My house is "x" square feet, how big a stove do I need to install?

Factors to consider are whether you are using the stove/fireplace as your primary source of heat, and if you want an all night burn or not.  Having too large of a stove usually is not even an issue.  With a larger stove, you can simply build a smaller fire to reduce the amount of heat produced.  However, if you have too small of a stove or fireplace, you may not be able to produce enough heat for the living space.