Choosing the correct AC unit size is crucial for energy efficiency and adequate cooling. An undersized unit will run constantly, struggling to cool your home, while an oversized unit will cycle on and off frequently, wasting energy and shortening its lifespan. Factors that determine AC size include the square footage of your home, insulation levels, climate zone, window size and efficiency, number of occupants, and heat-generating appliances. Don't guess! Consult an HVAC technician to perform a Manual J load calculation to determine the precise cooling capacity your home needs.