# CFM Equation Chart



## BayPointArchitect (Dec 20, 2016)

While reviewing tenant finish plans for a barbershop, I noticed that the mechanical contractor provided the following calculations.  The CFM per room seems rather small and I am wondering if these are the calculations for "fresh air" and the amount of conditioned air would be closer to 1 cfm per square foot or 5 cfm per calculated occupant load.  Not that I really need to know but I am just curious if anyone else can tell me what these formulas relate to.

*CFM Equation Chart:*

8 x 10 Break Room
8 x 10 x 8 = 640 / 60 = 10.67 = 11 cfm

5 x 10 Hallway
5 x 10 x 10 = 500 / 60 = 8.33 = 9 cfm

6 x 7 Utility/Laundry
6 x 7 x 8 = 336 / 60 = 5.6 = 6 cfm

7 x 7 Restroom
7 x 7 x 8 = 392 / 60 = 6.53 = 7 cfm

45 x 20 Main Barbershop Area
45 x 20 x 10 = 9,000 / 60 = 150 cfm

Again I say that these amounts of air flow are really insignificant unless it relates to a minimum amount of fresh air.  If you can reference the code section where this equation comes from, that would be great.
Thanks again everyone!

ICC Certified Plan Reviewer
NFPA Certified Fire Plan Examiner


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## JBI (Dec 20, 2016)

Have you asked the MC where the calculations come from?
Ventilation and exhaust chapter in the IMC are pretty much square footage, so not sure why he converted to cubic footage. Also not sure where he got the '60' value from. (Looked in both the 2015 IMC and the 2010 NYSMC - which is based on the 2006 IMC).


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## steveray (Dec 20, 2016)

Seems like he was doing 1 air change per hour...(60 minutes)


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## tmurray (Dec 21, 2016)

It doesn't look like the proper ventilation rates from ASHRAE 62.

I would agree that the MC looks like they are trying to do an ACH calculation. I don't know why they're using 1 ACH, usually this is at 0.3 for most building types.


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## BayPointArchitect (Dec 24, 2016)

I can live with this being an unsolved mystery.

Thank you everyone!


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## cda (Dec 24, 2016)

This formula worked backwards ??::


http://m.contractingbusiness.com/service/use-air-changes-calculation-determine-room-cfm


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## Paul Sweet (Dec 26, 2016)

1 air change per hour used to be a rule of thumb for infiltration, before energy codes started tightening up in the 80s.  I typically use 1/2 air change per hour.

ASHRAE 62 regulates ventilation air.  You should use the greater of the ventilation or infiltration to calculate heat loads.

cda's link appears to be for total airflow, which should be based on heat gain or loss, and not air changes per hour.

The rates in the original post might have worked back in the 80s, when ventilation was typically 5 CFM per occupant, but are way too low for present codes.


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## BayPointArchitect (Dec 27, 2016)

My heating inspector finally nailed this mechanical contractor down to determine that the mechanical contractor had no idea what he was doing.
So my heating inspector did him a favor and provided a better set of calculations.

Never-the-less, thank you everyone.


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