Commercial Hood's cfm

[317069]

Three commerical kitchen equipments A, B, and C are under a hood, all of them have the same dimensions, say: 3'x 24"
so our hood would be 10'x36"x24".
equipment A needs 300 cfm/ft
equipment B needs 200 cfm/ft
equipment C needs 100 cfm/ft

1) what the total hood exhaust would be?
is it 10'x300 = 3000 cfm
or, (3*300)+(3*200)+(3*100)= 1800 cfm
or, 10'x36"x75= 3000 cfm
2) if we use cfm/ft, then what the difference is between two sizes of the same equipment, forexample: 3'x24", and 3'x36"

 

[tys90]

The IMC 2009 requires that you exhaust to the heaviest duty appliance under a hood. So for this case you need 300 cfm/ft for the entire hood. Check your local codes though.

 

[317069]

1- what if we put each equipment A.B, and C under its own small hood (4'x36"x24") then we connected all of them to a main exhaust duct with one upblast fan for all of them, does it still need 3000 cfm
2- does 10'x36"x24" need the same cfm as 10'x48"x24"?

 

[ChasBean1]

Hmmm, why not just add them? I'd go with 600 cfm.

 

[317069]

ASHRAE 90.1 says:
where a single hood is installed over multiple appliances with different duty ratings, the MAXIMUM ALLAWBLE FLOW RATE for the hood or hood sectio shall not exceed the table values for the highest appliance duty rating under the hood or hood section"

it said maximum but didn't say minimum

 

[chicopee]

If you expect concurrent useage,yes, you'll need 3000cfm

 

[ChasBean1]

Woops, misread the givens... per ft and not ft^2.

 

[Wareagl487]

When I am making a quick estimate on CFM's required, I use 300 cfm/ft to get a ballpark number. 98% of the time I send the kitchen lay-out of equipment under the hood to trusted kitchen hood reps for recommendations. Keep in mind there are a number of "low flow" hoods available on the market (Spring Air Systems comes to mind)that can significantly reduce cfm requirements.

If you want to design the hood yourself, Greenheck offers software that can help with that.

Andy W.