How to measure air flow

Hi Everyone,

I was wondering what exact method you guys use to determine CFM on wall mount Indoor units? I assume its somewhat different from a ducted unit. Would you simply use manufacture air flow specs for the unit you are working on.


Thanks in advance.

Yup. :)

If you need to check on units on a regular basis I would take a velocity reading on a new unit and record it. Compare the reading at later visits to indicate potential faults.

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Originally Posted by Brian_UK

Yup. :)

If you need to check on units on a regular basis I would take a velocity reading on a new unit and record it. Compare the reading at later visits to indicate potential faults.

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Thank you!

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Originally Posted by Husky250

Hi Everyone,

I was wondering what exact method you guys use to determine CFM on wall mount Indoor units? I assume its somewhat different from a ducted unit. Would you simply use manufacture air flow specs for the unit you are working on. Thanks in advance.

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Use a good anemometer & the formula: supply face velocity in FPM *X's area in sq.ft. = CFM

If the supply outlet measurements are given, or you can measure it, divide the sq.ins., by 144 to get sq.ft., then multiple by the average cross-section airflow velocity in feet per minute (FPM) to get CFM.

Compare the resulting CFM to the mfg'ers listed rating(s).

That works the same way on duct supply diffusers. That can provide a ball-park CFM, perfect precision is near impossible when measuring airflow. You're trying to see if it is too far off where airflow should be.

To find open area of a round duct; Duct diam is 7"; 7"X7"= 49 X's .7854 = 38.04845-sq.ins divided/ by 144= 0.2672541-sq.ft. area X's FPM Velocity 600-FPM = 160-CFM.

Especially in the cooling mode; Correct Airflow is extremely important to operating performance & efficiency.