# Thread: Air Flow Changes per hour

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May 2008
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## Air Flow Changes per hour

i'm trying to get the formula to calculate how many times the air flow changes in a room an hour ? The air handler's Capacity is 7,000 cfm, 15 hp running 100% outside air to 5 rooms the average size of each room is 21'L X 17'W X 10' H... and if i should use the 250 to 500 scale to measure the cfm to get to the conclusion?
THANK YOU!!!
DMC357

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Dec 2007
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Connecticut
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Hi DMC357,
The formula is (( CFM * 60 ) \ room cuft. )
To get ACPH for each room, you will have to measure the cfm at each room. Good luck.

3. 21*17*10 = 3570 CF per room

3570 CF * 5 = 17850 CF

7000 CFM * 60 Min/Hr = 420000 CFH

420000 CFH / 17850 CF = 23.5 ACH

Damn. That's one air change every 2.55 minutes.

4. Or, 17,850 CF/7,000 CFM =2.55 minutes.
60 minutes divided by 2.55 minutes =23.529 ACH.

Either way, thats a lot of air, and energy to condition it.

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