How do you size home HVAC?
For a quick estimate use BTU or W per area ratios by insulation and climate; for more precision, a heat-load calculation with U-values, areas and ventilation. Capacity then picks the equipment and sizes ducts or line sets.
Oversizing isn't better: equipment short-cycles, uses more energy and dehumidifies poorly.
Mini split, ducted or heat pump?
Mini splits are the cheapest per room; ducted systems distribute air discreetly through the house; heat pumps provide heating and cooling efficiently. The choice depends on existing ductwork and budget.
In cold climates check the heat pump's balance point and backup needs.
How do you cut HVAC energy use?
Improve insulation and air sealing, choose high SEER2/HSPF2 equipment, set reasonable thermostats and keep filters clean.
The SEER savings calculator estimates what you recover by replacing an old unit.