How to Calculate Air Changes per Hour

There is a simple way to calculate the air changes required for any room. The calculation works two ways;

1) If you know the Cubic Volume of the room you can calculate the ACH (Air Changes per Hour)

2) If you know the CFM that has been specified for the room, you can determine how many air changes for the room.

Air changes are used by various codes to dictate a minimum amount of air that must be exchanged from a particular type of room. Hospital rooms require various air changes based on usage.

Bathrooms require a minimum amount of air changes, so knowing how to calculate the air changes required for a room is important. The amount of air changes will determine how much CFM is required to accomplish the calculated amount.

#airchanges #ach #cfm

[thegladiator]

I was so lost in this topic taking my classes for the Commercial Drying Specialist, I asked 100 times to my instructor and I couldn't understand, so I decided to look here and I came here : NOW I GOT IT !!!
Your calm and clear way to talk gets into my brain, THANKS A TON !!!

[mondoalvarez]

Great teaching!! Keep it up... no extras no blah blah blah.. thanks !!!

[RMalai]

Loud and Hear. We all heard it!! Good instructor. This is how I also teach.

[stephaniebaldwin]

Thank you sooo much for this. I've been searching online to understand this formula. Because I am a visual learner I have not understood it until I saw you demonstrate it. 😊😊

[yuanjacobderiquito]

Thank you for very informative article, it's help me a lot in my work as a hospital maintenance technician!more power to your channel!

[andyoohhh]

I was trying to figure out how to determine the number of air changes you need for a specific room. Is it based all on code? Maybe Square footage? Where can you find that information?

[neelpunghera]

As per one of your video "how to calculate CFM" in which you show a formula "total sensible btuh / 1.08(EAT-LAT)" As per this calculation CFM is not matching with this equation. And now I am confusion which one right to consider.

[kirubakaran]

How to determine ACH for a windcatcher
Which velocity we should take inlet or outlet

[AlyElhennawy]

That's great but I have a question, that 108 CFM that you got from your results, is the CFM that supplied for the room or that to be exahuasted outside the room as an return?

[neelakantarao]

Hello Sir, you explained back calculations only. First you declared 4 Air changes per hour and calculated CFM. Again same CFM value used for Air changes per hour calculations. Can you explain, how to calculate CFM without knowing the Air Changes per hour value?

[chandnee]

Thanks, very well explained and calculated

[ricardocastillo]

Does this calculation mean that based on this example, a fan rated for 108 CFM would have to run continuously for 24 hours in order to fulfill the 4 air changes per hour?

[solomongoderdzishvili]

Sorry what is different between minimum outdoir air change and minimum total air change

[vidyarthikootam]

Superb guide and explanation, thank you

[erryw]

Hi, i'm asking if the room has circulation fan just like AHU (supply fan & return fan with the same air flow) is this formula still works..?

[thermocoolofficials]

Please inform..is ACH.means change with outside air? Or just resirculate throught AHU?

[hvacrefrigeration]

Ok, I tried something about an air change per hour by, for example: if the room is using 8 hours per day, so I used 8 x volume of a room and divided by 60 and the answer is total CFM... correct?

[youflexmtq]

Hey Please Do you have any idea??
The air outlet area of the indoor unit of the air conditioner is 0.1 square meters, the flow rate is 2m/s,
the density is 1.2 kg/m3, and the flow direction is upward 45 degrees. How much is the air exchange
rate in cubic meters per hour? How many kilograms?

[a_balanced_perspective]

How many times per hour is the change of ventilation in bathrooms, toilets and kitchens?

[narendrakumarsoni]

Hello sir,
I have a 36×12×20 ft volume of a room but i dont know how much air changes per hour of that room
So pleasw tell me how to calculate cfm of my room