Wanna go down the rabbit-hole on different types of blower fan blades and when to use them?
I did.
I saw I had one fan with forward and one with backward - and here’s the skinny…
http://www.rs-online.com/designspark/fan-types-why-choose-a-forward-curved-centrifugal-fan
https://www.rs-online.com/designspark/fan-types-why-choose-a-backward-curved-centrufugal-fan
TLDR - Forward Curved for ducts with small openings, and higher back pressure