posted 1 month ago
This is a simple formula, originally from an old solar greenhouse book by Bill Yanda:
cfm = 16.6 Av sqrt((Tu-Tl)h)
Tu is the temperature at the top (outlet).
TI is the temperature at the bottom (inlet)
h is the height between, in feet
Av is the smallest cross sectional area of the vent, in square feet.
16.6 is a constant
It could also be written as: CFM = 16.6A sqrt(HdT)
with A as Area,
H as the Height,
dT as deltaT (the temperature difference, top(outlet) minus bottom(inlet))
It is a bit different from some other formulas, but simple and seem to work well enough.