Welding Fume Extractor:

I'm in the midst of building a new welding fume extractor setup - this will be vented via a 4" duct to outside. I'm having a HVAC sheetmetal place build a collector backstop that will vent out the top, go up, & through a blower, then make the turn & go outside. I need advice on what type of 4" blower (puller) to use. I obviously want all steel construction, but not sure about how many cfm would be best or what type. Anybody with any experience in this? Advice appreciated.

What are and how are you welding?

IMO, anything that moves any air will be a plus. In most cases you do not want an artificial breeze. Fortunately most of the fumes are hot, want to rise naturally, your goal it seems to me, is make the fumes move away from your face, and exhaust outside the building. On the choice of tube size, I would think the 4" might be on the small size.If you can incorporate an viable speed fan (DC?), you could really fine tune each application. I think a fume extractor is very smart.

the fume extractor over the welding bench at my former employment was HUGE !
the canopy covered the whole bench, and extended about 4" over the front and both sides.
the exhaust tubing was at least 8" or so, and when the fan was turned on, it really SUCKED ! [the FUMES that is. ]
this was before we got any mig welders, and after that, the fan was tamed down quite a bit so the suction didn't suck out the shielding gas. [we used straight CO2]
the drawback for not making the fan a two speed, was when stick welding heavy [thick] steel, the fumes took a lot longer to get sucked outside.
the vent was straight up through the roof, which was about 15ft or so.
this example might, or might not, apply to the OP. just an example of what i experienced at work for 42+ years.

MIG welding aluminized steel.

Grainger sells a wide variety of ventilators: wall/roof mounted, upblast or downblast, centrifugal or axial fan, direct drive/belt drive and a variety of duct sizes, horsepower, CFM, and voltage ratings.

Go to the website and search "wall ventilators" or "roof ventilators"

Yeah - I've looked at them. They'll make your head spin there's so many. That's why I was hoping someone that knows their stuff here can narrow it down for me. I doubt I'll find a fan expert if I call Grainger. They are jack of all trades, experts of none.

If you're venting to the outside then you need to draw fresh air in somewhere or the vacuum in the shop will eventually overpower the fan and nothing will move. Also, without drawing outside air the same vacuum will suck in any fumes/exhaust from any heat source - like a furnace, wood stove, etc.. Not good. And then, if you draw in outside air, you're going to freeze your ass off in winter.

A proper fume and smoke extractor will move a LOT of air. I have a standalone recirculating unit and it has an 8" diameter hose. The large hose actually serves to slow down the suction - enough to suck the smoke but not enough to suck away your sheilding gas. It has a large canister filter that has a flame retardant in case it sucks in sparks. I weld on average 15 hours a week and I wash the filter out annually.

My advice, if you haven't already blown a ton of money trying to reinvent the wheel ... invest in a recirculating unit and get on with it. You have to spend money to make money !! And yes, I know how much they are !!!

But if you must ... consider a bathroom fan or a range hood !!

I think SS mig welding might have the highest toxicity air borne. Your situation is on the smokey side, which is useful, in that at least you will see the effectiveness of your extractor solution.

I misspelled my first reply, I intended to mention "variable" speed.

Sorry, being from Florida, i didn't consider makeup air issues, you could if you wanted to get fancy, and save btu's in the winter, set up a two speed fan, that would trigger the higher fan speed off the welding arc. Not sure where your fan will be situated, but I hate constant fan noise, enough so on my Miller Synrowave 500 machine, I installed a low speed fan switch, and added some sound absorption material on the wall behind the machine, I like my hearing as much as my lungs.

I built this welding booth a couple of years ago. Should of built it decades earlier. I bought a variable speed Fantech (https://www.fantech.net/) exhaust fan. I picked one and called them for tech support. They were great and I ended up with the next larger size. I exhaust through a 6 inch pipe I used to use for an oil furnace that I don't use anymore. But honestly, it does not pull real hard. It does work, but I still wear a respirator whenever I weld. I'm anal.

I would call them, tell them what you want to do and get some feedback...........

A mask or respiratoris just common sense my friend. Regardless of how good the extractor is there are times you will forget to position it near your work or something. The mask should be your FIRST line of defense - the extractor is a convenience.

I welded and grinded (is that a word?!) for years with no mask and would blow black crud out my nose for days. I bought a decent 3M mask with pancake filters that fits under a helmet and Im regretting that I didn't do that when I first started welding. I occasionally weld stuff that's cadmium plated - not often and not much BUT the fumes are deadly. You want more than an extractor when you're doing stuff like that. 3M mask and 2097 filters. I change the filters after about 60 hours of welding.

http://www.effectivecontrolsinc.com/ for your fume extractor needs

www.airgas.com/product/Safety-Products/Respiratory-Protection/APR-Masks,-Cartridges-&-Filters/p/MILML00895 Miller weld mask for under your hood. Wish I would have had one over the years I welded stainless steel.

Link for you. I like it. I use a different style.

Respirator Link

Pretty neat stuff - also these extractor systems are VERY expensive! I'll post photos & share results with y'all after mine is set-up. I found an HVAC place that is going to build the vented weld station. I'm going to pick a blower/puller fan this weekend & order that. I made a trip to a local Grainger location earlier this week & they were of NO help at all. I knew more about it than the lady who "helped" me. I think this is going to work very well - if I get the right fan.

UPDATE - it's finished - just finished the run of ductwork to the trap door vent assy. outside. This is all 4". I had a local HVAC sheetmetal place build the box to my design - It's 38" long. I bought a Tjernlund blower - made in USA. Anyway, the flex section leading into the blower is OE grade 6-ply 304 stainless as used on truck exhausts (I had a piece of that laying around), the flex from the outlet of the blower to the 90* bend I bought at Lowes - it's HD flexible dryer vent hose - I needed something that could bend easily - it's actually plenty HD enough for this. The 4" tubing is 16-ga. aluminum mandrel-bent stuff from a local company that bends all kinds of tubing. All connections are screwed & sealed with aluminum tape. It works great. It'll pull in smoke from 3' away from the enclosure & send it outside. This is an updraft booth basically - I'm sure it will work well for doing small spray paint projects as well. Check it out:

Irs all based on face velocity. Depending on opening size to calculate the cfm of the fan. The bigger the opening the more cfm required. Research face velocity.

I THINK the answer is "whatever pulls the most CFM's." The size of your building (L, W, H) as well as where in that area the welding is taking place within that space all come into play. BUT, you said 4" outlet, so...something like this comes to mind:
https://www.amazon.com/VIVOSUN-Inli...&hvtargid=pla-314983957332&psc=1

A friend of mine uses a bathroom fart fan in a 18' X 24' shop with an 8' ceiling, placed over in the far corner, and it does OK, but I'd go with something better.

The blower I bought is rated at 200 cfm. Highest rating for any of the 4" ones I could find.

Unless that is an explosion proof fan motor, any spray paint is a no no, especially if that is a family dwelling.

Looks nice BTW.

The only comment I have is that for a 4" system like you have your hood may be too big for your fan. I'm guessing that fan is good for 100 cfm or so? And I'm guessing your hood is about 6' x 2'? You only have about 8 ft/min face velocity. That is really low. Typically the face velocity should be a minimum of 60 ft/min.

You can try what you have and if you are happy, you are the only one that needs to be satisfied. If it were me, I'd discard that hood and use something like this.

Welding Fume Nozzle

I'm not cheer-leading for this particular one, just the concept. We used this style at one of the power plants I worked at. We had a common large blower with a suction trunk that had individual drops for each welding table using hose and a bell style end with a magnet attachment. Worked for us. In fact, if a weldor got the hose to close to the work they complained it was like welding in a windstorm!

This is all correct. As an option he could add a curtain across the top or sides and minimize the size of the opening. This is how the fan should be sized using an engineered approach, without guessing. That 4" outlet , if too small can still be used by adding a higher static pressure rated fan. Look at the fan curve for static vs flow rate.

The width is 38", depth is 11", & height is 17", so it's not gigantic. Also, as said earlier the fan is rated at 200 cfm, not 100. I'll let y'all know once I get some welding underway - probably tomorrow.

I built a smoke extractor for my hydraulic hose saw on the cheap.
Was looking at extremely expensive options and consulted an associate with a much larger operation.
The pictures he sent appeared to be a purpose built extractor for industry.
He laughed and said nope, Harbor Freight.

What I used was the 660CFM 1HP DUST collector. Vented directly out of the shop. It works very well.

UPDATE: I finally did some welding this evening & this setup works better than I could have imagined. NO fumes, NO smoke. I even tried welding without a N95 mask (that's all I could fit under my welding helmet) - I don't need a dust mask anymore. The 4" system very adequately pulls everything out almost instantly - I'm loving the new setup!! VERY SATISFIED. I wish I would have done it years ago.

I'm glad it worked out for you. With your numbers you've got a face velocity around 45 ft/min which is respectable. I've always tried to weld outdoors or with the doors open as I just thought I couldn't afford a vent system. But your success is making me rethink this.

One more photo - the enclosure is behind what I'm welding, I don't weld inside of it. So it's pulling the fumes away from me & up & out.

Glad it works for you.

As I get older (wiser?) I find myself trying to be safer with stuff like that. Safety glasses, nitrile gloves, hearing protection, knee pads, etc. 20 year-old me would have not wanted to spend the extra few bucks on that type of thing, and would not have used it anyway....

Ain't it the truth.........