reply John.

The shop is stand alone so no living quarters issue.  I never spray conversion varnishes.  About all I spray is General Finishes Enduro.  When I sprayed in my old shop, unless something was immediately behind the direction I was spraying, everything else was just covered in dust from the dry over-spray.

How do you make up the exhausted air?  My new shop building has no windows and no outside opening in the spray room.  It has one overhead garage door and one 3' entry door.  I guess I could cut an opening in the spray room but I would rather not do that.

Toney

[jteneyck]

Thanks for the reply John.

The shop is stand alone so no living quarters issue.  I never spray conversion varnishes.  About all I spray is General Finishes Enduro.  When I sprayed in my old shop, unless something was immediately behind the direction I was spraying, everything else was just covered in dust from the dry over-spray.

How do you make up the exhausted air?  My new shop building has no windows and no outside opening in the spray room.  It has one overhead garage door and one 3' entry door.  I guess I could cut an opening in the spray room but I would rather not do that.

Toney

I open a window at the other side of my shop for makeup air.  I don't filter the air going into or out of the spray booth and have no problem with dust getting onto my freshly sprayed surfaces.  If you exhaust outside there's no reason to filter the exhaust and plenty of reasons not to.  In your case, you could leave the garage door open a couple of inches for your makeup air. 

If you want to create a system like you originally proposed, you are going to have to filter the outlet air to stop the over-spray from getting spread around your shop.  I would consider a baffle system that the air has to travel through before reaching the fan.  (A low cost box fan will work fine for the size of your booth.)  Any wet overspray will stick to the baffles and the dry overspray will fall to the floor if you let the air decelerate enough before it reaches the fan.  And if some reaches and sticks to the fan it's no big deal.  You can replace it in a few years at low cost if that happens.  You can filter the incoming air if you want.  I'd make the inlet opening at least 2X the size of the outlet fan discharge opening.

[iublue]

I open a window at the other side of my shop for makeup air.  I don't filter the air going into or out of the spray booth and have no problem with dust getting onto my freshly sprayed surfaces.  If you exhaust outside there's no reason to filter the exhaust and plenty of reasons not to.  In your case, you could leave the garage door open a couple of inches for your makeup air. 

If you want to create a system like you originally proposed, you are going to have to filter the outlet air to stop the over-spray from getting spread around your shop.  I would consider a baffle system that the air has to travel through before reaching the fan.  (A low cost box fan will work fine for the size of your booth.)  Any wet overspray will stick to the baffles and the dry overspray will fall to the floor if you let the air decelerate enough before it reaches the fan.  And if some reaches and sticks to the fan it's no big deal.  You can replace it in a few years at low cost if that happens.  You can filter the incoming air if you want.  I'd make the inlet opening at least 2X the size of the outlet fan discharge opening.

Thanks

[Stwood_]

Mine was 16x16 and I bought a fan with the louvered cover on it from Grainger, and installed it in an outside wall.
I never got a filter assembly in the door to let air in. I just left the door cracked open.

[Woodshop]

I built a spray room put a 36" fan in wall with outside louvered and put filters in front to save the fan. all that cost was NOT worth it . very pore job of clearing the air, clogged filters fast, pulling the cool/warm air out of the shop.
I built a 16x16 lean-to out the back of the shop where I had double doors and spray there, carry out spray carry in. life is good.  only days I can't spray is blowing rain days. I mainly spray oil base polly.
seriously the ex-host fan it's not worth it. in my opinion

[jteneyck]

I built a spray room put a 36" fan in wall with outside louvered and put filters in front to save the fan. all that cost was NOT worth it . very pore job of clearing the air, clogged filters fast, pulling the cool/warm air out of the shop.
I built a 16x16 lean-to out the back of the shop where I had double doors and spray there, carry out spray carry in. life is good.  only days I can't spray is blowing rain days. I mainly spray oil base polly.
seriously the ex-host fan it's not worth it. in my opinion

Oil based products are the worst with respect to filtration.  In a typical arrangement, the overspray won't dry before hitting the filter, as you found out, and will quickly coat it and render the exhaust fan ineffective.  The only way to deal with it is to install a tortuous path for the exhaust air so that the particles slag up something else, before they hit the filter.  An undersized fan will help, too, as you want the overspray to fall out before getting to the filter.  All you want from the fan is to move the overspray away from what you just sprayed.  I get a lot of dry powder from the WB products I spray on the floor at the back of my booth, which gets wrapped up in the cheap painter's cloth I put on the floor, and then tossed in the trash.  

A commercial solution is overly expensive and unnecessary for the home shop, as long as you don't spray solvent based products.  

John