Ducting Effects on Fan CFM

Hey rollitup,

quick question.. Ive been doing some ressearch and cant find anywhere that gives a good explanation on the effect of ducting on fan cfm rating..?

for example. i have a 2x2x5 tent and im running a 6" activeair inline exhuast which is rated at 306 cfm. However, iv incorporated about 5 feet of ducting with multiple bends? would i be safe using a carbon filter that is rated at say 190 cfm or so?

with no filter my temps are at about 73


i wanna hang the filter inside tent and run the ducting out roughly 5 feet and attach my blower.

any thoughts?

bump bump
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they say a 90 degree kink reduces CFM by up to 60%...

try and work out how many degrees of total bend you have in
your ducting.

All depends on the type of the fan first of all!
A vortex (in-line) fan have much more power than most other fans and i don't think 5 foot of ducting would affect a 400cfm fan at all.

Xan2 said:

All depends on the type of the fan first of all!
A vortex (in-line) fan have much more power than most other fans and i don't think 5 foot of ducting would affect a 400cfm fan at all.

Click to expand...

Depends on the kinks in the ductwork. Not the fan. a 400 cfm fan is a 400 cfm fan.

A vortex 400cfm is not producing any more "power" than a 400cfm Can Fan. They
are both equally effected.

Shrubs First said:

Depends on the kinks in the ductwork. Not the fan. a 400 cfm fan is a 400 cfm fan.

A vortex 400cfm is not producing any more "power" than a 400cfm Can Fan. They
are both equally effected.

Click to expand...

Sorry but i think you missunderstood.

An IN-LINE(Vortex, canfan...) 400cfm fan is certainly more powerfull than any other 400cfm fan. Even a U in a 5ft duct is not going to reduce the flow, 5ft is just not enough ducting to rush a 400cfm in-line fan.

The filter should be the same cfm or larger than your fan. Using a filter rated for less cfm will reduce the fans cfm to that of the filter. In other words, your 300cfm fan will now only be able to move the 190 cfm the filter is allowing to pass through.

I use a Can-75 filter with 6" HO Can-Fan. According to their website my combination achieves 378 cfm even though the fan is rated at 440 cfm.

Don't worry about your bends, the filter size is more important, just try to keep them gradual and you'll be fine.

Xan2 said:

Even a U in a 5ft duct is not going to reduce the flow, 5ft is just not enough ducting to rush a 400cfm in-line fan.

Click to expand...

This goes against statements made by the manufacturers. So you must have spoken
to them recently and they have retracted their experimental statements, I'm assuming.

Here's an example restriction curve chart. They vary by fan but this'll give you an idea on how restrictions affect CFM.

http://www.airboosterfans.com/cf6-curve-chart.html