This will probably start a controversy.
I've got about the same situation. I've got two vents between levels, with dual fans, which can blow or suck through the vents.
Originally, I was trying to blow the heat from the lower stove room, up to the living room. It didn't seem to work the best. One day, while dust mopping in the area of the first floor vents, a dust bunny floated upward, but just kind of hovered, not too far, above the vent.
I decided, even though I had a return to the basement floor on the other end of the house, the cold air was right at the first floor vents and would have preferred to go down them. So, I reversed the fans to blow the cold air to the basement and put a Vernado fan at the top of the stairs, on the first floor, to send the warm air, coming up the stairs, to the rest of the house. While it isn't what i had hoped for, it's the best I've come up with so far. It does, "try" to keep the temperature down in the stove room.
Bottom line: It easiest to move cold air (I think), and let it displace the warm air to where you want it.