stacking in-line fans

.....and a good day to you all!


i need someone adept in physics:


imagine, if you will, using two 265cfm in-line fans to do your business.
running them on separate lines, a total of 530cfm are being exhausted out of the room, right?

what happens if you stack those fans, one into another, exhausting out of only one line? i know one of them is going to pull 265cfm, but will the other just be spinning it's bearings or is it going to kick out a greater amount of air??


i realize that trial and error is going to answer my question, but not until tomorrow.
i want to give someone the opportunity to shine tonight!

There is a lot to consider. Given an area of duct work of a run of length x with zero resistance, the 2 fans inline will be useless. In this case they will not add up. This is because the air flow is already moving at the same speed of the fan.(I say this with a grain of salt, because I'm really rusty on this stuff and there is a lot of people on here much more in the know and they have discussed. I know al_b_fuct has this covered a bit on his faqs as have some other people)

Where the fans inline do help is where there is a loss of flow due to resistance. (turns, tees, wyes, vertical changes up) This is where you would want the second fan to restore loss of flow. There is a link on here somewhere that references online duct flow calculators that you can input info and it will tell you max air flow. You would use this help pick your fans.

You can add the ratings together when they are ducted separately though to move air out or into a space. I hope this gets you started, and hope also someone more knowledgeable comes along to help give more data here that I am missing.