Why the box figure misleads when sizing a wood or pellet stove
Rated heating area is derived from laboratory output under controlled conditions, applied to an assumed building. Your house has a specific envelope, a specific layout, a specific elevation and a specific number of doors between the stove and the rooms you want warm. None of that is in the rating. The rating is not dishonest; it is answering a different question from the one you are asking, and treating it as an answer to yours is where oversizing starts.
What sets the demand
The envelope first, insulation, air sealing, windows, so the calculator asks about it and asks you to be honest, not optimistic. Then the area you want heated, which is commonly smaller than the whole floor plan, because heat does not travel through closed doors and up stairwells the way people hope. Then whether this is the primary heat, a zone supplement, or outage backup, which changes where in the band to look without changing the arithmetic.
The cost of oversizing, which is not money
An oversized appliance makes the room uncomfortable at its efficient operating range, so it gets damped down. Damped-down burning is cooler. Cooler flue gases deposit creosote faster: sometimes dramatically faster. The owner then experiences more frequent sweeping, blackened glass, poor heat output and a stove they blame the manufacturer for. Every part of that chain traces back to a sizing decision made from a box.
Where the band becomes a purchase
It does not, and that is intentional. The band tells you which conversation to have and which appliances are plausibly in range. What tells you whether a specific appliance suits a specific house is its own listing, the flue it will vent into, the clearances available and the hearth protection required. Those are the things that make an installation legal and safe, and none of them are a square-footage figure.