FTA: “In the end, I’m not really sure we can just put dissimilar fans in series. If you put a fan that can pump (say) 200 cubic feet per minute (CFM) in series with a fan that can only pump 100 CFM, what is the resulting output? Probably not 300 CFM.”

“Dissimilar” isn’t needed there.

https://www.rotron.com/Resources/Application-Notes/Series-an...:

“When applying more than one fan in a system:

- "n" fans in series will increase pressure "n" times at a given flow rate, with no additional free delivery flow. Fans in series can be useful in high resistance systems.

- "n" fans in parallel will increase flow "n" times at a given pressure level, with no additional shutoff pressure generated. Fans in parallel can be useful in low resistance systems.”