Fume Extractor for Under \$20 - Page 2

# Thread: Fume Extractor for Under \$20

1. Solderer
Join Date
Feb 2017
Posts
8

## Re: Fume Extractor for Under \$20

Short Explanation:

I do this kind of thing for a living. And yes, it can be a bit pricey for the home hobbyist. If I was to DIY, I would pay attention to the following.

Generally you want to shoot for volume of air. I recommend 1,200 CFM, but many people go with 800 CFM.

There are a few things you need to consider for this system. I am going to assume this is to exhaust, and not filter the fumes.

Fume Arm (or snorkel, or whatever you want to call it).

Recommend some kind of rigid setup so it stays in position and does not flop around. If impractical, flex hose will do, but make sure you have a way to keep it in position so it is effective.

Go with 6" or 8" diameter.

With the right fan, arm diameter will do the following:

6" = 800 CFM
8" = 1,200 CFM

I'll get into this a little bit further when I talk about fans, but basically you have a limit of how much volume of air you can pull through a certain sized arm. Pull air through a regular straw, and then try to pull the same volume of air through a coffee straw. It is not possible, the coffee straw would collapse before it was possible. Like I said, we are just talking high level concept here, and the numbers above aren't exact, but we aren't trying to write a paper here, just get a DIY fume extractor.

Anyways... the Fan:

You need to pay attention to two things when selecting a fan.

Volume, i.e. CFM
Inches of water column (in.w.g) often referred to as static pressure.

The higher velocity the air travels through a tight space, the higher the pressure.

For the sake of DIY, I'd recommend you ask for a fan that does the following.

6" Arm: Ask for a 800 CFM fan that can handle 3"-4" of static pressure.
8" Arm: Ask for a 1,200 CFM fan that can handle 3.5"-4.5" of static pressure.

A 1.5 HP 120v single phase fan should be able to do the job for either.

That should be able to handle both the arm, and the exhaust if you have anything snakey or goofy going on with an exhaust flex hose as well. Bends in duct or hose = pressure.

One little note on shielding gases... I hear this all the time. It's not an issue if you follow the advice above. It becomes a problem when you volume is so low that you need to be right on top of the weld but your velocity is high enough to capture the gases. Sticking between 800-1,200 CFM makes it a non-issue. However, people don't believe me half the time so I designed my fume arms to have an internal damper so I don't have to spend time convincing people it is not a problem. If you are concerned about it, add a damper to you setup.

Hope that helps a little. Good luck. Nothing too complex for a mechanically inclined person to figure out.

-Richard
Last edited by richardddt; 01-31-2019 at 12:06 PM.

2. WeldingWeb Apprentice
Join Date
Feb 2019
Posts
18

## Re: Fume Extractor for Under \$20

Originally Posted by IronHide
Hi all,
a few people in the "welding in the garage" thread seemed interested in my home made fume extractor.

I made a short video about it. As you can see, it is very simple, and took me about a half an hour to build and install. Final cost was \$19.46+tax. It works well.

Brilliant! I was going to do something using an old A/C squirrel cage fan which I didn't have yet. This is that but much easier. I'm going to attached mine to an old retractable cord reel so I can raise and lower it easily.

3. Jax
Join Date
Mar 2015
Posts
208

## Re: Fume Extractor for Under \$20

I'll offer a few tips that might help stir you in the right direction for gathering material to build on a shoestring budget. Make friends with someone in the hvac trade to pick up used fans as well as some other handy parts that are normally thrown away. Squirrel cage(radial) fans push & pull through ducts much better than propeller(axial) style. For the cfm range that has been talked about here,radial fans from better quality range hoods and bath vents are near perfect size/cfm. Induced draft fans from gas furnaces are also in this class. For whole building capability,120 volt blowers from gas furnaces range from aprox 100 cfm per 10kbtu on non-induced draft up to 130 cfm per 10k btu on induced draft models. Air handlers (usually 240 volt) for heat pumps require aprox 400 cfm per ton. To derate cfm,tack metal flashing inside wheel to partly cover fins rather than dampering (choking off) flow in the ducts. The latter increases's load on motor amd overheating. Your hvac source can also furnish flex duct minus insulation,dstrubition duct takeoffs for connecting duct to blower and exhust point. If you need to have fan modulate for on off cycles of welder,ask the hvac homie to wire up time delay relay,contactor and transformer from a discarded air handler.
*****Warning***** If you have propane,natural gas or fossil fuel anywhere in the building,get help from someone who understand's "backdrafting" before using a store bought or home brew extractor.
Last edited by Jax; 03-03-2019 at 01:40 AM.

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