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Calculation Machine

Welding Fume Extraction CFM Calculator

Capture airflow for a welding hood or arm.

Reviewed by the Calculation Machine team · How we check our maths

Your values

ⓘ Live results

Results
Extraction airflow
840 CFM
Unflanged requirement
1,120 CFM
Saving from flange
280 CFM
At half the distance
278 CFM

Working

  1. 1100 x (10 x 1² + 1.2) = 1,120 CFM

Quick answer

Capture airflow rises with the square of distance, so getting the hood close is far more effective than buying a bigger fan.

The formula

CFM = V x (10 x X² + A) for a plain hood

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Capture distance1 ft
  • Hood face area1.2 sq ft
  • Capture velocity100 FPM
  • Flanged hood?Yes

Result

  • Extraction airflow840 CFM
  • Unflanged requirement1,120 CFM
  • Saving from flange280 CFM
  • At half the distance278 CFM

How to use the Welding Fume Extraction CFM Calculator

  1. 1Measure how far the hood face sits from the arc or fume source.
  2. 2Enter the hood face area and required capture velocity — 100 FPM suits welding.
  3. 3Add a flange to the hood; it cuts required airflow by about 25%.

Frequently asked questions

Why does distance matter so much?

Required airflow grows with the square of distance, so doubling the gap roughly quadruples the fan you need.

Is general ventilation enough?

No — local exhaust at source is the only reliable control for welding fume.

About this calculator