2) Have a simple sketch of your system
Frequently Asked Questions - Ductulator
April 4, 2022
How to calculate duct work sizes for welding fume extraction layouts and fan CFM requirements
1) Use the back of the Ductulator
3) Start with the first fume arm in line (3”). Then work your way to the last arm. Start with 3” duct work since you have a 3” arm.
4) 3” dia is equivalent to 7 sq in (see Ductulator red circled area)
5) Next arm is 3”, which is also 7 sq in
6) When you add 7 (first 3” arm) + 7 (second 3” arm) = 14 sq in. Find 14 sq in on the chart. It is equivalent to 4” diameter duct work. So when you add the second 3” fume arm your duct work needs to increase to 4” diameter.
7) Next is a 6” fume arm. This is equivalent to 28 sq in
8) 28 sq in + 14 sq in = 42 sq in
9) 42 sq in is 7.5" diameter duct work. We would round up to 8"
Note: You can use odd duct diameters at 3", 5", 7", and maybe 9". Typical to stay to even afterwards, unless customer wants odd.
10) At the fan inlet the duct work is 8”
11) The arm cfm is:
a. 3” – 170 cfm (1.5 wg)
b. 6” – 600 cfm (1.5 wg)
c. Total = 170+170+600 = 940 cfm
The fan would need to be more than 940 cfm
If you don’t have a Ductulator and would like one, email Josh Cannon (Sales@iap-airproducts.com). He can help with all your welding fume extraction needs!
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