Vent Size and fan calculations making since

[ncga]

I would like a bit of help from the HVAC guys on this site.

I tend to over engineer every project and have realized some things do not make since. I am wanting to control high temps and will be moving to air cooled lights. BUT I have 6 inch fans rated at 530cfm. I also have six inch ducting. While doing some research I find six inch ducting is only good for 85 cfm.

My question is how does this work , and what is the real max?

Working out an existing set up. Can you run1 6 inch 530 cfm fans through 2 600 watt Mondo hoods with 1 300 cfm 6 inch fan on the last light and 16 feet of flex insulated ducting connecting them from a 6 x 24 filtered intake

Another project question to answer. I will pull out my kestrel wind meter to see if i can measure it.

nc

 

[sedate]

Working out an existing set up. Can you run1 6 inch 530 cfm fans through 2 600 watt Mondo hoods with 1 300 cfm 6 inch fan on the last light and 16 feet of flex insulated ducting connecting them from a 6 x 24 filtered intake

Yes. 6" Ducting can run a hell of a lot more than 85cfm. That's weird.

I dunno where you read that but it's definately bs.

6 inch duct work works fine for anything but huge commerical grows or exceptionally long runs of duct - like >25 feet or so.

The fan is the key here.

You need a real cannon fan - not a duct fan. What fan do you have? Link to the product page.

 

[ncga]

Thanks sedate It is their 6 inch fan

http://www.tjernlund.com/retail/fans.htm good pricing on Ebay


Also after looking at HVAC sites the following seamed to be the rule

On a short run a 10" flex duct will carry about 400 cfm.

These are guesstimates to close to what they are at short runs.

4" Duct 40 cfm
5" duct 60 cfm
6" duct 100 cfm
7" duct 150 cfm
8" duct 200 cfm
9" duct 300 cfm
10" duct 400 cfm
12" duct 600 cfm
14" duct 900 cfm
16" duct 1,400 cfm
18" duct 1,800 cfm
20" duct 2,300 cfm.

The 8" will only deliver 260 cfm's at the same static pressure.
You cant go by just the diameter of the pipe, a 10" will carry 4 times as much as a 5".
You need the sq. in. size, radius squared times Pi.
For 10" thats 5 x 5 x 3.14 = 78.5 square inches
For 8" thats 4 x 4 x 3.14 = 50.24 square inches
400 cfm / 78.5 sq. in. = 5.09 cfm per sq. in.
5.09 x 50.24 = 255.7 cfm for the 8" pipe.


Thanks nc