We heat with wood, and I can state with certainty that the 21" fan moves more air than the 2 x 12" fan to move air out of the sunroom into the rest of the house. That is even without the advantage of a shroud for the stand fan. The 2 x 12" is a window fan that the sash sets against, making a shroud. The stand fan sits a couple of feet behind the same size window on the opposite side of the room. There is a door exactly between for intake air.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching
