My previous room (previous house) was 400 square feet (for rats and snakes) and in the basement and 2 oil filled heaters were necessary to keep it in the 78 degrees range.

Now the snake room (and snake only) is 210 square feet and above the garage and I am pretty convince that 1 oil filled heater will be enough (this will be our first winter here so we will see)

Bottom line it depends on the room size and room location if the room is in the basement it will will require a little more help to maintain than a room closer to the roof.

In my opinion given the size of your room 1 will probably be enough.