exhaust fan question

[Mark Boyette]

I'm looking to purchase an exhaust fan for my shop and curious the thoughts from those here. It's mainly to exhaust fumes from staining and small spraying projects. One of our venders at work has a sale on a shutter style. They have a 24",20, 18", and 16" models. I was looking at the 18" 3 speed unit. The CFM's for 4750 on high, 3800 on medium, and 3150 on low. Would mount on a side wall.
The shop is 1,200 square feet with 10' ceiling but the back portion of the shop where the fan is going to be has 8' ceilings.
Would this size be suffcient? Also what's the best way to get the make up air in? just open a window or crack the overhead door? Curious how it might work out in the winter when the furnace is on.
thanks for any insight.
Mark.

[Greg Pierce]

Mark,
I learned a lot about the exhaust fans when building greenhouses. One thing that I didn't realize was that having a door wide open is not better than just a crack in it, or depending on how much cfm the fan is pulling, no crack at all if your building is loose. They tell me if you have the door wide open, the air doesn't move very fast through the shop, or greenhouse. You have to match the intake to the output.

Maybe this helps, somewhat, good luck on your shop.

[Harold Shay]

Mark,
I don't want to sound stupid but if you are going to use the fan while spraying you will want to make sure it is one that does not create sparks while running. It has been by experience that fumes are what is flamable and not the acutal liquid. Your shop will have to have a fresh air inlet to let the exhaust work proper. So what ever you decide on the fan you will need to let that much fresh air in.
Harold

[David Christopher]

Mark, I have a 16" attic fan installed in the top, back of my shop..to work correctly I close the doors and open one window and then it will remove all dust, fumes or smoke in just a few seconds but if I open the door it dont do a very good job.....as mentioned above you need about the same opening as the fan......the only bad part is all heat or AC will be removed in seconds also......great in spring or fall

[Mark Boyette]

thanks guys.. that's pretty much what I was thinking.
I appreciate the responses.
Mark.

[Matt Meiser]

Bigger=Better. On mine, I open a window usually. But if the door isn't latched completely it will suck the door right open.

[Mark Boyette]

Bigger=Better. On mine, I open a window usually. But if the door isn't latched completely it will suck the door right open.

thanks matt.. what size cfm unit are you running?
Mark.

[Matt Meiser]

4295 CFM This is the fan I have: http://www.grainger.com/Grainger/items/3XK57

But I didn't pay anywhere close to that. I bought it off Ebay about 4 years ago and paid $100 including shipping! It had only been used for certification testing and looked like new. The price has really gone up--at the time they were only around $300 new. Same for the louvers. I paid $30 for them from Grainger and now they are close to $70.

[Rob Russell]

Mark,

Be careful about using the fan in the winter if your furnace is running. That strong a fan will suck all of the furnace exhaust right back into your shop and you don't want to be breathing that carbon monoxide and other good stuff.

Rob

[Mark Boyette]

Rob,
Good point.. I'll make sure to shut the furnace down when I'm running it.
thanks!
Mark.

[Matt Meiser]

Oh, yes--that happens to me, not the CO poisoning, but it causes my furnace to shut down if the door or window isn't open because mine has a sensor to detect proper draft. If I open a window, its fine since the fan draws from the path of least resistance, but I shut off the furnace anyway while the fan is running because its just sucking the heat right out.

[Damon Marxer]

I am in the midst of building a 24 x 36 shop and had done some research on this a few months ago. I ended up buying an 18" fan from Global Industries. It sounds similar to the one you are describing and I know they have other sizes. They seemed to have the best price that I could find. Here is the link.

http://www.globalindustrial.com/gcs/prod/30018174/i/productInfo.web

Hopefully this helps.

Damon

[Scott T Smith]

Mark, rather than using a higher CFM fan and exchanging the entire shop air, is it an option for you to build a paint booth along one wall (or use drop-down curtains) and use a low CFM fan to just remove the paint fumes?

That would solve the problem with losing your conditioned air, sucking air from the furnace, etc, not to mention controlling overspray.

[Matt Meiser]

When I was building a spray area, I remember seeing recommendations for minimum velocity across the face of the booth. If you move 4000 cubic feet/minute and have a 7x7 (49 sq.ft) opening you get a velocity of about 81 ft/minute or 1.3 ft/s. If I remember correctly, that's on the low side of the recommendation. But, it works well for me. I wouldn't want less air movement. Plus when I'm spraying something too big to fit in my "booth" there's a lot less movement than that.

The other general advantage of a big fan is you can use it in general to exhaust air from your shop and suck in fresh air from outside. I haven't done it when woodworking, though I should. But it works incredibly well to clear fumes when welding.

[Mark Boyette]

Damon... I think that is the exact same unit I have on order. How has it worked for you? I thought it would be nice to have the 3 speeds.
I have a full spray booth at work that I'm able to use so mainly smaller spray projects at my place. I thought about enclosing a area but until I need to spray more I'll keep it open.
Thanks for all the input.. good advice as usual.
Mark.

[Damon Marxer]

Mark: I cannot say how it has worked out yet as I am still completing my shop. I have been building it all summer long and I am getting close to being complete. I had done a bunch of research on the woodworking forums and asked a lot of questions at our local woodworking group forum and that is what convinced me to get an exhaust fan.

What I am going to do is build a tunnel that goes through my utility room for the DC and Air compressor that is up high. This will keep the noise of the fan down in the shop and then I will stack some furnace filters on the inside wall to prevent dust and fumes from getting into the motor.

I will take pictures once the fan is complete that you can see at this link.

http://picasaweb.google.com/DamonsWoodworking/OutbuildingConstruction#

[Matt Meiser]

Damon, I have 4 20x25 filters in frame so they are 2 high and 2 wide. After a few uses they get so plugged you can notice the difference in airflow and actually see the filters getting sucked in. I really need to get a manometer to measure the drop in pressure across them like a real spray booth but haven't. But my point is moving that much air, make sure you have a lot of filter area otherwise you'll choke your fan.

[Mark Boyette]

very nice... I went throught that last summer with my new shop. Love the shop but didn't get the boat out much that year.
yours looks great so far.
Mark.



Mark: I cannot say how it has worked out yet as I am still completing my shop. I have been building it all summer long and I am getting close to being complete. I had done a bunch of research on the woodworking forums and asked a lot of questions at our local woodworking group forum and that is what convinced me to get an exhaust fan.

What I am going to do is build a tunnel that goes through my utility room for the DC and Air compressor that is up high. This will keep the noise of the fan down in the shop and then I will stack some furnace filters on the inside wall to prevent dust and fumes from getting into the motor.

I will take pictures once the fan is complete that you can see at this link.

http://picasaweb.google.com/DamonsWoodworking/OutbuildingConstruction#