Spray booth exhaust

[Bryce Adams]

I'm going to set up a spray booth in my basement with poly sheeting hung from the ceiling. It will be near a window, and I'm thinking about an exhaust blower that I would set outside and run the flexible duct through the window.

This blower is rated 570 cfm. Does that seem reasonable to exhaust overspray? The next size up is 1650 cfm.

Thanks,

[Kevin Jenness]

A rule of thumb I have seen for spray booths is 100 linear ft./min. across the area of the empty booth. By that rule a 570 cfm (nominal) blower would adequately exhaust a 5.7 sq. ft. booth, a good size for turnings and the like. You can get by with less air flow than recommended but beware of flammable and toxic fume buildup, and make sure you have adequate makeup air. You should also consider how much air your blower can push through a flexible duct of a given area and length and what to use for filtration.

[Jim Becker]

Bryce, what you propose is good for waterborne finishes and Kevin's numbers seem reasonable. The point about make-up air is important; ideally, it comes from outside. The challenge for that is "where you live" and the seasons. If you live where there is winter, you'll be pumping your heat out and finishes are temperature sensitive. During the hot months, if your space is air conditioned, you'll be pumping cooler, drier air out and bringing hotter and potentially moisture air in. Keep all these things in mind as you decide how to set things up. Because I stick strictly to waterborne finishes (and occasionally a coat of shellac) for finishing, I don't vent outside. I use a larger air filter to collect the fines from the air, keep my spraying in one area, draping sometimes for containment, and wear PPE so I don't inhale those fines that get suspended in the air.

[John TenEyck]

I use a 1200 CFM blower to exhaust overspray (WB products) from my temporary spray booth, which has frontal area of about 6 x 8 ft. Not enough, technically, but it works.

John

[Andrew Seemann]

You will want to pay attention to the static pressure ratings in addition to the CFMs. Fans tend to be advertised at their CFM rating for free air, which is fine if it is going to be mounted in the wall with no restrictions. Once you start adding filters and ducts, it matters.

For example I sized my wall opening when I did my shop addition for a specific fan from Graingers. However, when I got around to buying it, I realized that the filters would add somewhere around .1 inch water column of static pressure. This dropped my fan's CFM rating in half, and not enough for what I needed. So now I need to get a different fan which a higher static pressure rating, which unfortunately requires an opening an inch larger. Argh

[Bryce Adams]

Thanks all for the advice. I'll just be spraying waterborne. Makeup air will be from an open window on the other side of the basement. I live in MN and hope the temperature drop in the winter won't be too bad for the amount of spraying I'll be doing. Probably won't add a filter. These blowers don't list a static pressure rating and they come with a 16' duct so it's hard to tell how much actual CFM they'll move.

[Jeff Monson]

Bryce, I have a very similar blower, slightly more cfm. It works pretty well and moves alot of air. You can always shorten up the tubing if needed. I'd highly recommend a filter of some type for your incoming air. A good quality furnace filter boxed into your booth will stop alot of fine material that will show up in your final finish. I prefer my exhaust and intake air to be low in the booth.

[John TenEyck]

I'll be the contrarion on this. You don't need or want filters in front of the blower. As long as the fan has 6 ft or so of duct between it and the booth. WB finishes will turn to powder before they get to the blower and be blown out the window. If you put a filter in front of the fan you will lose flow and it will blind over eventually. If you put it really close it will slag over and kill the flow much quicker.

If you want to spray solvent finishes you need explosion proof everything, and that's beyond my scope to offer advise except to say don't take chances.

[George Yetka]

I agree with John. Get an explosion proof fan. Vevor makes one. the 10" moves 3000 cfm. I would tend to think it is overrated

https://www.vevor.com/explosion-proof-fan-c_10372

[Bryce Adams]

It sounds like Jeff is suggesting a filter on the intake to the booth, not on the exhaust air. I'll have a 3-sided poly booth area, so there's no easy way to filter the intake air. Filters on the exhaust have the potential to cause the problems John mentions. I'm only setting up for waterborne, not solvent finishes.

[Kevin Jenness]

I'll be the contrarion on this. You don't need or want filters in front of the blower. As long as the fan has 6 ft or so of duct between it and the booth. WB finishes will turn to powder before they get to the blower and be blown out the window. If you put a filter in front of the fan you will lose flow and it will blind over eventually. If you put it really close it will slag over and kill the flow much quicker.

Do you really want to blow microplastics into the environment?

[Allan Dozier]

I have standard HVAC filters both for intake and exhaust in my finishing room. The filters on the exhaust get very full of overspray yet there is still some that gets through that show up on the outside of my building. I concede though that my fan is much stronger than what has been mentioned in this thread. By far most of what I spray is water based, usually Kem Aqua. If I didn't have the exhaust filters I fear my fan would be caked with paint. If your fan is low CFM you might get away with it I think.

[John TenEyck]

It sounds like Jeff is suggesting a filter on the intake to the booth, not on the exhaust air. I'll have a 3-sided poly booth area, so there's no easy way to filter the intake air. Filters on the exhaust have the potential to cause the problems John mentions. I'm only setting up for waterborne, not solvent finishes.

Oh, perhaps I misread Jeff's post. Air filters on the intake would be helpful if you have a sealed spray booth and a dusty shop. I haven't found them necessary with the WB finishes I use. I have a setup very much like Jeff proposed. Plastic draped from the floor joists, an open front at the front or the booth, and an open window across the room for makeup air. I vacuum the floor before I set up the spray booth, nothing more. I've never had problems with dust, etc settling in the finish. The bigger problem has been stuff falling off me into the wet finish, to the point that I make sure I'm wearing a clean shirt and have nothing on my arms or face or in what little hair I still have.

John

[John TenEyck]

Do you really want to blow microplastics into the environment?

Whatever little amount of microplastics I'm blowing outside land in my landscaping and grass. I'm nowhere near a waterway. I honestly don't see an issue.

John