2 fans at different CFM?

chico1st · Post by **chico1st** » Fri Jul 02, 2010 8:59 pm

If I had one fan pushin 20 CFM and another pushing say 30 CFM and they were baffled in line with eachother (so no other air could get through) how many CFM would be pushed?
Would the fan pressure be increased?

Post by **NeilBlanchard** » Sat Jul 03, 2010 5:55 pm

This is generally just going to be noisier than either of the fans on it's own and the CFM will probably be about what the slower fan is shifting. It might help if the air flow is really constricted -- but the better solution would be to reduce the restriction and use one fan.

datapappan · Post by **datapappan** » Wed Jul 07, 2010 12:13 am

They would be pushing less than 20 cfm, albeit at higher pressure than when just using one fan.

Are you familiar with fan curves and air path impedance? Here's some in-depth:
- cfm-rating is normally at free-flow, i.e. in open-air setup (no impedance)
- putting a fan in a case, increases impedance, and so lowers cfm
- putting fans in series means adding their pressure capacity,
and forcing them both to have the same cfm

That's a quick run-though. Better answers can be given if you hint us as to what they are to be used for, please post.

/d