We have a gas DV fireplace insert in our living room. It gets pretty warm near the fireplace. We keep the thermostat about 10 feet from the fireplace and it automatically turns it on and off to maintain the temp setting.

I think that for a room your size, you need to take into account the fact that these DV devices throw off a lot of heat, but do not distribute it very effectively. So the farther away you are from the unit, the cooler it would be. You might want to make sure the unit you select comes with a blower. If you can, check out the blower, because some of them are pretty noisy. We never use ours for that reason, but we don't need it.

I'm tempted to say you should consider 2 small units instead of one big one, so you'll get better heat distribution. But that might be overkill. A lot depends on the shape of the room, the location of the stairwell relative to the stove, etc. If the room is pretty square, a centrally located unit will probably work, provided it's not too close to the stairwell, which might draw the heat up and out the room. But if the room is long and narrow, 2 units would probably be optimal.

I hope these comments are helpful. Good luck