To offset that, the furnaces in most homes are larger than necessary. Initial cost is only one of the drawbacks of that strategy. A furnace that is too large will cycle on and off more frequently. That puts more wear on its components, wastes energy, and might cause the temperature to vary to uncomfortable levels. Also, a larger replacement furnace might require larger ducts. Without the right size ducts, airflow can be noisy.
To be sure of correct sizing and a proper installation, choose a licensed, reputable contractor who will take the time to calculate your heating needs. Such calculations take into account the climate and the size, design and construction of your house.